Applicable for most cars. Some newer (1996+) vehicles have to be electronically reset.
The most reliable method is:
- With engine/coolant up to normal operating temperatures.
- Disconnect positive battery terminal.
- Attempt to start the vehicle.
- Depress brake pedal (with battery disconnected) 10 times.
- Allow to sit for no fewer than 60 seconds.
- Reconnect battery.
- Start vehicle and idle until fully up to operating temperature.
- Shut off, reset the ECU once again.
- Restart, allow vehicle to idle for 1-3 minutes.
- 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:
- Disconnect positive battery terminal.
- Attempt to start the vehicle.
- Depress brake pedal (with battery disconnected) 10 times.
- Allow to sit for at least 30 seconds.
- Reconnect battery .
- 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.