Rick's Free Auto Repair Advice

Turn off the check engine light

How to check trouble codes and turn off the check engine light

So you had a check engine light and decided to guess and replace parts without actually reading the trouble code and now you want to know how to turn off the check engine light. Well, dude, if the light is still on, there’s still a trouble code stored in the computer. Rather than throw more parts at the problem, it’s time to invest in a scan tooluse a scan tool to check trouble codes and clear them

Pro grade scan tool for DIY. Lists trouble codes and live data. Clears trouble codesor even a code reader.

Jeepers, invest in a scan tool!

I still don’t understand why home mechanics don’t invest in an inexpensive code reader (at the very least). They’re cheap. And if you’re trying to save money by working on your own car, you should at least have the proper tools. It’ll pay for itself on the first repair….but I digress.

But if you don’t own a scan tool or code reader and just want to clear trouble codes and turn off check engine light, here’s how to do it without a scan tool.

Disconnect the battery cables

Disconnecting the battery cables will often clear the trouble codes and turn off the check engine light.

But it’s a bit more complicated than that. All PCMs and ECMs have adapative memory strategies built in. That adaptive memory allows the PCM/ECM to deviate from factory programming to account for changes in your engine as it ages. So disconnecting the battery to turn off the check engine light isn’t enough. You must also clear the adaptive memory, also call keep alive memory or KAM.

Short the battery terminals

Then touch them together for 30-seconds. That drains all the power out of the PCM/ECM capacitors that can sometimes hold KAM in the chips. When you reconnect the terminals, you’ll be starting from scratch.

Clean the battery posts and terminals

clean battery posts and battery cable terminals

This kind of corrosion causes starting and charging problems. Clean it off!

Now is the perfect time to clean the battery posts and battery cable terminals. Use a battery terminal cleaning brush or sandpaper. Then

clean battery posts and terminals with a battery cleaning brush

Clean battery posts and terminals with a special wire brush

reattach the terminals and tighten. You can spray the entire connection with a battery terminal protective spray to reduce corrosion.

How to relearn adapative memory

Now that you’ve cleared the KAM memory, you vehicle won’t run right. That’s because it’s running off of factory programming that was designed for a brand new vehicle.

But your computer has to relearn the condition of your engine and transmission. The procedure is a bit different for every car maker, but generally it takes about 10 starts from fully cold to fully warm for the computer to relearn your particular engine/transmission.

You can speed up the learning process by varying your driving pattern to include stop and go and highway driving. Keep in mind it’s not just 10 starts—the computer needs to see a cold engine (a cold engine is an engine that hasn’t run for at least three hours) at startup and then see it warmed up so the temp gauge is in the middle range. It also needs to see you drive it, most often for about 20-mins. So you can’t do the relearn by sitting in your driveway and cycling the on/off 10-times. During the relearn, expect the engine to act strangely as the PCM/ECM relearns.

Check engine light still on? Read this post.

©, Rick Muscoplat


Posted on by Rick Muscoplat

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