Feedback System
- Start engine, and warm it to operating temperature. Ensure idle speed and timing are adjusted to specification. Increase engine speed to about 2000 RPM for 2 minutes under no-load condition. Using a small screwdriver, turn diagnostic mode selector screw on ECM.
- With mode selector screw turned fully clockwise for at least 2 seconds, inspection lights will begin to flash. Turn screw fully counterclockwise. This switches ECM to Mode II, which is used to monitor exhaust gas sensor feedback signals.
- With engine speed at 2000 RPM for 2 minutes, LED should flash at least 5 times during a 10-second period. If sensor does not respond as indicated and no other faults which may affect air/fuel mixture are indicated by ECM self-diagnostic system, use a voltmeter to verify input signals to ECM are correct. If input signals are correct, replace oxygen sensor. If input signals are not correct, replace ECM.