Oxygen Sensors

The most likely cause of oxygen sensor faults is sensor failure induced by handling damage. Oxygen sensors require careful handling, as they have a ceramic element within the sensor which can break if mistreated.

On GEMS vehicles with the 4-wire oxygen sensor, check for the following:

^ Handling damage causing failure of the sensing element or the heater element. An oxygen sensor OBD II fault will be stored in GEMS. The sensor output/heater circuit must be checked before replacement. Inspection of the sensor core may reveal knocks or dings.

^ Sensor voltages that do not switch or appear intermittent. This can be caused by GEMS harness connector terminals widened. Repeated removal/replacement of the harness connectors onto the GEMS unit can lead to reduced tension of the terminals onto the connector pins. The recommended way of re-tensioning them is to back out the terminal in question and on the underside of the terminal press down onto the tab with a suitable blunt object (ball-point pen) sufficiently to restore the terminals grip.

^ The downstream oxygen sensor lead on bank A, may be burned if it is not properly in its retaining clip (Range Rover only).

^ The upstream oxygen sensor lead on bank B, may get displaced during off-road use and cause it to contact the exhaust downpipe (Range Rover only).

^ The clamp on the GEMS harness by the battery box may also trap the sensor wire into contact with the shielding wire before entry into the GEMS unit (Range Rover only).