Do a hard reset of the check-engine light by disconnecting the battery, turning on the car lights and pressing the horn. Wait a few minutes, and reconnect the battery. This causes the check-engine light to go out temporarily, but if the condition persists, the light illuminates again.
- Disconnect the battery
A vehicle's computer requires power to store the codes. Disconnect the battery so it no longer receives power from this source. Use a wrench to loosen the ground cable from the battery, and remove it from the post. The ground is marked with a negative sign.
- Turn on the lights, and press the horn
Turning on the lights and pressing the horn drains any residual power stored in the vehicle's computer, ensuring the computer deletes the codes and extinguishes the lamp when the battery is reconnected.
- Wait a few minutes
Leave the battery disconnected for a few minutes so the electronics in the computer can discharge.
- Reconnect the battery
Place the cable back on the post, and tighten the connection. Start the vehicle. The check-engine light goes out after starting; however, if the underlying condition is not fixed, the sensors continue to send the data to the diagnostic center. Eventually, the onboard computer senses a problem and illuminates the light again.