Oxygen Sensor: Testing and Inspection
OXYGEN SENSOR HEATING ELEMENT CHECKINGFastener Locations For Air Filter Housing:
To gain access to the oxygen sensor connectors, the engine compartment cross brace, intake air ducts and air cleaner box must be removed. The locations of the fasteners for the air box are identified by the arrows in the diagrams. The connectors are located behind the left cylinder head.
Oxygen Sensor Connectors Location:
1. Locate oxygen sensor heating element connector and disconnect from harness (this is the two terminal connector coming off the wire leads to the sensor).
2. Start engine and idle.
3. With engine running, check voltage between terminals on harness side of connector.
^ Should be battery voltage.
If not, check for one of the conditions listed below
a. Fuse #5 burned.
b. Open or grounded circuit between fuse #5 and oxygen sensor heating element connector terminal #1.
c. Open ground circuit between heating element connector terminal #2 and ground connection on engine block.
d. Faulty fuel pump relay or open circuit between fuel pump relay terminal 59/87 and fuse #5.
Repair as necessary and begin again.
4. If battery power is present, connect ammeter between harness connector and sensor connector (use appropriate connectors to complete the circuit), set to 10 amp range.
^ With engine running, current to the heating element should be between 0.5 amps (hot sensor) and 3.0 amps (cold sensor). If current is greater than 3.0 amps, or less than 0.5 amps, replace sensor.
OXYGEN SENSOR CHECKING
1. Disconnect oxygen sensor signal wire harness connector (single pin connector leading from the oxygen sensor).
2. Connect DVM between harness side of connector and engine ground (set to millivolt scale).
3. Turn ignition ON and note voltage.
^ Voltage should be approx. 450mV (0.45 volts).
If not, check for:
a. Open or grounded circuit between ECM terminal 28 and sensor harness connector.
b. Sensor wire pinched, worn through, or burned (signal wire shorted to wire shielding).
If no wiring problems are found, and there is still no voltage from ECM terminal 28 to oxygen sensor, or if the voltage is greater than 0.6 volt, then the ECM is faulty.
4. Connect dwellmeter (or duty cycle meter) in parallel with white wire to #1 cyl. fuel injector. (Use appropriate parallel test lead and jumper wire to complete the circuit to the injector).
5. Reconnect oxygen sensor, start engine and run at 2,000 rpm for 1 minute, then let idle.
6. With engine idling, note dwell (or duty cycle).
^ Dwell should be varying slightly. (The exact value is not important for this test. We are only interested in the change in dwell in the next step.)
7. Impose a lean condition by creating a small vacuum leak (unplug a manifold vacuum hose) and observe dwell.
^ Dwell should increase slightly and continue to vary as ECM responds to the imposed lean condition.
If not, replace oxygen sensor.