P0156

P0156
Oxygen Sensor Behind Catalytic Converter (Cylinders 4 - 6) - Short Circuit of Wires.

Function:
To diagnose the readiness for operation of the oxygen sensors, the position of the sensor voltage is evaluated (in case of certain faults or conditions, the diagnosis is disabled).

Diagnosis Conditions:
Diagnostic Trouble Code P0156 is stored in the Engine Control Module when the voltage is between - 40 mV and + 40 mV for more than 200 seconds.

Conditions for the diagnosis of the oxygen sensor signals:

- Sensor heating is active.

- Oxygen sensing behind catalytic converter is active.

- No Secondary Air Injection.

- No faults detected for fuel tank ventilation and Secondary Air Injection.

NOTE: When DTC P0156 is stored, DTC P1121 (sensor heating) is stored as well.

Wiring Diagram:




Diagnosis Procedure:



1. Check wiring harness.
1. Remove all oxygen sensor connectors.
2. Connect voltmeter at sleeve to pins 3 and 4 of oxygen sensor connector 2 behind catalytic converter.
3. Switch ignition on.

Specified Value: approx. 450 mV.

4. Connect voltmeter at sleeve to pin 3 and ground.

Specified Value: approx. 720 mV.

If the measurement according to items 3 and 4 does not show the specified values, remove ECM connector and check wires for short circuit.

If the wires are OK, replace ECM.

2. Check function of oxygen sensor.
1. Heat the oxygen sensors (road-test car under load or run engine without load at high engine speed).
2. Connect Porsche System Tester 2 or scan tool and read voltage of oxygen sensor 2 behind catalytic converter.
3. Change the fuel/air ratio with acceleration bursts.

Specified Value: Voltage fluctuations between 100 mV and 800 mV.

=> Oxygen sensor OK.

If the oxygen sensor voltage is approx. 0 Volt, replace oxygen sensor.