Oxygen Sensor
- When the odometer shows 60,000 or 120,000 miles, the oxygen sensor light on the instrument panel will flash. If not, there is a malfunction and system should be tested.
- Remove ECM from behind dashboard, leaving coupler attached. Warm engine to normal operating temperature. Run engine at idle speed. Using a voltmeter, connect probes to terminal No. 10 (oxygen sensor) and terminal No. 21 (ground). See Fig 1 .
- Accelerate the engine from idle to 1500-2000 RPM. Voltmeter should read between .0-.8 volts depending on engine speed. Voltmeter indicator should deflect between .0-.8 volts. If voltmeter gives proper reading, then oxygen sensor is sending correct input to ECM unit. If reading is not correct, see following list of possible causes:
Voltmeter Remains at Zero:
- O2 Sensor Wire Loose
- Intake System Leaky
- Mixture Too Lean
- Carburetor Malfunction
- Voltmeter Resistance Too Low Oxygen Sensor Defective
Remains at .8 Volts:
- Choke On, Engine Cold
- Thermal Switch Defective
- MCS Disconnected
- MCS Valve Defective
- To check feedback to oxygen sensor from the ECM, turn oxygen sensor light switch off. See Figure . Using an ohmmeter, connect positive probe to body ground and negative probe to terminal No. 17 of ECM unit. Ohmmeter indicator should deflect. If not, reverse polarity of ohmmeter probes. Turn oxygen sensor light switch on. Sensor light should flash. If not, wiring harness, light bulb or oxygen sensor switch may be defective.