Engine Rough, Miss, and Oxygen Sensor DTC's

****TSB Update 77-65-12, April 1997****

Subject:
Engine Rough, Miss, and Oxygen Sensor DTCs (Replace Oxygen Sensor Jumper Harness).

Condition
Some owners may comment about an engine miss and/or roughness and a SES light.

Cause
Some oxygen sensors on the passenger side of the vehicle have been found to be damaged due to water intrusion. Approximately 20% of the oxygen sensors returned for analysis on these models have exhibited this condition. If any oxygen sensor related DTC is stored, moisture may have entered the jumper harness that connects the three passenger side oxygen sensors to the main engine harness and damage the sensor and the harness. Oxygen sensors that have been damaged by water will have corrosion on one or more of the sensors (4) terminals. The jumper harness connector at the same location should show similar corrosion. If there is undetected moisture in the jumper harness, a replacement oxygen sensor can be damaged resulting in a repeat failure. In addition, a replacement oxygen sensor may be misdiagnosed as faulty when the actual fault is undetected moisture in the jumper harness.

Correction
1. Follow the Strategy Based Diagnostics and published procedures for the specific symptom and DTC.

2. Inspect the oxygen sensor connectors for signs of moisture or "bluish-green" corrosion on the contacts and in the connector cavities.

3. If water intrusion is suspected, but no corrosion is evident, the presence of water in the sensor may be checked using a DVOM. It is very important that the sensor be at room temperature when this test is run. If the sensor is warm or if power has been applied to the sensor's heater within the previous 10 minutes, incorrect results will be obtained. Set the meter to measure resistance in the megohm range and connect it across the sensor's purple and tan contacts. A defective sensor will show a value less than 20 megohms, and the value may change continuously while the DVOM is connected to it. A good sensor will show resistance values much higher than 20 megohms and/or may indicate "OPEN."

4. If these signs are detected, replace the oxygen sensor jumper harness and all affected oxygen sensor(s). DO NOT attempt to repair the jumper harness by cleaning or replacement of corroded terminals. DO NOT use or apply any type of sealant anywhere in the oxygen sensor connectors or wires. Repair attempts to oxygen sensor harnesses generally result in a repeat failure.

5. Record all DTCs encountered during problem diagnosis on the repair order. This is needed for engineering analysis of the components.

6. Verify the symptom and/or DTC is corrected before returning the vehicle to the owner.

Important:
The new jumper harness must be routed according to the Wiring Diagram.