An O2 sensor is a galvanic battery that provides the ECM with a voltage signal (0-1 volt) inversely proportional to the amount of oxygen in the exhaust. In other words, if the oxygen content is low, the voltage output is high; if the oxygen content is high the output voltage is low. The ECM uses this information to adjust injector pulse-width to achieve the 14.7to1 air/fuel ratio necessary for proper engine operation and to control emissions.
The O2 sensor must have a source of oxygen from outside of the exhaust stream for comparison. Current O2 sensors receive their fresh oxygen (outside air) supply through the O2 sensor case housing.
Four wires (circuits) are used on each O2 sensor: a 12volt feed circuit for the sensor heating element; a ground circuit for the heater element; a low-noise sensor return circuit to the ECM, and an input circuit from the sensor back to the ECM to detect sensor operation.
Removal & Installation
- Raise and safely support the vehicle.
Disconnect the wire connector from oxygen sensor.
WARNINGWhen disconnecting sensor electrical connector, do not pull directly on wire going into sensor.
- Remove the sensor with an oxygen sensor removal and installation tool.
- Clean threads in exhaust pipe using appropriate tap.
- Install the oxygen sensor and tighten to 22 ft. lbs. (30 Nm).
- Connect the electrical connector.
- Lower the vehicle.
- Start the engine and allow it to idle for at least 60 seconds. Using a diagnostic scan tool, check for the presence of any Diagnostic Trouble Codes (DTCs). Record and address these codes as necessary.
- Turn the ignition off, allow the sensor to cool down to room temperature disconnect the oxygen sensor wiring harness. Measure the resistance across the sensor heater control terminal and ground terminal. If resistance is not between 2 and 30 ohms, replace the sensor.
- Refer to any Technical Service Bulletins (TSBs) that may apply.
- Review the scan tool Freeze Frame information. If possible, try to duplicate the conditions under which the DTC set.
- With the engine running at normal operating temperature, monitor the scan tool parameters related to the DTC while wiggling the wire harness. Look for parameter values to change and/or a DTC to set. Turn the ignition off.
Visually inspect the related wire harness. Disconnect all the related harness connectors. Look for any chafed, pierced, pinched, partially broken wires and broken, bent, pushed out, or corroded terminals.
Perform a voltage drop test on the related circuits between the suspected inoperative component and the PCM.
CAUTIONDo not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool no. 8815 to perform diagnosis.
- Inspect and clean all PCM, engine, and chassis grounds that are related to the most current DTC.
- If numerous trouble codes were set, use a wire schematic and look for any common ground or supply circuits.
- For any Relay DTCs, actuate the Relay with the scan tool and wiggle the related wire harness to try to interrupt the actuation.
- For intermittent Evaporative Emission trouble codes perform a visual and physical inspection of the related parts including hoses and the Fuel Filler cap.
- Use the scan tool to perform a System Test if one applies to failing component. A co-pilot, data recorder, and/or lab scope should be used to help diagnose intermittent conditions.