Rick's Free Auto Repair Advice

Turn off the check engine light yourself

How to turn off the check engine light yourself

If you have a check engine light on and have fixed the problem, here’s how to turn off the check engine light.

#1 If you have a code reader or scan tool, navigate to the code reading section and press the “clear trouble code” selection.

#2 If you don’t have a code reader or scan tool, disconnect the battery terminals and leave them unhooked for at least 15 minutes, OR touch the two battery cables together for a minute. That will wipe out the trouble codes and the adaptive memory, basically resetting the entire computer.

Be aware that after clearing the computer, it will have to relearn all of its “adaptive memory” settings. That means your car may not run the same when you first start it up. It takes about 10 cold starts for a computer to completely relearn the proper settings.

# 3 Drive the vehicle. Each time your start your car and run it through a heat-up cycle, the vehicle computer will put all the systems through self-tests. If the fix you tried works, the computer will clear the code and reset the check engine light.

What if you can’t turn off the check engine light?

#1 The trouble code stored in the computer is a permanent code. You can’t clear a permanent code. The only way to turn off the check engine light is to fix the root cause and perform a drive cycle.

See this post on the different types of trouble codes

If you automatically replaced whatever sensor was listed in the trouble code without doing any further testing, you just make the single most common DIYer mistake. Many times the sensors are telling the truth and the root cause lies elsewhere.

#2 You haven’t driven the vehicle long enough. See this post on readiness monitors. The computer puts each system through a battery of tests. If the fix you completed actually fixed the problem, and your readiness monitors have run and passed, the computer will automatically reset the check engine light.

# 3 There are more trouble codes still in memory. Inexpensive code readers and scan tools can’t read all trouble codes. There are powertrain codes (P codes), body codes (B codes), Chassis codes (C), and network codes (U codes). Plus, there are generic codes and manufacturer-specific codes.

Many times a DIYer will post on an auto forum saying their check engine light is on but there are no trouble codes stored. Computers don’t think for themselves and they don’t randomly try to mess with your head. Here’s the bottom line: if your check engine light is on, there IS at least one trouble code stored in the computer. If your code reader or the auto parts store’s code reader can’t find a code, then you’ll need a pro-level scan tool. Again, if the light is on, a code IS stored.

©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat

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