Oxygen Sensors and Sensor Regulation Before Catalytic Converter, Checking
Diagnostic Procedures
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, testers and auxiliary items 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:
• Motronic Engine Control Module (ECM) Power Supply Relay (J271) 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° 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 ] 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 ohms
- Also check wires for short circuit to B+ or Ground (GND).
Specified value: infinite 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 4: Reset/erase diagnostic data.
- Generate readiness code.