Oxygen Sensor and Sensor Regulation Before Catalyst, Checking

Oxygen sensor and oxygen sensor regulation before catalytic converter, checking

Recommended special tools and equipment
- V.A.G 1526 multimeter or V.A.G 1715 multimeter
- V.A.G 1594 connector test kit
- Wiring diagram

Test requirements

- The respective fuses of Heated Oxygen Sensor (HO2S) -G39- must be OK.
- Battery voltage must be at least 11.5 Volts.
- All electrical consumers such as, lights and rear window defroster must be switched off.
- Parking brake must be engaged or else daylight driving lights will be switched on.
- For vehicles with automatic transmission, selector lever must be in -P-.
- If vehicle is equipped with an A/C system, it must be switched off.
- Ground (GND) connections between engine and chassis must be OK.
- Exhaust system must be properly sealed between catalytic converter and cylinder head.
- Coolant temperature must be at least 80°C, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.
- Oxygen sensor heater for oxygen sensor before catalytic converter must be OK.

Test sequence

- Select the lambda test results and check whether specified values are being reached, Diagnostic mode 5: Check output of oxygen sensor signals.

If specified values are obtained:

- End diagnosis and switch ignition off

If specified values are not obtained:

- End diagnosis and let engine continue to run at idle
- Check primary voltage.

Checking primary voltage

- Disconnect 4-pin harness connector (black) to Heated Oxygen Sensor (HO2S) -G39- (item no. 1)

Vehicles > 08.99

- Connect multimeter for voltage measurement to terminals 3 + 4 of connector to Engine Control Module (ECM) and measure primary voltage.
Specified value: 0.400 to 0.500 Volts

Continue for all vehicles

- Switch ignition off.

If specified value is not obtained:
- Test oxygen sensor wires.

If specified value is obtained:
- Replace Heated Oxygen Sensor (HO2S) 1 -G39- bank 1 before catalytic converter.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.

Checking oxygen sensor wires
- Connect test box to control module wiring harness, connect test box for wiring test.

Vehicles > 08.99

- Check wires between test box and 4-pin connector (to control module) for open circuit according to wiring diagram.
Terminal 3 + socket 42
Terminal 4 + socket 20
Wire resistance: max. 1.5 Ohms

- Check wires for short circuit to B+ and to Ground (GND).
Specified value: Infinite Ohms

Vehicles 09.99 >

- Check wires between test box and 4-pin connector (to control module) for open circuit according to wiring diagram.
Terminal 3 + socket 25
Terminal 4 + socket 26
Wire resistance: max. 1.5 Ohms

- Check wires for short circuit to B+ and to Ground (GND).
Specified value: Infinite Ohms

Continue for all vehicles

If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) 1 -G39- bank 1 before catalytic converter.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.