Oxygen Sensor Heating 1 Ahead of Catalytic Converter - Below Lower Limit

P1115

Oxygen Sensor Heating 1 Ahead of Catalytic Converter - Below Lower Limit

Function
The heated oxygen sensor (HO2S) generates a current signal starting at approx. 300 °C that determines the fuel/air mixture. This signal is used for the regulation of fuel injection. The oxygen sensor is heated to bring it quickly to operating temperature to start oxygen sensing earlier.

Diagnosis conditions
During a cold start (H02S readiness after 20 seconds) the time t1 is measured. t1 is the time from switching the H02S heating on until one H02S is operational. Then a time t2 is calculated (t2 =2.5*t1). t3 is the time from switching the H02S heating on until the other H02S is operational. If t3 is greater than t2, a fault is recognized.
When a fault is recognized, the resistance comparison of the H02S heating is blocked. If no fault is recorded, the calculated resistance of the H02S heating is compared to a threshold only after 400 sec. If the resistance is too high, a fault is recognized for both H02S heating circuits.

P1115-P1119:

NOTE:
- Heating of oxygen sensors (1 and 2) ahead of the catalytic converters is supplied by an output stage. Under certain conditions, both heating circuits can be recorded as a fault even though only one is faulty.
- If an H02S signal fault is recorded in addition, correct this fault first and then road test vehicle or perform short test.
- If all 4 heating circuits are stored in the fault memory, check the common B+ supply.

Oxygen sensor 1 - cylinders 1 to 3
Oxygen sensor 2 - cylinders 4 to 6

Connector color gray - after catalytic converter
Connector color black - ahead of catalytic converter Wiring Diagram

Wiring Diagram







Diagnosis Procedure







1 Check resistance of H02S heating.

1. Remove connector of HO2S 1/2 ahead of catalytic converter.
2. Connect ohmmeter on pin side to pins 1 and 2.
Display: 1.8 - 2.5 ohms at 20 °C.

3. Connect ohmmeter on pin side to pin 1 and HO2S housing.
Display: Infinity ohm

2 Check wiring from DME control module to disconnection point of HO2S 1/2 for continuity, short to B+ and short to ground.

1. Remove connector of HO2S 1 and 2 ahead of catalytic converter.
2. Connect special tool 9616 to wiring harness (DME control module connector).
3. Connect ohmmeter to special tool 9616, pin 30, and disconnection point of HO2S 1/2 ahead of catalytic converter, pin 2.
Display: [<] 1 ohm

4. Connect ohmmeter at sleeve to connector, pin 2, and ground.
Display: Infinity ohm

5. Remove ignition, injection and oxygen sensor heating relay and bridge terminals 30 and 87.
6. Connect voltmeter at sleeve to connector, pin 2, and ground.
Display: 0 V

3 Check output stage of DME control module.

1. Remove connectors to oxygen sensors.
2. Start engine and run at high speed for 3 minutes.
3. Connect voltmeter at sleeve to pin 1 (positive) and pin 2.
Display: battery voltage