How to check engine light codes?

Learn a method to read and clean your trouble codes

Early Warning System

Modern vehicles are equipped with onboard computers that monitor the critical systems in your car and warn you when something is going wrong. Your check engine light is your vehicle computer’s way of telling you that there may be a problem and your car requires service as soon as possible.
So many possibilities

The reasons for a check engine light activation range from something as simple as a loose gas cap to something as serious as a faulty catalytic convertor. Below is a list of a few of the possible problems that could cause your check engine light to activate.

 - Loose gas cap
 - Problem with the MAF sensor or circuit
 - System running too lean or too rich
 - Cylinder misfire
                                                 - Knock sensor circuit malfunction
                                                 - Insufficient EGR (Exhaust Gas Recirculation) flow
                                                - Catalyst system efficiency below threshold
                                                - Faulty oxygen sensor

These are just a few of the hundreds of causes and symptoms that would result in an engaged check engine light. Decoding your dashboard is a science.
How to read trouble codes?

The only way to know why your Check Engine Light is on is to plug a scan tool into your vehicle's OBD II diagnostic connector. The scan tool will then display the trouble code or codes that have been set. Most scan tools will display the trouble code and a one line description or definition of the code. Some basic code readers may only give you the number but no definition.

Note: You cannot diagnose a Check Engine Light without a scan tool! (Although you can access trouble codes on some vehicles via the Driver Information Display if you know the procedure for doing so).

If you don't have a scan tool, many auto parts stores and even some repair shop will do a FREE plug in diagnosis to read out the codes. Most repair shops and dealerships, however, usually charge a flat diagnostic fee of 75€ to 100€ or more to perform a scan tool diagnostic check to read out trouble codes.
If you have trouble code..

Write down the code number. Don’t erase the codes until you have written this information down because you will need it later to diagnose the problem.
The code will tell you which sensors or systems are experiencing a problem. If the scan tool does not provide a definition, you will have to look up the code definition where ever you can find it (online, in a shop manual…)
How to clear trouble codes?

The best way to erase trouble codes is to use a scan tool. The tool communicates with the vehicle computer and tells it to erase the codes. It does not alter any other learned settings that should be retained for normal vehicle operation.

The worst way to clear codes is to disconnect the battery. In older vehicles (those made before 1996), disconnecting the battery even for a few seconds, or removing the power fuse for the engine computer (PCM) will erase the codes, along with all of the other learned settings the computer has stored over time.

Note: Clearing the codes will not keep the Check Engine light off. Sooner or later, the codes will reset and the Check Engine light will be back on unless the problem that caused the code to set in the first place has been diagnosed and repaired.

Caution: Disconnecting the battery to clear codes on many 2006 and newer vehicles is NOT a good idea because it may cause the PCM to forget critical settings. This may have an adverse effect on the operation of the transmission, climate control system and other functions. This, in turn, may require special "relearn" procedures using a factory scan tool or professional grade scan tool to restore proper operation of the affected systems.

Note: Clearing codes with a scan tool, or disconnecting the battery will also reset all of the OBD system monitors back to zero, meaning your vehicle won't be accepted for an OBD plug-in emissions inspection until all of the monitors have run and completed.

How reset your warning light ?


Before pay a mechanic, destroy carbon thanks to decarbonization.

Preventive engine cleaning enables you to restore engine parts rather than replacing them, thereby saving vehicle owners on costly parts, such as a new turbocharger (1.350€ - 3.100€), catalytic converter (600€ - 2.000€), DPF (600€ - 2.000€) or EGR valve (370€ - 500€).

These problems result mainly from poor combustion, which stifles the engine.

So before replacing your engine parts, try Carbon Cleaning. A dirty engine as the result of carbon deposits is the new threat to vehicle performance.

Make your online diagnosis
Center Locator
Find the Carbon Cleaning center closest to you
With the Carbon Cleaning solution,
you can help extend the life of your car engine
without the need to replace so many expensive parts.
Locate a center
near you :
Become a distributor-partner of Carbon Cleaning
As a member of the Carbon Cleaning network,
you are an independent vendor. To help you grow
your business, we put all of our experience and expertise
at your disposal.
Contact us with any questions
or for more information about how to become a partner.
Professional Information and Contact
Already have a Carbon Cleaning Pro account? Sign in!
Discover our new machines !!!
Replace the coolant in less than 5...
Thanks to our Flash Cooling stations, the draining, bleeding and replacement of the coolant is carried out in less than 5 minutes. Increase your turnover and save time with these...
Discover our new machines !!!