With Manufacturer's Scan Tool

Oxygen Sensor (O2S) and oxygen sensor control before Three Way Catalytic Converter (TWC), checking

Special tools and equipment
- V.A.G 1551 Scan Tool (or VAG 1552 mobile scan tool) with VAG 1551/3 cable
- VAG 1598/31 test box
- VAG 1526 multimeter or VAG 1715 multimeter
- VAG 1594 connector test kit
- Wiring diagram

Test requirements

- Fuse no.34 must be OK.
- Coolant temperature must be at least 80°C, See Display group 04, display field 3
- Exhaust system must be properly sealed between catalytic converter and cylinder head.

Function test

- Connect V.A.G 1551 scan tool (VAG 1552). Start engine and select Engine Control Module (ECM) using address word 01. Refer to Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting V.A.G 1551 Scan Tool Testing and Inspection

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 HELP
Input display group number XXX

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

Indicated on display (1 - 4 = display fields)

Read Measuring Value Block 30 ->
1 2 3 4

- Check status of oxygen sensor control before catalytic converter (display fields 1 and 3):
Specification: 111, display group 30 and its evaluation. Refer to Scan Tool Testing/Measuring Value Blocks (Function 08)/Evaluating Display Groups 30-44, 99 Testing and Inspection

If the expected value(s) are not obtained:
- Test oxygen sensor heater before catalytic converter. With Manufacturer's Scan Tool

If specified values are obtained:
- Change to display group 32 as follows:
- Press -C- button.

Indicated on display

Read Measuring Value Block
Input display group number XXX

- Press 0, 3 and 2 for the function "display group number 32", and then press Q to exit from input mode.

Indicated on display (1 - 4 = display fields)

Read Measuring Value Block 32 ->
1 2 3 4

- Check idle oxygen sensor adaptation values (additive) in display fields 1 and 3.
Specification: -10.0 to 10.0%

- Check partial throttle oxygen sensor adaptation values (multiplicative) in display fields 2 and 4.
Specification: -10.0 to 10.0%

If the expected value(s) are not obtained: Refer to Scan Tool Testing/Measuring Value Blocks (Function 08)/Evaluating Display Groups 30-44, 99 Testing and Inspection

If specified values are obtained:
- Change to display group 33 as follows:

V.A.G 1551: Press button -3-
VAG 1552: up arrow key is pressed

Indicated on display (1 - 4 = display fields)

Read Measuring Value Block 33 ->
1 2 3 4

- Observe oxygen sensor control in display fields 1 and 3.

The indication should oscillate in the range from -10.0 to 10.0% by at least 2%.

- Check oxygen sensor voltage in display fields 2 and 4.

The voltage should oscillate at least 20 times a minute in the range from 0 to 1.0 V.

If one or more of the indications in display field 2 or 4 is constant on one value:
- Continue testing according to following table.

If oxygen sensor control in display fields 1 or 3 does not oscillate in specified range:
- Press -> button.
- Press buttons -0- and -6- to select "End data transfer" function 06. Press -Q- button to confirm input.
- Free Heated Oxygen Sensor (HO2S) with a road test and repeat test.

Observe safety precautions which apply to road tests.

If expected values are not obtained even after a road test, that is if oxygen sensor control does not oscillate by at least 2%:
- Switch ignition off.
- Replace appropriate Heated Oxygen Sensor (HO2S).

Checking Primary Voltage

- Unplug 4-pin harness connector going to corresponding Heated Oxygen Sensor (HO2S):

Heated Oxygen Sensor (HO2S) -G39-, bank 1 before catalytic converter 4-pin harness connector (black) (arrow).

Heated Oxygen Sensor (HO2S) 2 -G108-, bank 2 before catalytic converter 4-pin harness connector (black) (arrow).

To get at this harness connector, remove coolant container attachment screws and tilt coolant container to the side. The coolant hoses can remain connected.

- Use auxiliary wires from VAG 1594 to connect multimeter with terminals 3 + 4 of appropriate 4-way connector (going to control module) to make voltage measurement.
- Switch ignition on and measure primary voltage.
Specification: 0.40-0.50 V

- Switch ignition off.

If expected value is not obtained on one or both Heated Oxygen Sensors (HO2S):
- Test oxygen sensor wires.

If specified values are obtained:
- Replace appropriate Heated Oxygen Sensor (HO2S) before catalytic converter.

Checking Oxygen Sensor Wires

- Connect VAG 1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.

- Check for wire breaks between test box and 4-way connector (going to control module) (see wiring diagram). For Heated Oxygen Sensor (HO2S) -G39-, bank 1 before catalytic converter use following:
Terminal 3 + socket 51
Terminal 4 + socket 70
Wire resistance: max. 1.5 Ohms

- For Heated Oxygen Sensor (HO2S) 2 -G108-, bank 2 before catalytic converter use following:
Terminal 3 + socket 12
Terminal 4 + socket 13
Wire resistance: max. 1.5 Ohms

- Check for shorts to ground in wires on the two 4-way connectors (going to control module) at terminals 3 + 4 (see wiring diagram).
Terminal 3 + socket 32
Terminal 4 + socket 32
Wire resistance: infinity Ohms

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

If no malfunctions are found in wires:
- Replace Engine Control Module (ECM).