How to Disconnect a Car Battery to Reset the Computer

by Arthur Heberger

Sometimes people think that if you reset the computer, or electronic control module, in your car, it will fix the problems that your engine light is warning you about. It won’t. The engine light is warning you that a sensor has sent a signal to the ECM that it is out of specification and should be checked. If you have checked and repaired the problem, it may be necessary to erase diagnostic trouble codes if the engine light stays on. The best way to do this would be with a scanner, but if you don’t have one, disconnecting the battery will do the trick on many vehicles. However, disconnecting the battery will not only erase diagnostic trouble codes but also erase drivability, security and radio codes in many vehicles. Locate any codes and have them and the drivability learning procedures on hand before disconnecting the battery.

Step 1

Clean any corrosion off of the battery and terminals with a can of spray-on battery cleaner. Disconnect the negative battery cable and then the positive cable with a combination wrench. Clean the battery posts and terminals with the post and terminal cleaning tool, so you have a good connection when you’re done. The best type of tool is the wire-brush type. With the reamer type there is a danger of taking off too much material and causing a loose connection.

Step 2

Hold the positive and negative cable ends together so they're touching each other but not the battery.

Step 3

Wait five minutes for the diagnostic information to be erased. Install the positive battery cable and then the negative cable. Program any radio or security codes following the manufacturer’s directions.

Step 4

Follow the steps for any drivability learn procedures necessary on your year and model. Many vehicles will go through these procedures automatically if you drive for 10 to 20 minutes. However, you may have a very low idle, or sometimes stalling, until the system learns, so it’s best to get the procedure if you can. For example: On a 2002 Nissan Altima, there is an accelerator-pedal-released-position learning procedure as follows: With the accelerator pedal fully released, turn the ignition switch to the “on” position and wait two seconds. Turn the ignition switch to the “off” position and wait 10 seconds. Turn the ignition switch to the “on” position and wait two seconds. Turn the ignition switch to the “off” position and wait 10 seconds. The ECM has now learned where the accelerator pedal should be when fully released. Different cars will have different procedures, but with most, just driving the car will do the trick.

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