Ford Full-Size Vans 1989-1996 Repair Guide

Oxygen Sensor



See Figure 1

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Fig. Fig. 1: A common oxygen sensor

An Oxygen Sensor (O 2 S) or heated Oxygen Sensor (HO 2 S) is used on all engines. The sensor is mounted in the right side exhaust manifold on some V8 engines, while other V8 engines use a sensor in both right and left manifolds. The sensor protrudes into the exhaust stream and monitors the oxygen content of the exhaust hoses. The difference between the oxygen content of the exhaust gases and that of the outside air generates a voltage signal to the PCM. The PCM monitors this voltage and, depending upon the value of the signal received, issues a command to adjust for a rich or a lean condition.


No attempt should ever be made to measure the voltage output of the sensor. The current drain of any conventional voltmeter would be such that it would permanently damage the sensor. No jumpers, test leads or any other electrical connections should ever be made to the sensor. Use these tools ONLY on the PCM side of the wiring harness connector AFTER disconnecting it from the sensor.


See Figures 2, 3 and 4

The oxygen sensor must be replaced every 30,000 miles (48,000 km). The sensor may be difficult to remove when the engine temperature is below 120°F (48°C). Excessive removal force may damage the threads in the exhaust manifold or pipe; follow the removal procedure carefully.

  1. Locate the oxygen sensor. It protrudes from the exhaust manifold or pipe and looks somewhat like a spark plug.
  3. Detach the electrical connector from the oxygen sensor.
  5. Spray a commercial solvent onto the sensor threads and allow it to soak in for at least five minutes.
  7. Carefully unscrew and remove the sensor.

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Fig. Fig. 2: Unplug the oxygen sensor electrical connector

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Fig. Fig. 3: Use a wrench to loosen the oxygen sensor and remove it from the exhaust pipe

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Fig. Fig. 4: Do not allow contaminants such as grease, oil or anti-seize compound to contact the sensor prior to installation

To install:
  1. Coat the new sensor's threads with anti-seize compound made for oxygen sensors. This is NOT a conventional anti-seize paste. The use of a regular compound may electrically insulate the sensor, rendering it inoperative. You must coat the threads with an electrically conductive anti-seize compound.
  3. The proper installation torque is 30 ft. lbs. (42 Nm). Do NOT overtighten.
  5. Reconnect the electrical connector. Be careful not to damage the connector.