Monitoring Procedure (Sensor)
Diagnostic Codes:- P0131/P0132
- P0133
- P1137/P0137
- P1138/P0138
- P0139/P0151
- P0153/P0152
- P1157/P0157
- P1158/P0158
- P0159
Heated Oxygen Sensor - HO2S
Monitoring Procedure
The oxygen sensors are first tested when a fuel system fault is suspected; the results of further periodic tests on the response rate of the sensors are compared to standards.
If a sensor is faulty, then the default will be to switch to using fuel feedback control on the diagnostic sensor for that bank, and if that sensor is not working correctly then the next default action will be to switch to open loop fuelling. If the test response rate is lower than the standard then the test will fail; the output will also be monitored to determine maximum and minimum signal voltages and if these are not within the limits then the test will fail. If these tests are not passed then a fault event is recorded and if the count exceeds a given limit then a fault is registered.
The strategy will report to the Diagnostic Status Manager (DSM) when all the tests have been performed once; the DSM will then decide whether to store a fault code and illuminate the MIL Lamp.
HO2S Circuit (HO2S No. 1 Only Shown):
HO2S Characteristic:
HO2S Interface Circuit And Characteristic
HO2S Circuit Low Voltage
HO2S Circuit Low Voltage - Bank 1 Sensor 1 P0131
HO2S Circuit Low Voltage - Bank 1 Sensor 2 P0137
HO2S Circuit Low Voltage - Bank 2 Sensor 1 P0151
HO2S Circuit Low Voltage - Bank 2 Sensor 2 P0157
The output voltage of the HO2S is monitored for values which are lower than the expected range. The HO2S low voltage threshold is 14.65 mV.
Possible causes of fault:
- HO2S signal wire short circuit to ground.
- HO2S fault.
- HO2S sensor tip too hot - heater error, or loss of full load enrichment.
- ECM interface circuit fault.
HO2S Circuit High Voltage
HO2S Circuit High Voltage - Bank 1 Sensor 1 P0132
HO2S Circuit High Voltage - Bank 1 Sensor 2 P0138
HO2S Circuit High Voltage - Bank 2 Sensor 1 P0152
HO2S Circuit High Voltage - Bank 2 Sensor 2 P0158
The output voltage of the sensor is monitored for values which are higher than the expected range. The H02S sensor high voltage threshold is 4.989 V
Possible causes of fault:
- HO2S disconnected
- HO2S ground or signal wire open circuit or short circuit to battery voltage
- HO2S tip too cold - heater error
- HO2S fault
- ECM - interface circuit fault
HO2S Circuit - Slow Response
HO2S Circuit - Slow Response - Bank 1 Sensor 1 P0133
HO2S Circuit - Slow Response - Bank 1 Sensor 2 P0139
HO2S Circuit - Slow Response - Bank 2 Sensor 1 P0153
HO2S Circuit - Slow Response - Bank 2 Sensor 2 P0159
Periodic tests on the response rates of the sensors will be compared against reference rates, if the response is lower than the reference, then the test will fail.
Possible causes of fault:
- H02S harness fault
- H02S contaminated
- H02S fault
Lack of HO2S Switch Indicates Lean
Lack of HO2S Switch Indicates Lean - Bank 1 Sensor 2 P1137
Lack of HO2S Switch Indicates Lean - Bank 2 Sensor 2 P1157
The sensor output is monitored to determine the system control setting; if this is not within the required limits then the test will fail.
Tests are performed on the sensors to check for sensor output signals at either the upper or lower limit values; if a signal, at a limit, is detected then fuelling changes will be introduced to move the signal off the limit. If this is successful then a fuelling fault is suspected.
Possible causes of fault:
- Exhaust air leak
- HO2S loose - not fitted correctly
- HO2S wiring fault - sensor open circuit
- HO2S heater problem - tip temperature too cold
- HO2S wires crossed
- HO2S failure - remains lean - high resistance
- ECM fault - H02S input circuit fixed - indicating lean
Lack of HO2S Switch Indicates Rich
Lack of HO2S Switch Indicates Rich - Bank 1 Sensor 2 P1138
Lack of HO2S Switch Indicates Rich - Bank 2 Sensor 2 P1158
The sensor output is monitored to determine the system control setting; if this is not within the required limits then the test will fail.
Tests are performed on the sensors to check for sensor output signals at either the upper or lower limit values; if a signal, at a limit, is detected then fuelling changes will be introduced to move the signal off the limit. If this is successful then a fuelling fault is suspected.
Possible causes of fault:
- H02S wiring fault - sensor short circuit to ground
- H02S heater problem - tip temperature too hot
- H02S wires crossed
- H02S failure - remains rich - low resistance
- ECM fault - H02S input circuit fixed - indicating rich