Oxygen Sensors and Oxygen Sensor Regulation Before Catalytic Converter, Checking
Oxygen Sensors And Oxygen Sensor Regulation Before Catalytic Converter, Checking
NOTE: 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
Test requirements
- The respective fuses of Heated Oxygen Sensor (HO2S) -G39- and Heated Oxygen Sensor (HO2S) 2 -G108- 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. Diagnostic mode 1: Check measured values; PID 5, Coolant temperature. Diagnostic Mode 1: Check Measuring Values
- Oxygen sensor heaters for oxygen sensors before catalytic converter must be OK, check.
Function test
- Select the following output of oxygen sensor signals 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
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 to the respective oxygen sensor:
Heated Oxygen Sensor (HO2S) -G39-, 4-pin harness connector (black, arrow).
Heated Oxygen Sensor (HO2S) 2 -G108-, 4-pin harness connector (black, arrow).
NOTE: To reach this harness connector, remove coolant reservoir attachment screws and tilt coolant reservoir to the side. The coolant hoses remain connected.
- Connect multimeter for voltage measurement to terminals 3 + 4 of the respective connector to Engine Control Module (ECM) and measure primary voltage.
Specified value: 0.40 to 0.50 Volts
- Switch ignition off.
If specified value is not obtained on one or both Heated Oxygen Sensors (HO2S):
- Test oxygen sensor wires
If specified values are obtained:
- Replace the respective oxygen sensor:
- Heated Oxygen Sensor (HO2S) -G39- before catalytic converter
- Heated Oxygen Sensor (HO2S) 2 -G108- before catalytic converter.
- 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
Checking oxygen sensor wires
- Connect test box to control module wiring harness. connect test box for wiring test. Test Box, Connecting For Wiring Test
- Check wires between test box and 4-pin connector to Engine Control Module (ECM) for open circuit according to wiring diagram.
Wire resistance: max. 1.5 ohms
Vehicles with engine code AHA
Vehicles with engine code AHA
Continuation for all vehicles
- Also check wires for short circuit to B+ and to Ground (GND).
Specified value: Infinite ohms
If no malfunctions are found in wires:
- Replace Motronic Engine Control Module (ECM) -J220-.