P043

Circuit Description

The PCM provides a 0.45 volt reference signal to the oxygen sensor on CKT 412. When the oxygen sensor is cold (below 200°C), the oxygen sensor signal voltage will be around 0.45 volt and the PCM will keep the system in 'Open Loop' operation. When the oxygen sensor is warm (above 200°C), the oxygen sensor will swing from rich to lean rapidly, at least one swing every two seconds, if the PCM is in good control of the air fuel mixture. Code P043 is designed so that if the oxygen sensor stays at a rich voltage for more than 50 seconds during the test conditions, Code P043 will set. Code P043 will set when:

1. There is an oxygen sensor circuit fault giving a false rich indication.
OR
2. When the air fuel ratio is actually rich due to a fuel control or emission system fault.

Test Condition(s)

1. Codes P014, P015, P016, P021, P022, P026, P027, P031, P032, and P034 not set.
2. Throttle position switch open.
3. TP sensor between 5~40 and 250.
4. Coolant temperature between 81.5°C and 131°C.
5. Oxygen sensor ready.
6. Engine speed 800 rpm or greater.
7. Low coolant level and engine overheat not present.
8. Traction control not active.
9. MAP value greater than 20.2 kPa.
10. Evaporative Emission (EVAP) canister purge on full with TP sensor greater than 100.
11. Long term fuel trim not in effect.

Failure Condition(s)

Oxygen sensor remains rich (534 mV (0.534 V) or greater) for more than 50 seconds.

Action Taken

1. PCM turns 'ON' the 'SERVICE ENGINE SOON' MIL
2. PCM enables Evaporative Emission (EVAP) control solenoid if Code P045 is also set.
3. Transaxle shift adapts are maintained at current levels.

Notes on Fault Tree

1. If Code P017 is also set, diagnose it first because an Oxygen Sensor not ready can cause other emission related problems.
2. If the Oxygen Sensor is operating correctly, voltage will fluctuate below 0.6 volt. A rich sensor/condition will cause the voltage to remain above 0.6 volt.
3. If less than 0.95 volt is measured, the PCM and CKT 412 are OK.