Oxygen Sensors And 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 and workshop equipment required
- Multimeter VAG1526 or multimeter VAG1715
- Connector test kit VAG1594
- Wiring diagram
Test requirements
- Fuses in E-box (in plenum chamber, left) must be OK: Refer to SYSTEM WIRING DIAGRAM
- Motronic Engine Control Module (ECM) Power Supply Relay -J271- must be OK, check: Refer to SYSTEM WIRING DIAGRAM
- 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° C, Diagnostic mode 1: Check measured values; PID 5, Coolant temperature.
- Oxygen sensor heaters for oxygen sensors before catalytic converter must be OK, check OXYGEN SENSOR HEATER BEFORE CATALYTIC CONVERTER, CHECKING .
Function test
-- Select the output of oxygen sensor signals 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 oxygen sensor wires according to wiring diagram.
Checking oxygen sensor wires
-- Connect test box to control module wiring harness, connect 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-.
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 Ω
| Component | Connector | Test box |
|---|---|---|
| Bank 1 sensor 1 | Terminal 1 | Socket 70 |
| Terminal 2 | Socket 71 | |
| Terminal 5 | Socket 51 | |
| Terminal 6 | Socket 52 | |
| Bank 2 sensor 1 | Terminal 1 | Socket 13 |
| Terminal 2 | Socket 14 | |
| Terminal 5 | Socket 12 | |
| Terminal 6 | Socket 15 |
-- Also check wires for short circuit to B+ or Ground (GND).
Specified value: ∞ Ω
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 4: Reset/erase diagnostic data.
-- Generate readiness code.