Oxygen Sensor and Oxygen Sensor Control Before Catalytic Converter, Checking
Oxygen Sensor And Oxygen Sensor Control Before Catalytic Converter, Checking
NOTE:
- Vehicle must be raised before connector for oxygen sensor is accessible.
- When servicing terminals in harness connector of oxygen sensor, use only gold-plated terminals.
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
Requirements
- The respective fuse 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.
- 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 degrees C => page ST-18. Diagnostic mode 1: Check measured values; PID 5, Coolant temperature. Diagnostic Mode 1: Check Measured Values
- Oxygen sensor heater for oxygen sensor before catalytic converter must be OK, check => page 24-64.
Function test (Vehicles with engine code AEG)
- Select output of oxygen sensor signals and check whether specified values are being reached => page ST-31. Diagnostic mode 5: Check output of oxygen sensor signals.
- End diagnosis and switch ignition off.
If specified values are not obtained:
- Check primary voltage => page 24-177.
Checking primary voltage
- Remove protective cover (arrows) and disconnect 4-pin harness connector (black) -1- to Heated Oxygen Sensor (HO2S) G39- before catalytic converter.
- Connect multimeter to terminals 3 + 4 of connector to Engine Control Module (ECM) for voltage measurement.
- Switch on ignition and measure primary voltage.
Specified value: 0.400 to 0.500 Volts
- Switch ignition off.
If specified value is not obtained:
- Test oxygen sensor wires => page 24-179.
If specified value is obtained:
- Replace Heated Oxygen Sensor (HO2S) -G39-.
- Erase DTC memory of Engine Control Module (ECM) => page ST-29. Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
Checking oxygen sensor wires
- Connect test box to control module wiring harness => page ST-11. connect test box for wiring test. Test Box, Connecting For Wiring Test
- 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
If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) -G39-.
- Erase DTC memory of Engine Control Module (ECM) => page ST-29. Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
Function test (Vehicles with engine code AVH, AZG, BDC, BEV, BGD)
NOTE: The oxygen sensor before catalytic converter has a static regulation and can be differentiated from the oxygen sensor behind catalytic converter via a 6-pin connector.
- Select output of oxygen sensor signals and check whether the specified values are being reached => page ST-31. Diagnostic mode 5: Check output of oxygen sensor signals.
- End diagnosis and switch ignition off.
If specified values are not obtained:
- Test oxygen sensor wires => page 24-180.
Checking oxygen sensor wires
- Connect test box to control module wiring harness => page ST-11. connect test box for wiring test. Test Box, Connecting For Wiring Test
- Remove protective cover (arrows) and disconnect 6-pin harness connector (black) -1- to Heated Oxygen Sensor (HO2S) G39- before catalytic converter.
- Check wires between test box and 6-pin connector (to control module) for open circuit according to wiring diagram.
Terminal 1 + socket 70
Terminal 2 + socket 71
Terminal 5 + socket 51
Terminal 6 + socket 52
Wire resistance: max. 1.5 Ohms
- Check wires for short circuit to B+ and to Ground (GND).
Specified value: Infinite Ohms
If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) -G39-.
- Erase DTC memory of Engine Control Module (ECM) => page ST-29. Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes