Sensor and Control Check
Oxygen Sensor And Oxygen Sensor Control Before Catalytic Converter, Checking
Special tools and equipment
- V.A.G 1551 scan tool (or VAG 1552 mobile scan tool) with VAG 1551/3B cable
- VAG 1598/31 adapter cable
- VAG 1526 multimeter or VAG 1715 multi meter
- VAG 1594 connector test kit
- Wiring diagram
Test requirements
- 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 the Engine Control Module (ECM) using address word 01. (connecting scan tool and selecting ECM). Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/Connecting VAG 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
Enter display group number XXX
- Press buttons -0-, -3- and -0- to select "Display group number 30". Press -Q- button to confirm input.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 30 ->
1 2 3 4
- Check status of oxygen sensor control before catalytic converter (display field 1): Specification: x 11
NOTE: The sensor heater is pulsed by the Engine Control Module (ECM). This is why the indication for the sensor heater alternates between 0 and 1.
Explanation of 3-digit value in display field 1:
If oxygen sensor heater is not active:
- Test oxygen sensor heater before catalytic converter. Heater Check
If oxygen sensor or oxygen sensor control is not active:
- Test oxygen sensor wires
Additionally, for engine code ATW:
- Check oxygen sensor voltage
If specified value is obtained:
- Change to display group 32 as follows:
- Press -C- button.
- Press buttons -0-, -3- and -2- to select "Display group number 32". Press -Q- button to confirm input.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 32 ->
1 2 3 4
- Check oxygen sensor adaptation values (additive) at idle in display field 1. Specification: -10.0 to 10.0 %
- Check oxygen sensor adaptation values (multiplicative) at partial throttle in display field 2. Specification: -10.0 to 10.0 %
If specified value is not obtained:
- Evaluation display group 32. Refer to "Scan Tool Testing/Measuring Value Blocks (Function 08)/Evaluating Measured Value Blocks/Evaluating Display Groups 30 to 49, 99", Testing and Inspection
If specified value is obtained:
- Change to display group 33 as follows: V.A.G 1551 Scan Tool (ST): Press buttons -3- and -3- VAG 1552 mobile scan tool: Press up arrow button.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 33 ->
1 2 3 4
- Observe oxygen sensor control in display field 1. Indication should oscillate in the range from -10.0 to 10.0 % by at least 2 %.
If specified value is not obtained:
- 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 the safety precautions that apply to road tests.
If specified value in display field 1 is not obtained even after road test or if value does not fluctuate at least 2 %:
- Replace Heated Oxygen Sensor (HO2S) -G39-.
Checking oxygen sensor voltage
- Check the oxygen sensor voltage in display field 2. Voltage must oscillate at least 20 times per minute in the range from 0 to 1.0 volts.
If indication in display field 2 remains constant on one value:
- Continue testing according to the following table.
Indicated Cause
Between 0.400 and Open circuit
0.500 volts
1.105 V Short circuit to B+
0.000 V Short circuit to Ground (GND)
Checking primary voltage
- Disconnect 4-pin harness connector (black) to Heated Oxygen Sensor (HO2S) - G39- (item no.1).
- Use adapter cables from VAG1594 to connect multimeter to terminals 3+4 (ECM connector) for voltage measurement.
- Switch on ignition and measure primary voltage. Specification: 0.40 to 0.50 volts
- Switch ignition off.
If specified value is not obtained:
- Test oxygen sensor wires.
If specified value is obtained:
- Replace Heated Oxygen Sensor (HO2S) -G39-.
Checking oxygen sensor wires
- Connect VAG 1598/31 adapter cable to control module wiring harness. Engine Control Module (ECM) is not connected.
- Check wires between test box and 4-pin connector (to control module) for open circuit according to wiring diagram.
Terminal 3 + socket 51
Terminal 4 + socket 70
Wire resistance: max: 1.5 Ohms
- Check wires at connector terminal 3+4 for short circuit to terminal 1+2 according to diagram.
If no malfunctions are found in wires:
- Replace Heated Oxygen Sensor (HO2S) -G39-.