Applicable for most cars. Some newer (1996+) vehicles have to be electronically reset.

The most reliable method is:

  1. With engine/coolant up to normal operating temperatures.
  2. Disconnect positive battery terminal.
  3. Attempt to start the vehicle.
  4. Depress brake pedal (with battery disconnected) 10 times.
  5. Allow to sit for no fewer than 60 seconds.
  6. Reconnect battery.
  7. Start vehicle and idle until fully up to operating temperature.
  8. Shut off, reset the ECU once again.
  9. Restart, allow vehicle to idle for 1-3 minutes.
  10. Drive normally for 10 minutes
    • most vehicle do not apply any new fuel corrections above about 3/4 engine load and 3/4 max-rpm, therefore normal driving is best driving

The above method will start off your fuel trims on the right foot. But within 30-60 minutes or so of driving there usually won’t be much of a difference doing either the above or next method.

The absolute minimum method to reset learning is:

  1. Disconnect positive battery terminal.
  2. Attempt to start the vehicle.
  3. Depress brake pedal (with battery disconnected) 10 times.
  4. Allow to sit for at least 30 seconds.
  5. Reconnect battery .
  6. Start vehicle and drive away.

For newer vehicles (1996+ OBD-2), ECUs usually store fuel trims and ignition adjustments in what’s called NV memory, or non-volatile memory. This type of memory does not reset when power is lost, like many older vehicles will. This means you may need to use a specialized tool, usually in the form of a handheld OBD-2 scanner, to reset your ECU’s learned values.