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 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.
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- Fuses in E-box (in plenum chamber, left) must be OK:
- Motronic Engine Control Module (ECM) Power Supply Relay -J271- -position A3- must be OK, check:
- Battery voltage must be at least 11.5 volts.
- All electrical consumers such as, for example, 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- position.
- 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.
- Oxygen sensor heaters for oxygen sensors before catalytic converter must be OK, check.

Function test
- Select the output of oxygen sensor signals and check whether the specified values are being reached. Diagnostic Mode 05 - Read Oxygen Sensor Monitoring Test Results
- End diagnosis and switch ignition off.

If specified values are not obtained:
- Check oxygen sensor wires according to wiring diagram.

Checking oxygen sensor wires
- Connect test box to control module wiring harness. Connecting Test Box For Wiring Test







- Disconnect 6-pin harness connector to the respective oxygen sensor:
- Heated Oxygen Sensor (HO2S) -G39-, bank 1, 6-pin harness connector -2-,
- Heated Oxygen Sensor (HO2S) 2 -G108-, bank 2, 6-pin harness connector -4-.

NOTE:
- Bank 1 = Cylinder bank 1, in direction of travel, right
- Bank 2 = Cylinder bank 2, in direction of travel, left







- Check wires between test box and 6-pin connector to Engine Control Module (ECM) for open circuit according to wiring diagram.

Wire resistance: max. 1.5 ohms.







- Also check wires for short circuit to B+ or Ground (GND).

Specified value: infinity ohms.

If no malfunctions are found in wires:
- Replace the respective oxygen sensor:
- Bank 1 Heated Oxygen Sensor (HO2S) -G39-,
- Bank 2 Heated Oxygen Sensor (HO2S) 2 -G108-.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes