Oxygen Sensor and Oxygen Sensor Control Before Catalytic Converter, Checking
Oxygen Sensor (O2S) And Oxygen Sensor Control Before Three Way Catalytic Converter (TWC), Checking
NOTE:
- Vehicle must be raised before connector for oxygen sensor is accessible.
- When servicing terminals in harness connector of Heated Oxygen Sensor (HO2S), use only gold-plated terminals.
Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 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 like, for example, lights and rear window heating 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 position -P- or -N-.
- 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 degree C, Diagnostic mode 1: Check measuring values; PID 5, Coolant temperature. Diagnostic Mode 1: Check Measured Values
- Oxygen sensor heater for oxygen sensor before catalytic converter must be OK, check.
Function test (Vehicles with engine code AEG)
- Select the oxygen sensor test results and check whether the specified values are being reached, Diagnostic mode 5: Check output of oxygen sensor signals.
- End diagnosis and switch ignition off.
If specified values are not obtained:
- Check primary voltage.
Checking primary voltage
- Unscrew 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.
If specified value is obtained:
- Replace Heated Oxygen Sensor (HO2S) 1 Bank 1 -G39- before catalytic converter, item 9.
- Erase DTC memory of Engine Control Module (ECM),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, connect test box 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
- Also check wires for short circuit to B+ and Ground (GND).Specified value: infinite ohms
If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) 1 Bank 1 -G39- before catalytic converter, item 9.
- Erase DTC memory of Engine Control Module (ECM), 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)
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 the lambda test results and check whether the specified values are being reached, Diagnostic mode 5: Check output of oxygen sensor signals. Diagnostic Mode 5: Check Output of Oxygen Sensor Signals
- End diagnosis and switch ignition off.
- Test oxygen sensor wires.
Checking oxygen sensor wires
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test
- Unscrew 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
- Also check wires for short circuit to B+ and Ground (GND). Specified value: Infinite Ohms
If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) 1 Bank 1 -G39- before catalytic converter, item 5.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes