Jeep Wagoneer/Commando/Cherokee 1984-1998

Oxygen Sensor



This component of the system provides a variable voltage (millivolts) for the Micro Computer Unit (MCU) that is proportional to the oxygen content in the exhaust gas. In addition to the oxygen sensor, the following data senders are used to supply the MCU with engine operation data.


  1. Start the engine and bring it to normal operating temperature, then run the engine above 1200 rpm for two minutes.
  3. Backprobe with a high impedance averaging voltmeter (set to the DC voltage scale) between the oxygen sensor (02S) and battery ground.
  5. Verify that the 02S voltage fluctuates rapidly between 0.40-0.60 volts.
  7. If the 02S voltage is stabilized at the middle of the specified range (approximately 0.45-0.55 volts) or if the 02S voltage fluctuates very slowly between the specified range (02S signal crosses 0.5 volts less than 5 times in ten seconds), the 02S may be faulty.
  9. If the 02S voltage stabilizes at either end of the specified range, the ECM is probably not able to compensate for a mechanical problem such as a vacuum leak or a high float level. These types of mechanical problems will cause the 02S to sense a constant lean or constant rich mixture. The mechanical problem will first have to be repaired and then the 02S test repeated.
  11. Pull a vacuum hose located after the throttle plate. Voltage should drop to approximately 0.12 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a lean mixture condition. Reattach the vacuum hose.
  13. Richen the mixture using a propane enrichment tool. Voltage should rise to approximately 0.90 volts (while still fluctuating rapidly). This tests the ability of the 02S to detect a rich mixture condition.
  15. If the 02S voltage is above or below the specified range, the 02S and/or the O2S wiring may be faulty. Check the wiring for any breaks, repair as necessary and repeat the test.

Removal & Installation

The sensor uses a permanently attached pigtail and connector. This pigtail should not be removed from the sensor. Damage or removal of the pigtail or connector could affect the proper operation of the sensor. Keep the electrical connector and louvered end of the sensor clean and free of grease. NEVER use cleaning solvents of any type on the sensor!

The oxygen sensor may be difficult to remove when the temperature of the engine is below 120°F (49°C). Excessive force may damage the threads in the exhaust manifold or exhaust pipe.

  1. Unplug the electrical connector and any attaching hardware.
  3. Remove the sensor using an appropriate sized wrench or special socket.

To install:
  1. Coat the threads of the sensor with an anti-seize compound before installation. New sensors are usually precoated with this compound.

DO NOT use a conventional anti-seize paste. The use of a regular paste may electrically insulate the sensor, rendering it useless. The threads MUST be coated with the proper electrically conductive anti-seize compound.

  1. Install the sensor and tighten to 30 ft. lbs. (40 Nm). Use care in making sure the silicone boot is in the correct position to avoid melting it during operation.
  3. Engage the electrical connector and attaching hardware if used.