Sensor and Control Check

Heated Oxygen Sensor (HO2S) and Oxygen Sensor Control After Three Way Catalytic (TWC) Converter, Checking


NOTE: When servicing terminals 3 and 4 in harness connectors of Heated Oxygen Sensor (HO2S), use only gold-plated terminals.


Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- All fuses must be OK.
- Exhaust system must be properly sealed between Three Way Catalytic (TWC) Converter and cylinder head.
- Engine Coolant temperature must be at least 85 °C, See display group 04, display field 3

Function test
- Connect VAG1551 scan tool (VAG1552). Start engine and select the Engine Control Module (ECM) using address word 01.

Connecting scan tool and selecting ECM. Refer to Scan Tool Connecting and Initial Checks. Scan Tool Testing and Procedures

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.

Indicated on display:


Read measuring value block
Enter display group number XXX


- Press -0-, -3- and -0- for the function "display group number 30", and then press -Q- to exit from input mode.

Indicated on display: (1 to 4 = display fields)


Read measuring value block 30 ->
1 2 3 4


- Check status of oxygen sensor control behind Three Way Catalytic (TWC) Converter (display field 2): Specification: 1 1 0


NOTE: The bits in display fields 2 are only set to 1 behind Three Way Catalytic (TWC) Converter temperature has risen to above 350 °C and the Engine Control Module (ECM) has recognized a partial throttle signal (See display group 43, display field 2).

Explanation of 3-digit value in display field 2:







- Display Group 30 and its evaluation

If oxygen sensor heater is not active, that is if it stays at 0:
- Test oxygen sensor heater behind Three Way Catalytic (TWC) Converter. Heater Check

If oxygen sensor or oxygen sensor control behind Three Way Catalytic (TWC) Converter is not active:

Checking primary voltage







- Disconnect 4-pin harness connector (arrow) to Oxygen Sensor (O2S) behind Three Way Catalytic (TWC) Converter -G130- behind Three Way Catalytic (TWC) Converter (bank 1).







- Use adapter cables from VAG1594 to connect multimeter to terminals 3 + 4 (Motronic ECM connector) for voltage measurement.
- Start engine and measure primary voltage. Specification: 0.40 to 0.50 volts
- Switch ignition off.

If specified value is not obtained:
- Check wires between test box and 4-pin connector to Motronic control module for open circuit according to wiring diagram.







Terminal 3 + socket 68
Terminal 4 + socket 69

Wire resistance: max: 1.5 Ohms

If specified value is obtained:
- Replace oxygen sensor behind Three Way Catalytic (TWC) Converter.

If no malfunctions are found in wires:
- Replace Engine Control Module (ECM).
- Check DTC memory, repair any malfunctions and then erase DTC memory.
- Read readiness code. If DTC memory was erased or Engine Control Module (ECM) was disconnected from continuous B+ supply, readiness code must be re-generated. Monitors, Trips, Drive Cycles and Readiness Codes Monitors, Trips, Drive Cycles and Readiness Codes