Chart 8 Front Heated Oxygen Sensor Diagnosis

Chart 8:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The PCM provides a .45 volt reference signal to the oxygen sensor on CKT 412. When warm, a properly operating oxygen sensor will drive the .45 volt reference lower (below .45 volt) to indicate a lean mixture, and higher (above .45 volt) to indicate a rich mixture. The oxygen sensor signal voltage will toggle from rich to lean rapidly, at least one toggle every two seconds, if the PCM is in good control of the air/fuel mixture.

Powertrain Chart 8 is designed to be used after the oxygen sensor circuit and PCM operation have been verified through the Powertrain System Check and PCM code diagnosis. Chart 8 should identify oxygen sensors that are:

A. Open - not able to drive the .45 volt reference signal high (rich) or low (lean)

OR

B. Shorted - Sensor output is fixed high (above .45 volt) or low (below .45 volt) due to contaminants or internal sensor faults.

NOTES ON FAULT TREE:

1. With the engine running warm (coolant temperature 85 degrees C or greater) and at fast idle, observe engine data parameter PD32. Voltage should swing below .3 and above .6 volt.

2. While running the engine at a fast idle, observe the "Open/Closed Loop" status light, the "AUTO" annunciator on the CCDIC. If the PCM switches the system to "Closed Loop" operation, then the oxygen sensor is OK. If the PCM remains in "Open Loop" operation and the coolant temperature PD04 is above 85 degrees C, then replace the oxygen sensor.

3. If the voltage remains between .30 and .60 for a minimum of 1 minute, replace the oxygen sensor and check for cause of oxygen sensor contamination.

4. If there is no voltage variation, there is intermittent terminal contact or the oxygen sensor is faulty.