Oxygen Sensors and Control After Catalytic Converter, Checking

Oxygen Sensors and Control after Catalytic Converter, Checking

• The oxygen sensor before catalytic converter (bank 1, sensor 1 and bank 2, sensor 1) regulates to oxygen sensor 1. If this oxygen sensor is damaged, e.g. due to dirt or overheating, the regulation value may have shifted. Deviations from oxygen sensor 1 are detected by the oxygen sensor behind catalytic converter (bank 1, sensor 2 and bank 2, sensor 2). If it recognizes the deviations downward or upward, it influences the regulation before catalytic converter, generally increasing or decreasing it respectively.

Special tools, testers and auxiliary items required

• (VAG1526A)

• (VAG1594A)

• (VAG1598/31)

• (VAS5051) with (VAS5051/1)

Test requirements

• No leaks in exhaust system

• Engine coolant temperature at least 80°C => display group 004, display zone 3.

Test sequence

- Connect vehicle diagnostic, testing and information system (VAS5051) and select vehicle system "01 -Engine electronics" in selection. Refer to => [ VAS 5051, Connecting and Select Functions ] VAS 5051, Connecting and Select Functions. Engine must be running at idling speed.

Display on (VAS5051):

- Under - 1 - select diagnostic function "04 - Basic setting".

Display on (VAS5051):

1. Enter display group

- Enter "030" for "display group number 030" in zone - 2 - and confirm entry by pressing Q button.

Display on (VAS5051):

- Activate basic setting by pressing - A - button.

- Check specifications in display zones - 2 - and - 4 -.

• By increasing the engine speed the specified values are achieved more quickly.

• The "oxygen sensor status" indicates the condition of the oxygen sensor control and the oxygen sensor.

• The first digit of the 3-digit display (heating) fluctuates between 0 and 1.

• The oxygen sensor control for oxygen sensor behind catalytic converter (bank 1, sensor 2 and bank 2, sensor 2) is not active without engine load, i.e. the last digit of the 3-digit display is 0.

Display on (VAS5051):

- Continue with test if displays have reached "110" in display zones - 2 - and - 4 - at least once.

- Press arrow button.

Checking oxygen sensor control behind catalytic converter

Display on (VAS5051):

1. Enter display group max. input value = 255

- Enter "037" for "display group number 037" in zone - 2 - and confirm entry by pressing Q button.

Display on (VAS5051):

- Activate basic setting by pressing - A - button.

- Check oxygen sensor voltage in display zone - 2 -.

- Check oxygen sensor correction value in display zone- 3 - and diagnosis result in display zone - 4 -.

Note on display zone 2:

The oxygen sensor voltage Bank 1, sensor 2 should be kept as constant as possible. Strong voltage fluctuations indicate a damaged catalytic converter.

- Press arrow button.

Display on (VAS5051):

1. Enter display group

- Enter "038" for "display group number 038" in zone - 2 - and confirm entry by pressing Q button.

Display on (VAS5051):

Note on display zone 2:

The oxygen sensor voltage Bank 2, sensor 2 should be kept as constant as possible. Strong voltage fluctuations indicate a damaged catalytic converter.

- Exit function "04 - Basic setting" by pressing arrow button.

Evaluation of display groups 037 and 038

continuation

If specification in display zone 3 or 4 is not obtained:

- Perform test drive to free oxygen sensors from any possible residues and repeat test.

If specified value in display zone 3 or 4 is not obtained, even after a test drive has been performed:

- Replace relevant oxygen sensor before catalytic converter.

• If the oxygen sensor voltage is OK and after a road test the oxygen sensor correction value is still outside the specification, this indicates aging of the oxygen sensor before catalytic converter.

Checking basic voltage

- Disconnect 4-pin connector of relevant oxygen sensor behind catalytic converter, => [ Identification of connector bracket - right
side of vehicle ] Locations or => [ Identification of connector bracket - left side
of vehicle ] Locations.

- Connect multimeter between terminals 3 and 4 to measure voltage.

- Switch ignition on.

• Specified value: 0.400 to 0.500 V

- Switch ignition off.

If specified value is not obtained:

- Check oxygen sensor wiring Bank 1 , or Bank 2

If specified value is obtained:

- Replace relevant oxygen sensor behind catalytic converter.

Checking oxygen sensor wiring, Bank 1 Oxygen Sensor after Catalytic Converter

- Disconnect 4-pin connector, bank 1, Oxygen Sensor (O2S) behind three way catalytic converter (TWC) (G130) => [ Identification of connector bracket - right
side of vehicle ] Locations

- Connect test box (VAG1598/31) to wiring harness for engine control module; do not connect engine control module => [ Wiring and Component Check with Test Box VAG 1598/31 ] Wiring and Component Check With Test Box VAG 1598/31.

- Test for open circuit in following wiring connections.

- Repair open circuit, if necessary.

- Check for shorts between two wires.

If no wiring malfunction is detected:

- Replace engine control module:

• With anti-theft housing. Refer to => [ Engine Control Module with Metal Anti-Theft Housing ] Engine Control Module With Metal Anti-Theft Housing

• Without anti-theft housing. Refer to => [ Engine Control Module without Metal Anti-Theft Housing ] Engine Control Module Without Metal Anti-Theft Housing

Checking oxygen sensor wiring, Bank 2 Oxygen Sensor 2 after Catalytic Converter

- Disconnect 4-pin connector, bank 2, oxygen sensor (O2S) 2 behind three way catalytic converter (TWC) (G131) => [ Identification of connector bracket - left side
of vehicle ] Locations

- Connect test box (VAG1598/31) to wiring harness for engine control module; do not connect engine control module. Refer to => [ Wiring and Component Check with Test Box VAG 1598/31 ] Wiring and Component Check With Test Box VAG 1598/31.

- Test for open circuit in following wiring connections.