Oxygen Sensors and Oxygen Sensor Regulation Before Catalytic Converter, Checking
Diagnostic Procedures
Oxygen Sensors and Oxygen Sensor Regulation Before Catalytic Converter, Checking
• When servicing terminals in harness connector of oxygen sensors, use only gold-plated terminals.
• The oxygen sensors before catalytic converter have a constant regulation and can be differentiated from the oxygen sensor behind catalytic converter via a 6-pin connector.
Special tools, testers and auxiliary items required
• Hand multimeter (V.A.G 1526) or Multimeter (V.A.G 1715)
• Test adapter kit (V.A.G 1594)
• Wiring diagram
Test Conditions
• Motronic Engine Control Module (ECM) Power Supply Relay 2 (J670) -position 5- must be OK, check:
• Battery voltage (both batteries) must be at least 11.5 Volts.
• All electrical consumers such as, lights and rear window defroster must be switched off.
• For vehicles with automatic transmission, selector lever must be in " P".
• Parking brake must be engaged.
• The Ground (GND) connections between engine and body 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 01 - Read Current System Data ] Diagnostic Modes 01 - 09, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.
• Oxygen sensor heaters for oxygen sensors before catalytic converter must be OK, checking => [ Oxygen Sensor Heaters Before Catalytic Converter, Checking ].
• Fuses in right instrument panel fuse holder must be OK:
Right instrument panel fuse holder
Function Test
- Select the oxygen sensor test results and check whether the specified values are being reached => [ Diagnostic Mode 05 - Read Oxygen Sensor Monitoring Test Results ] Diagnostic Modes 01 - 09, Diagnostic mode 5: Check oxygen sensor test results.
- End diagnosis and switch ignition off.
If the specifications are not obtained:
- Check oxygen sensor wires to control module according to wiring diagram.
Checking Oxygen Sensor Wires to Control Module
Cylinder bank 1
- Connect test box to Engine Control Module (ECM) (J623) wiring harness on connecting test box for wiring test, refer to Repair Manual,
Cylinder bank 2
- Connect test box to Engine Control Module (ECM) 2 (J624) wiring harness on connecting test box for wiring test, refer to Repair Manual,
Cylinder bank 1 and 2
- Disconnect corresponding 6-pin harness connector to the oxygen sensor to be tested: Component location
• Cylinder bank 1 with cylinders 1 through 6 is located at right in direction of travel.
• Cylinder bank 2 with cylinders 7 through 12 is located at left in direction of travel.
- Check wires between test box and 6-pin connector to Engine Control Module for open circuit according to wiring diagram. Wiring resistance: max. 1.5 ohms
Oxygen sensor connector
- Check wires for short circuit to B+ and Ground (GND). Specification: infinite ohms
If no malfunction is detected in the wiring:
- Replace respective oxygen sensor:
• Heated Oxygen Sensor (HO2S) (G39), refer to Repair Manual.
• Heated Oxygen Sensor (HO2S) 2 (G108),
• Heated Oxygen Sensor (HO2S) 3 (G285),
• Heated Oxygen Sensor (HO2S) 4 (G286),
- Erase DTC memory of Engine Control Module (ECM) => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09, Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.
Oxygen Sensors and Oxygen Sensor Regulation after Catalytic Converter, Checking
• When servicing terminals 3 and 4 in harness connector of oxygen sensors, use only gold-plated terminals.
Special tools, testers and auxiliary items required
• Hand multimeter (V.A.G 1526) or Multimeter (V.A.G 1715)
• Test adapter kit (V.A.G 1594)
• Wiring diagram
Test Conditions
• Motronic Engine Control Module (ECM) Power Supply Relay (J271) -position 4- must be OK, check:
• Battery voltage (both batteries) must be at least 11.5 Volts.
• All electrical consumers such as, lights and rear window defroster must be switched off.
• For vehicles with automatic transmission, selector lever must be in " P".
• Parking brake must be engaged.
• The Ground (GND) connections between engine and body 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 01 - Read Current System Data ] Diagnostic Modes 01 - 09, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.
• Oxygen sensor heaters for oxygen sensors behind catalytic converter must be OK, checking => [ Oxygen Sensor Heaters After Catalytic Converter, Checking ].
• Fuses in right instrument panel fuse holder must be OK:
Right instrument panel fuse holder
Function Test
- Select oxygen sensor test results and check whether specified values are being reached => [ Diagnostic Mode 05 - Read Oxygen Sensor Monitoring Test Results ] Diagnostic Modes 01 - 09, Diagnostic mode 5: Check oxygen sensor test results.
- End diagnosis and switch ignition off.
If specifications are not obtained:
- Check oxygen sensor wires to control module according to wiring diagram.
Checking oxygen sensor wires to control module
Cylinder bank 1
- Connect test box to Engine Control Module (ECM) (J623) wiring harness on connecting test box for wiring test, refer to Repair Manual,
Cylinder bank 2
- Connect test box to Engine Control Module (ECM) 2 (J624) wiring harness on connecting test box for wiring test, refer to Repair Manual,
Cylinder bank 1 and 2
- Disconnect corresponding 6-pin harness connector to oxygen sensor to be tested: Component location
• Cylinder bank 1 with cylinders 1 through 6 is located at right in direction of travel.
• Cylinder bank 2 with cylinders 7 through 12 is located at left in direction of travel.
- Check wires between test box and 4-pin connector to Engine Control Module for open circuit according to wiring diagram. Wiring resistance: max. 1.5 ohms
- Check wires for short circuit to B+ and Ground (GND). Specification: infinite ohms
If no malfunction is detected in the wiring:
- Replace respective oxygen sensor:
• Oxygen Sensor (O2S) Behind Three Way Catalytic Converter (TWC) (G130).
• Oxygen Sensor (O2S) 2 Behind Three Way Catalytic Converter (TWC) (G131).
• Oxygen Sensor (O2S) 3 Behind Three Way Catalytic Converter (TWC) (G287).
• Oxygen Sensor (O2S) 4 Behind Three Way Catalytic Converter (TWC) (G288).
- Erase DTC memory of Engine Control Module => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09, Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.