P1117

P1117
Oxygen sensor heating 1 ahead of catalytic converter - below lower threshold.

P1121
Oxygen sensor heating 2 ahead of catalytic converter - below lower threshold.

Function
The heated oxygen (HO2) sensor generates a current signal starting at approximately 300°C that determines the fuel/air mixture. This signal is used for the regulation of the fuel injection. To assure that the HO2 Sensor reaches its operating temperature earlier, the HO2 Sensor is heated. The HO2 Sensors after the TWC are used to monitor the conversion rate.

Diagnostic conditions
During a cold start (HO2S readiness after 70 seconds) the time ti is measured. t1 is the time from switching the HO2S heating on until the time an HO2S is operational. Then a time t2 is calculated (t2=2.0*t1). t3 is the time from switching the HO2S heating on until the time the other HO2S is operational. When t3 is larger than t2, a fault is recognized. When a fault is recognized, the resistance comparison of the heating of the HO2S is blocked. If no fault is recorded, the calculated resistance of the HO2S heating is compared to a threshold after 450 seconds. If the resistance is too high, a fault is recognized for both HO2S.

NOTE:
- Heating of HO2S (1 and 2) behind the TWC is operated by an end stage. It is possible that both heating circuits are recorded as a fault although only one heating is faulty.
- If an additional HO2S fault is recorded, correct this fault first and road test vehicle. When all 4 heating circuits are stored in the fault memory, check the joint voltage supply.

HO2S 1 - cylinders 1 to 3
HO2S 2 - cylinders 4 to 6

Connector color gray - after TWC
Connector color black - ahead of TWC





Wiring Diagram.





Check resistance of HO2S heating.
1. Remove connector for HO2S 1/2 behind TWC.
2. Connect ohmmeter on pin side to pin 1 and pin 2.
- Specified value: 1.8 - 2.5 ohms at 20°C
3. Connect ohmmeter on pin side to pin 1 and the oxygen sensor housing.
- Specified value: infinite resistance.

Check wiring from ECM to HO2S, connectors 1/2 for continuity.
1. Remove connectors for HO2S 1/2 behind TWC.
2. Remove ECM connector.
3. Connect ohmmeter to ECM connector pin 1 and connector for HO2S 1/2 after TWC, pin 2.
- Specified value: < 1 ohm
4. Connect ohmmeter at sleeve to connector, pin 2, and ground.
- Specified value: infinite resistance
5. Remove ECM relay and bridge terminals 30 and 87 b.
6. Connect voltmeter at sleeve to connector, pin 2, and ground.
- Specified value: 0 Volt.

Check ECM final stage
1. Remove connectors for oxygen sensors.
2. Start engine and run engine at high speed for ten minutes.
3. Connect voltmeter at sleeve to pins 1 (plus) and 2.
- Specified value: battery voltage