How To Erase Pending Codes? 97 Most Correct Answers

A Permanent Diagnostic Trouble Code (DTC) is stored when a DTC is confirmed and the Malfunction Indicator Lamp (MIL) illuminates. A permanent trouble code can only be cleared by the module strategy and cannot be cleared by clearing trouble codes with a scan tool, resetting a keep-alive memory (KAM), or disconnecting the battery. Permanent error codes are displayed in the integrated diagnostic system (IDS) from version R104. The intended use of the permanent DTC is to prevent vehicles from passing an in-use inspection by simply disconnecting the battery or clearing DTCs with a scan tool before the inspection.

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If your vehicle is due for an emissions test, you may be wondering if a check engine light will affect the result of the test. There are several factors that can affect the result of your emissions test, and many people are unaware of the main causes of a test failure.

So can you pass emissions when the check engine light is on? The short answer is no. Ignoring this light will cause you to fail your emissions test, and many states don’t even conduct an emissions test if your check engine light is on in your vehicle.

What is the purpose of the emissions test?

An emissions test can be performed in 5 minutes or less and involves a technician scanning your vehicle identification number and then connecting a cable to your vehicle’s on-board diagnostics or OBD II.

It is a more accurate measurement of emissions and costs much less than ‘tailpipe’ tests previously used. An emissions test can typically be completed in less than 5 minutes.

All vehicles manufactured since 1996 are equipped with this onboard diagnostic system which is in place to identify any emission problems your vehicle may have and alert you before it becomes a bigger problem.

The OBD alerts you to a problem so you can repair your vehicle and prevent unhealthy air and excessive pollutants from entering the air, helping you avoid shorter engine life and wasted fuel that could result in an expensive mechanic bill.

Can you pass emissions when the check engine light is on?

If your vehicle is 1996 or newer, it likely has OBD2 capabilities. Then the check engine light has a direct impact on whether it passes the emissions test, and often your car is not even tested if the light is on at all.

Older vehicles might stand a chance, but that’s only because expectation isn’t as important for older cars as it is for newer models.

A check engine light can be an indicator of several problems with your vehicle, which is why you cannot pass your emissions test if it is illuminated. It could reveal a simple problem or even be a sign of something much more serious, which is why you won’t pass the test.

How can I pass the emissions test?

To pass an OBD-II emissions test, your vehicle must have a few things:

Your vehicle must have a working “Check Engine Light” and an OBD port.

The Check Engine Light must not light up.

Your vehicle must successfully complete the OBD II system monitors.

Why is my check engine light on?

For many people, the check engine light can be an irritating and repetitive problem caused by their vehicle’s computer, but this only happens when one or more diagnostic trouble codes are stored in your car’s computer and the light stays on as long as that is present.

It may illuminate when there is a problem that could or is affecting your car’s emissions control system, which is why your car will fail an emissions test when this light is on.

If the light stays on consistently with no performance issues, it means there is a permanent fault that cannot be resolved without fixing it and you should find the source of the problem before it causes problems with your engine management system, performance and emissions come under control.

When this happens, it means that a vital component of your engine has a serious fault and is no longer safe to drive. The most common causes for a check engine light to come on are:

Bad oxygen sensor.

Loose fuel cap.

Spark plugs need to be replaced or will fail.

The catalytic converter is defective.

Problems with the airflow sensor.

Check engine light is on – now what?

So if your check engine light is on and you have an emissions test that you need to pass, you have a few options for solving the problem.

You should ensure that your check engine light is not alerting you to a problem that needs your attention as it could cause irreversible damage to your vehicle.

You cannot turn off the check engine light or use an OBD2 scanner to reset the light because your vehicle goes through a self-check cycle when testing emissions. Also, most automotive catalytic converter and EVAP monitors take time to run, meaning you may need to drive your vehicle for several days. This gives the OBD-II time to allow trouble codes or the check engine light to reappear.

Using an OBD-II scanner

You must use a scanner to determine the cause of your check engine light and fix the problem before you can pass your emissions test. Use a scan tool on your vehicle to pinpoint the problem and ensure you pass your emissions test. Here’s how:

Connect to the OBDLink app. Tap on “Monitors”. In the top right corner, click the menu icon to select the state you live in. The screen will then automatically display a ‘Not Ready’ warning, meaning your vehicle would fail the emissions test, or a green ‘Ready’ tick indicating it would pass.

This scanner also allows you to pre-test your vehicle to confirm if there are any issues or if it passes the emissions test before taking it to be tested.

If your vehicle is older than 1996 you may not have a port for a scan tool so you may get lucky and get away with the light coming on.

frequently asked Questions

Is the check engine light related to emissions?

The check engine light signals that the onboard diagnostic system has a problem related to the ignition, exhaust system, fuel or emissions in your car.

What can I put in my gas tank to pass emissions?

If you want your car to run better or want a little help passing an emissions test, you can pass your emissions test by adding two cans of Sea Foam Motor Treatment to a low fuel tank and then driving 20 miles.

What can cause emissions to fail?

Reasons why your vehicle may fail the emissions test include an overdue oil change, an illuminated check engine light, worn spark plugs, a loose gas cap, dirty air filters, and a rich air/fuel mixture.

Can you pass emissions with stored codes?

Your car or vehicle can pass the emissions test with a pending trouble code as long as the check engine light is not illuminated and the required emissions monitors are ready.

Conclusion

If your vehicle needs an emissions test, a check engine light is a guaranteed way to get turned away immediately, but luckily there are ways around this that can allow your vehicle to do so without breaking the law.

Fixing the problem is often the best way to remove these warning lights and if you are unsure as to why your vehicle is exhibiting persistent faults you should consult a local workshop or mechanic for a professional opinion to ensure your vehicle is safe to drive.

So can I pass emissions when the check engine light is on? The quick answer is no, because on most vehicles manufactured from 1996 onwards, your check engine light will cause you to immediately fail your emissions test and be dismissed.

By using one, you can identify the cause of your problem and find the best course of action to resolve it.

You can also check out these other VehicleFreak articles:

How long can you drive with the check engine light on?

What does check exhaust system mean? (How to repair and reset)

How long to drive after computer reset to pass emissions test?

Chances are you’ve fixed your check engine light problem BUT the light is still on! And it gets on your nerves. It may have cost you a fortune.

Then why is the light still on?

Here’s what you probably don’t know: After you wipe the car’s computer, you have to drive about 50-100 miles.

As you drive your car, the computer monitors all the sensors and registers the results.

With GOFAR you can constantly monitor your vehicle diagnostics. Get a diagnostic app.

Here are the details:

System status Explanation READY The Check Engine Light has not come on. The system works perfectly. Hooray! NOT READY Your car has not been driven long enough after resetting the codes.

Solution: Continue driving until the system displays a READY state. NOT APPLICABLE Your vehicle does not support this status monitor. Just ignore it.

But wait a minute, there are other important things to consider. So let’s take a closer look.

What causes the check engine light to come on?

First of all, there are many important components in your car and when they fail, they can cause the Check Engine Light to come on.

Surprisingly, it could be something as simple as not tightening a loose gas cap after filling up! Sounds silly? But it is not.

Sometimes it could be a faulty car part that has triggered the check engine light. Some of the common auto parts that can cause the check engine light to come on are:

Defective catalytic converter

Defective ignition coil

Bad spark plugs and cables

Defective oxygen sensor

Air mass meter defective

Faulty charging system

You can read more about each of these errors and what to do about them on the Check Engine Light page.

Warning: very often a faulty sensor can be the cause of your check engine light coming on.

And if you’re not careful, you could end up spending a lot of money on an expensive car part, only to find out later that the problem was a faulty sensor.

Sound familiar?

Of course, if your car has a problem, take it to the mechanic for repair. And that’s understandable.

But here’s the problem: how many times have you been surprised at the shop by the news that your car needs an expensive repair?

What if you could personally check your car’s problem before going to the mechanic? So that you are always one step ahead of your mechanic. To really check if the mechanic is telling the truth?

Here’s the kicker: with GOFAR, a handy diagnostic code scanner that plugs under the vehicle’s dashboard, you can read your car’s fault codes yourself.

Understanding your car’s diagnostic codes

Sensors can trigger falsely

Your car’s computer is constantly recording any troublesome diagnostic codes reported by the sensors.

Here’s a little background on how the sensors work.

The only way the computer can tell there is a problem or a device is failing is when a sensor reports the problem

Each sensor reports a specific code

If the computer has stored an error code, the check engine light will illuminate to alert you

Each error code reported to the computer is uniquely registered and linked to the sensor that reported it.

When a sensor reports a defective device, the check engine light comes on. Even if the sensor itself is defective, the light will still come on

The fact is that your car has sensors for many components. Sometimes a sensor will fail or get stuck and report a bad code. If your mechanic is honest enough, they will tell you that because replacing a bad sensor is very affordable.

Related: Auto Warning Lights Resource Center

To determine if the sensor is defective, you can conduct a small experiment. Clear the codes from your computer and see if the check engine light comes on again.

But a wiser move would be to do your own engine diagnostics with GOFAR, an affordable OBD code scanner that reports over 300 common car faults in plain English.

This way you can find out why your check engine light is on. Now let’s take a look at GOFAR in detail, ready?

GOFAR diagnostic code scanner

While you were at the mechanic’s, you may have noticed that he plugged in a code scanner under the dash to read the engine trouble codes from the car’s computer.

Don’t you think it would be great to know what trouble codes the computer is reporting regarding the check engine light before you go to the shop?

It’s totally doable!

You can get your own code diagnostic scanner. But not just any scanner – most of them report in technical jargon, which can be overwhelming if you’re not a technician.

All you want is your car’s faults explained in plain English, right? GOFAR does just that and more!

Here’s how GOFAR, your little car buddy, will make your life a lot easier:

Notifies you via the app on your phone when your car is sick. The severity of the vehicle fault is also explained.

You will deal competently with mechanics because GOFAR explains the 300 most common car problems in plain language.

You can set reminders so you never forget the important dates of your car. This way you stay protected, stay safe and avoid fines.

GOFAR Bonus: A little device that helps you save fuel!

If you have a 1996 or newer car model, GOFAR will work fine with your car. When in doubt, just run a quick compatibility test.

We bet you’re pretty excited and ready to enjoy all these great benefits. So grab your very own GOFAR now!

Why it pays to buy a GOFAR

First, what customers are saying about GOFAR.

Next, watch this video to learn the benefits you will enjoy by owning GOFAR.

Easy and convenient car maintenance

How to read your GOFAR

Step 1: Download the app

The GOFAR app is available on Google Play and the App Store. The app is the window to your car’s efficiency, performance and health.

Once you’ve downloaded the app, it guides you through the setup process with nice, clear images – it takes a few minutes.

Step 2: Connect the adapter

Plug the adapter into the vehicle’s diagnostic port on the dashboard. It’s as easy as plugging in a power cord.

Step 3: Attach Ray to the dashboard

Once you have placed the beam on the dashboard, connect it to the adapter using the thin custom cable. It’s as easy as plugging in headphones.

Voila! They are all installed!

From now on you will receive notifications on your phone when there is a problem with your car. Every 2 seconds, GOFAR monitors your car to save you fuel, taxes and maintenance.

Watch this video for a broader view of GOFAR, your car’s little buddy.

How it works

This is how you can determine if there really is an engine problem.

As you now know, a faulty sensor can cause the check engine light to come on.

Since there’s no way to know right away if the cause is a faulty sensor, you’ll need to clear the codes and then see if it comes back after a while.

If the light comes back on, there are a few more steps you need to take to determine if the problem is a faulty sensor or one of the many causes of a check engine light coming on, such as: B. a defective catalytic converter.

When clearing the codes using the Clear Codes feature, the system status changes to Not Ready.

Drive 80 to 160 km (50 to 100 miles). Carry out several single journeys until the system reads the status of all components again.

“Multiple trips” means that you turn off the engine and start a new trip each time. So it’s not just 100 miles in one ride. It’s more like doing three rides of about 30 miles each.

After that, reconnect the scanner and read the System Status to see if the Not Ready condition has been cleared.

diagnosis of the problem

After you reset the codes, one of two things will happen:

If the Not Ready status changes to Ready and the check engine light does not come back on, the problem may be an intermittently faulty sensor.

If the check engine light comes back on, the scanner will give you this faulty code again. That would indicate that you indeed have a component error as indicated by the code. In this case, at least you know you’re spending money to fix a real problem.

Note that if you turn on the ignition without starting the engine, all of the instrument panel lights will illuminate momentarily to check that they are all working.

Let’s pack up

It is now clear that your check engine light will go off if you identify and fix the cause of the fault.

Sometimes only a defective sensor needs to be replaced and the light goes out after a while. And sometimes it could be a faulty part.

Tired of the guesswork? And want to be sure what the check engine light is telling you? GOFAR offers a reliable, secure and affordable solution.

Install GOFAR in your car to get easy English trouble codes for 300+ common car problems.

You can check if your car is compliant or visit the site to learn more about understanding your car’s check engine lights.

The light can clear itself. For example, if you leave the gas cap open while filling up, the light will illuminate and a code will be entered into the computer’s memory. Once the cap is back on and a drive cycle occurs that allows the computer to see that everything is OK, the light will turn off. The light goes out, but the code remains in the computer until erased (for whatever reason, e.g. lack of power or manually erased by a handheld device).

Of course, if the problem is something that requires a mechanic’s touch, the light won’t go out. Mechanical beasts don’t heal themselves. Whenever something crosses the thresholds set in the computer, the light comes on. This can be anything from a bad heater element in an O2 sensor to a bad electrical circuit or lack of continuity in a MAP sensor. Each one throws a very different code that won’t turn off until the problem is fixed.

The only thing worse than a lighted engine is it’s off but still showing an error code!

Whatever caused the trouble code may not have happened often enough to trigger both the check engine light and a trouble code to turn on, so you should use an OBD2 scanner to properly diagnose the problem. If you are having trouble identifying the problem yourself, you should see a mechanic.

A pending engine code will trigger a trouble code but not the check engine light. Pending engine codes indicate that your car knows something is wrong, but it’s not yet a damage-causing problem.

There are a few other reasons why the trouble code might persist after the check engine light has gone off, such as:

Problem was solved by itself

The code remains in the long-term memory of your engine

Electrical issue is preventing the check engine light from illuminating

The problem is not emissions related

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Whether you’re a mechanic or just want to know what’s going on under the hood of your vehicle, a basic drive cycle is critical to understanding repairs and emissions testing. This is usually useful when performing a car diagnostic test yourself using an OBD2 scanner.

What is the driving cycle?

Without going too far into the weeds, a basic drive cycle will ultimately help you or your mechanic know how successful recent repairs have been and what – if anything – needs re-evaluation. It’s a basic cycle that helps your vehicle’s computer (Powertrain Control Module) to self-diagnose and update Check Engine Light Codes, AKA OBD2 Codes.

How do you run a driving cycle?

Running a drive cycle is easy, but takes a bit of preparation and time. It can also vary by vehicle make, make, model and year, so be sure to read your owner’s manual for additional information and specifics.

However, these are 10 general steps to complete a basic driving cycle:

1. Clear all OBD II trouble codes with your OBD2 scanner. The drive cycle cannot begin until this step is complete.

2. Make sure your fuel tank is between 30% and 70% full.

3. Check the quality of your battery and alternator. Jump starting your vehicle is not an option if you want to run a real drive cycle.

4. Let your vehicle rest for eight hours. During this time, do not put the key in the ignition or unlock the car doors.

5. Start your car, put it in park or neutral and let it idle for two or three minutes.

6. Turn on your headlights, heater, and defroster for at least two minutes.

7. Drive to where you can safely reach 40 km/h. Make a slow, full stop at each stop sign or traffic light. Slowly and steadily increase your speed to 35 mph and then to 45 mph.

8. Find a freeway entrance and accelerate normally to collide with other drivers. Stay in the slowest lane and steadily increase your speed to 55 mph or 60 mph. Engage cruise control and maintain speed for at least five miles.

9. Find an appropriately sized exit ramp and drive to the end to allow your vehicle to decelerate naturally. You can use your brake at the end of the ramp.

3. Return home or to your mechanic and repeat step number seven. Upon arrival, park your vehicle and let it idle for a minute or two.

Run an OBD-II scan

You or your mechanic can now perform an OBD II scan and determine if your vehicle is repaired and ready to pass an emissions test. It’s also used when you’ve cleared the code to identify what the problem might be and what fix will get the job done. Remember that a simple drive cycle should mimic a typical person’s commute. When this happens, your engine’s computer runs a series of tests to ensure everything is working as it should.

How long does it take to complete a drive cycle

It takes eight hours to prepare, but overall a simple drive cycle test should take around 30 minutes, with around 20 minutes of actual driving. By understanding the overall condition of your vehicle, you can ensure it runs smoothly and lasts a long time. Keep an eye on your dashboard notifications and run regular checks if possible – it will be worth your time and money in the long run.

What if a new OBD2 code shows up?

After getting back on the road and driving certain miles the check engine light will come on again when a new OBD2 code shows up. But don’t worry, we’re here to make sure you’re all prepared. Nonda’s Smart Vehicle Health Monitor can monitor your vehicle’s health and read all OBD2 codes. Pairing it with the ZUS app gives you a full diagnosis of your codes as well as a special short video to teach you how to fix them at home before completing another drive cycle. Check out the video below and see how it can help you save thousands of dollars on car expenses:

How To Fix Engine Code P0420 In 3 Minutes [3 DIY Methods / Only $4.97]

Recommendation: Start your DIY diagnostics for FREE

With an OBD2 scanner, the car diagnostic test could be done at home. Learn more about how to do a simple DIY car diagnostic test and try nonda’s Car Code Reader with a FREE device and APP!

Last modified: Tue 4 Feb 2020 at 11:47 am

Standard or “generic” codes

Standard or “generic” codes (sometimes called “P-codes”) are a set of standardized diagnostic codes that turn on the Check Engine Light and are readable on any OBDII compliant vehicle, regardless of make and model.

Standard codes generally cover the engine and emissions equipment, reporting issues such as misfires, vapor leaks, failed O2 sensors, etc.

There are three types of generic/standard OBDII codes:

Pending Codes

A pending code will not turn on your check engine light and indicates that a system in your vehicle is behaving abnormally, but not so much as to indicate an actual problem.

For example, a temperature sensor might have a normal operating range of 90-110 degrees, but 80-120 degrees is considered acceptable. Once the sensor starts reading 85 degrees, it’s outside of the “normal” range, but it’s not yet a problem, so it shows a pending code.

Confirmed Codes

A confirmed code indicates that a vehicle system has an issue that requires your attention. In the temperature sensor example above, once the reading falls below 80 or above 120 degrees, the vehicle would also issue a confirmed code.

Permanent Codes

Permanent codes are a special type that was introduced recently and cannot be erased with a scan tool. If you have a permanent code, the vehicle will clear it itself once the cause has been rectified and enough data has been collected by driving in various conditions (idle, stop and go, highway).

In general, permanent codes cover emission-related devices.

Extended or manufacturer codes

Extended codes cover all non-engine related vehicle systems including:

Section

air bags

transmission

Body Control Modules (lights, turn signals, doors, etc.)

HVAC

stereo

Transfer case/4WD/AWD

Etc

Extended codes are different for each manufacturer and are not accessible with generic scan tools, you will typically see four different types:

P-codes – powertrain related (extended engine codes, transmission etc.) C-codes – chassis systems (ABS, suspension etc.) B-codes – body codes (BCM, HVAC, SRS, Stereo etc.) U-codes – in general related to the electrics/vehicle network (e.g. modules no longer react etc.)

To check which codes are supported by your vehicle, enter your year, make and model in our FAQ!

Dan Ferrell writes about DIY car maintenance and repair. He holds certifications in Automation and Control Technology and Technical Writing.

Retrieve OBD Trouble Codes

Repairing your car becomes less of a mystery when you learn how to retrieve OBD (On-Board Diagnostic) trouble codes. These codes are stored in the computer’s memory when the Check Engine Light (CEL) or Malfunction Indicator Light (MIL) illuminates on your dashboard.

These OBD trouble codes will point you in the direction of the potential problem. For example, a trouble code may reveal an abnormal change in behavior in one or more of the engine circuits or sensors that affect the emissions control system: a failed crankshaft position (CKP) sensor, camshaft position (CMP) sensor, mass air flow (MAF) sensor, or any other sensor or its electrical circuitry.

To diagnose complex electronic problems in newer cars, today’s auto technicians require a diverse range of skills, specialized equipment, knowledge and experience. Without their training and equipment, you will have a hard time solving any auto emissions problem by simply pulling and interpreting diagnostic trouble codes.

On the other hand, you can deal with many engine systems yourself, especially if you enlist the help of your repair or service manual.

In this guide, you’ll find ways to deal with error codes that indicate simple fixes you may be facing, and suggestions for tackling more difficult tasks.

The OBD system has become more sophisticated since 1982, when the California Air Resources Board mandated the introduction of OBD in all vehicles sold in the state.

In 1996, automakers introduced a standardized OBD-II (second generation) system with more capacity and complexity to better control hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and evaporative emissions. Following in the same vein, modern vehicles are now equipped with computerized modules that use codes to identify potential faults related to anti-lock braking systems (ABS), supplemental restraint systems (SRS), body controls and many other systems.

Retrieving Trouble Codes on First Generation Systems (OBD-I).

Before the release of the second generation On-Board Diagnostic (OBD-II) system in 1996, automakers used various methods to retrieve data from the computer’s memory and had their own code designations for each individual fault.

For example, on Chrysler models, you have to turn the key on and off three times, count the number of times the Check Engine flashes, and use the number to look up diagnostic codes. To access the codes on a General Motors model, you can use a jumper wire or paperclip to jumper the designated terminals on a diagnostic connector (usually under the dash) and note the number of times the Check Engine Light flashes. Getting the trouble codes on a Ford model is pretty much the same, except you use an analog voltmeter and get the code number by counting the number of times the needle on the voltmeter bounces. The diagnostic connector is usually located in the engine compartment on these models.

Even so, with OBD-I systems you may be able to use an automatic code reader to retrieve the codes. Most auto parts stores carry basic code readers and scanners, and you can also buy them online. However, if you own a pre-1996 model of car, consult the repair manual for your particular vehicle make and model or a computer code manual before purchasing so you will know exactly how to retrieve the codes. Most auto parts stores carry these manuals as well.

Your vehicle repair manual or computer code guide will help you interpret the trouble codes. Just remember that OBD-I codes can vary from one vehicle model to the next, so be sure to look up the code for your specific vehicle make and model.

Retrieving Trouble Codes on Second Generation (OBD-II) Systems.

Today’s vehicles are equipped with complex engine control systems that require expensive equipment to access and analyze all of the data stored in a car’s computer during a failure. The good news is that the trouble codes you are most interested in on OBD-II systems have been standardized so they have the same meaning across all vehicle models from manufacturers. And you can buy relatively inexpensive aftermarket scan tools that can get you some of the diagnostic codes that you can use to troubleshoot simple engine timing system problems and perform maintenance.

A scan tool along with your repair manual can help you save hundreds of dollars a year on simple repairs. And the more you learn about your car systems and how they work, the more experience you gain to do more maintenance and other simple repairs on your own car.

On 1996 and later car models you can use a code reader or scan tool to retrieve the codes. Connect the tool to the data connection port located under the dashboard on the driver’s side. Then follow the instructions that come with your tool or in your repair manual to retrieve the codes.

Your vehicle repair manual or computer code guide will help you interpret the trouble codes.

Why your computer stores an OBD code

Your car’s computer is constantly receiving information from sensors and sending information to actuators as electrical signals. The number of systems that the computer “talks” to depends on the make and model of your vehicle.

To know if the systems are working properly, the computer compares the information it receives with the data stored in memory. If any of the signals received do not match a pre-configured value or range of values, the computer can store a trouble code and turn on the check engine light or wait for another drive cycle to confirm a potential problem. This depends on the type of error detected. But as soon as your car’s computer confirms a possible fault, it stores the specific fault codes and warns you.

You can then retrieve the code(s). As discussed above, you can get the code through the data link connector with a piece of wire, a voltmeter. by turning the ignition key; via a code reader or scan tool. It is best to follow the instructions in your vehicle repair manual for your particular make and model. If you can retrieve the codes with a code reader or scan tool, follow the instructions that came with your tool carefully.

Decode diagnostic codes

A typical diagnostic trouble code consists of one letter and four numbers. It may look something like this: P0136.

P: The letter at the beginning of the code indicates the overall function of the problematic system (powertrain, chassis, body, etc.). In this case the powertrain.

0: The next digit could be a number associated with a standard code type, such as a 0; or a number 1, referring to a specific car manufacturer code.

1: The next number indicates the function of the system that registered the problem. In our example, it tells you that the system in question is measuring the amount of fuel and air entering the engine.

36: Finally, the next 2 digits refer to the component or circuit in question and the type of problem found. When it does, it’s telling you that the downstream heated oxygen sensor in the bank 1 section has either detected an air/fuel mixture problem; or the component itself – or its circuitry – stops working.

Where can I find information about Diagnostic Trouble Codes (DTCs)

Your vehicle’s repair manual

Your scan tool manual

Online auto repair forums

The network

Where to find information about diagnostic trouble codes

Armed with the trouble code, you can find out the meaning of the code by consulting your vehicle repair manual or a computer code recovery tool manual. You can also find other code interpretation sources by searching online or posting a question on one of the many auto repair forums on the internet.

If you used a code reader or scanning tool to retrieve the code, your tool’s manual will likely have a list of the codes and what they mean. Your local auto parts store or your dealer’s service department can also help you.

Once you know the meaning of your trouble codes, you can proceed to troubleshoot the component itself and its circuitry. You can consult your vehicle repair manual for this. The manual not only explains how the various systems and components in your vehicle work, but also helps you to locate and troubleshoot many of these components and systems step by step.

You can also find help from auto technicians online at one or more auto repair forums on the internet.

One thing to keep in mind when dealing with trouble codes: Every time the computer stores a diagnostic code, it points you towards the system or potential part involved in the error, but you still need to troubleshoot that specific part or circuit to find out which component is to blame, if any. Sometimes an error code that appears to be from one system was triggered by another component in a related system.

If you find that you cannot complete a particular repair, you can still use the DTC information to help a workshop isolate a problem and provide a cost estimate for the repair. Request quotes from different stores in your area so you can make an informed decision.

With the help of a simple code reader or scan tool, there is much you can do to repair and service your own vehicle when you see the Check Engine Light come on.

vehicle repair manuals

Test your knowledge of Check Engine Lights

Choose the best answer for each question. The solution key is below.

What does a flashing check engine light mean? A normal trouble code has been stored in memory.

You have an engine problem that you shouldn’t worry about just yet.

You have a problem that can damage the catalytic converter.

They had an engine problem that the computer took care of.

Solution key

You have a problem that can damage the catalytic converter.

interpreting your score

If you have 0 correct answers: sorry, the correct answer is number 3.

If you got 1 correct answer: You are right. A flashing engine light warns of possible damage to the catalytic converter.

This article is accurate and truthful to the best of the author’s knowledge. The content is for informational or entertainment purposes only and is not a substitute for personal or professional advice on any business, financial, legal or technical matter.

Answer questions

Question: My ABS light is on and I have found instructions on how to get the codes, but it says to ground the data link connector port with a suitable wire harness. What exactly do you mean by a suitable harness? Can I use a test lamp to ground it or do I need a thicker jumper wire?

Answer: You can probably get a suitable wiring harness from your dealer. However, if you want to do it manually, you can use a paper clip. If you have the repair manual for your particular model, you can probably learn how to ground it using the clip or a suitable jumper wire.

Question: What equipment is used to retrieve information from OBD?

Answer: You can use a code reader or scan tool – relatively inexpensive ones can be found at your local auto parts store or online. Try Amazon.

Question: Can I get diagnostic codes from my 2006 car computer if the battery is completely dead?

Answer: Disconnecting the battery will erase the “keep alive memory” that stores the error codes. If the battery still had some energy and went “dead” at idle and you didn’t remove the battery, you may find a P0562 code.

The light can clear itself. For example, if you leave the gas cap open while filling up, the light will illuminate and a code will be entered into the computer’s memory. Once the cap is back on and a drive cycle occurs that allows the computer to see that everything is OK, the light will turn off. The light goes out, but the code remains in the computer until erased (for whatever reason, e.g. lack of power or manually erased by a handheld device).

Of course, if the problem is something that requires a mechanic’s touch, the light won’t go out. Mechanical beasts don’t heal themselves. Whenever something crosses the thresholds set in the computer, the light comes on. This can be anything from a bad heater element in an O2 sensor to a bad electrical circuit or lack of continuity in a MAP sensor. Each one throws a very different code that won’t turn off until the problem is fixed.

I have a 2010 Corolla with 166,000 miles on it. I’ve never had any major problems with the car. Last Saturday I drove about 300 miles and just as I was about to go home 3 lights on my dash came on: Check Engine Light, vsc and Traction Control off. All 3 light up at the same time. I didn’t notice any difference in driving the car, it changed gears, accelerated, broke down, etc. all normal. Using an OBD II scan tool I go to code p2757. P2757 is: Torque Converter Clutch Pressure Control Solenoid Control Circuit Performance or Stuck Off. I left my car overnight and today I turn on my car and the 3 lights are off. I’m making an app to take it to Toyota in a few days, but now that the lights are off can the Toyota techs still get the code that showed up when the lights were on?

I did NOT reset the battery like some people do, I just turned my car on as usual and the lights were off.

So, will the technicians be able to call up the code to diagnose the actual problem? Can it be that there is no problem with the car since the lights go out by themselves? My car is due for an emissions test soon. Will my car pass the emissions test if the light is off, or will it fail because the emissions test station finds codes in the ECM’s memory?

Thanks in advance.

The only thing worse than a lighted engine is it’s off but still showing an error code!

Whatever caused the trouble code may not have happened often enough to trigger both the check engine light and a trouble code to turn on, so you should use an OBD2 scanner to properly diagnose the problem. If you are having trouble identifying the problem yourself, you should see a mechanic.

A pending engine code will trigger a trouble code but not the check engine light. Pending engine codes indicate that your car knows something is wrong, but it’s not yet a damage-causing problem.

There are a few other reasons why the trouble code might persist after the check engine light has gone off, such as:

Problem was solved by itself

The code remains in the long-term memory of your engine

Electrical issue is preventing the check engine light from illuminating

The problem is not emissions related

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