Audi Workshop Service and Repair Manuals

Note:

The lambda probe before catalytic converter (Bank 1, Probe 1) holds the value atlambda = 1. If the function of this lambda probe is impaired due to dirt or overheating, the controlled value can alter. The lambda probe after catalytic converter (Bank 1, Probe 2) detects any deviations from lambda = 1. It corrects variations (positive or negative) by increasing or reducing the lambda control before catalytic converter accordingly.

Special tools and workshop equipment required

• ◆ V.A.G 1526 A
• ◆ V.A.G 1594 A
• ◆ V.A.G 1598/31
• ◆ V.A.G 1788/10
• ◆ VAS 5051 with VAS 5051/1

• or

• ◆ V.A.G 1551 with V.A.G 1551/3 A

Requirements for test:

• ● Exhaust system free of leaks
• ● Coolant temperature at least 80 °C

Test sequence

• ‒ Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551) and select engine electronics control unit by entering address word "01" ( .)
  When doing this the engine must be idling.
• ‒ Apply engine speed regulator V.A.G 1788/10 to accelerator pedal and set engine speed to 2600 rpm.

Test requirement:

• ● Engine running at 2600 rpm

• ‒ Enter "04" to select "Basic setting" and confirm with Q key.

• ‒ Enter "030" to select Display Group 030 and confirm entry with Q key.
• ‒ Check lambda probe status in display zone 2.

Note:

The "lambda probe status" display indicates the status of the lambda control and lambda probes.

Notes:

• ◆ The first digit of the three-digit display (heating) fluctuates between 0 and 1.
• ◆ The lambda control of lambda probe (after the catalytic converter; B1-P2) is not active when the engine is not running under load.

• ‒ Do not continue test until display "110" is indicated in display zone 2 at least once.

Testing lambda control (after catalytic converter)

Test requirement:

• ● Engine still running at 2600 rpm

• ‒ Press C key.

• ‒ Enter "037" for Display Group 037 and confirm entry with Q key.

• ‒ Check lambda probe voltage in display zone 2:
• ‒ Check the lambda compensating value in display zone 3 and the result of the diagnosis in display zone 4.

Note on display zone 2:

The lambda probe voltage (Bank 1, Probe 2) should remain more or less constant. Large voltage fluctuations indicate that the catalytic converter is damaged.

Reading Display Group 037

Further notes

If the readout in display zone 3 or 4 does not match the specification:

• ‒ Take car for a test drive to free lambda probe of any deposits, then repeat the test.

If the readout in display zone 3 or 4 still does not match the specification even after the test drive:

• ‒ Replace the lambda probe (before the catalytic converter) -G39.

Note:

If the lambda probe voltage is OK and the compensating value is still above 0.02 even after a test drive, this points to excessive ageing of the lambda probe before catalytic converter.

Testing basic voltage

• ‒ → Unplug 4-pin connector (brown) for lambda probe (after catalytic converter) -G130.

Note:

For access to connector, unscrew bolts securing coolant expansion tank and pivot expansion tank clear to the side. The coolant hoses do not have to be disconnected.

• ‒ → Connect multimeter (voltage measurement range) between contacts 3 and 4.
• ‒ Switch ignition on.
• ‒ Specification: 0.400 ... 0.500 V
• ‒ Switch off ignition.

If the specification is not obtained:

• ‒ Test lambda probe wiring.

If the specification is obtained:

• ‒ Replace the lambda probe (after catalytic converter) -G130.

Testing lambda probe wiring

• ‒ → Unplug 4-pin connector (brown) for lambda probe (after catalytic converter) -G130.

Note:

For access to connector, unscrew bolts securing coolant expansion tank and pivot expansion tank clear to the side. The coolant hoses do not have to be disconnected.

• ‒ Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
  => Page 24-10.

• ‒ → Test the following wiring connections for open circuits:

• ‒ Rectify any open circuits.

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

• ‒ Test for short circuits between the wires.

If the wiring is OK:

• ‒ Fit a new engine control unit => Page 24-13.