Oxygen Sensor Heater Before Catalytic Converter, Checking
Diagnostic Procedures
Oxygen Sensor Heater before Catalytic Converter, Checking
• When servicing terminals in harness connector of oxygen sensors, use only gold-plated terminals.
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.
Test sequence
- 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.
Checking voltage supply and wiring to control module
- Connect multimeter to terminals 3 + 4 of connector to Engine Control Module (ECM) for voltage measurement.
- Start engine, and let run at idle.
Specified value: at least 7.0 V
If specified value is obtained:
- Switch ignition off.
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.
If specified value is not obtained:
- Connect multimeter to terminal 3 of connector to Engine Control Module (ECM) + Ground (GND) for voltage measurement.
Specified value: at least 11.0 V
- Switch ignition off.
If specified value is not obtained:
- Check voltage supply at 6-pin connector terminal 3 to Motronic Engine Control Module (ECM) Power Supply Relay (J271) according to wiring diagram:
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.
If specified value is obtained:
- Check Ground (GND) activation of the respective oxygen sensor heater.
Checking Ground (GND) activation of oxygen sensor heating
- Connect test box to control module wiring harness , connect test box for wiring test.
- Check wires between test box and 6-pin connector to Engine Control Module (ECM) for open circuit according to wiring diagram.
Wire resistance: max. 1.5ohms
- Also check wires for short circuit to B+ or Ground (GND).
Specified value: infinite ohms
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.
If no malfunctions are found in wires:
- Replace Motronic Engine Control Module (ECM) (J220).