Engine Light Check
"CHECK ENGINE" light is used by ECM to indicate and diagnose a fault in electronic control system. Power is supplied to the light from ECM fuse and ground is supplied through the ECM. Light is normally "ON" with key "ON," and should turn "OFF" when engine RPM exceeds 400 RPM.
- This step checks for power to ECM. Normal reading is battery voltage.
- This step checks for an open circuit to ECM. Normal reading at ECM terminal "E" should be battery voltage.
- This step checks for good ECM ground. If there is a poor connection to ground, voltage at terminal "K" will be more than 1 volt. The poorer the ground, the higher the voltage.