How to perform a GM throttle body relearn procedure

How to do a GM throttle body relearn procedure

If you’ve replaced your GM electronic throttle body or you’ve disconnected the battery, you must do a GM throttle body relearn to establish a new baseline idle. Many car makers including GM started installing fly by wire electronic throttle bodies. In those vehicles, the “gas” pedal isn’t connected to the throttle body by a cable. The pedal simply provides an electronic signal, telling the throttle body how much acceleration you’re requesting. A motor and gear reduction set inside the throttle body opens and closes the throttle plate to accomplish your request.

Over time, carbon buildup can accumulate around the throttle plate, changing it’s “home” position. If the buildup occurs gradually, the PCM “learns” the new home position. But when your battery goes dead or you disconnect it to work on your vehicle, the PCM “forgets” the adapative home position. If you replace the throttle body, the PCM won’t know and will continue to use the adaptive settings as if the carbon buildup is still in place. If you don’t do a relearn procedure, the PCM will “hunt” for a new baseline idle. It will eventually learn it on its own, but it may take over a week of driving, during which time you will experience high and low idle speeds and possibly rough idle.

Here’s the throttle body relearn procedure

1) Start the engine and let it idle in park for 3 minutes. During that period the idle may be higher idle than normal.
2) After 3 minutes, turn the engine off and leave it off for 60- seconds.
3) Start the engine again and let it idle in park for 3 minutes one more time. During these run periods you may see a check engine light. Scan for codes and if you get throttle body related codes, clear them.
4) If the idle speed is still off, drive the vehicle at speeds above 44-mph and operate several acceleration and deceleration cycles. Then repeat step #3 one last time.

The idle should now be normal

©, 2015 Rick Muscoplat

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