Audi Workshop Service and Repair Manuals

Note:

Lambda control downstream of catalytic converter is on a higher level than lambda control upstream of catalytic converter and provides corrective action.

The lambda probe downstream of the catalytic converter also corrects slight shifts in the mixture (e.g towards rich) by causing lambda control upstream of catalytic converter to dwell at its upper/lower point for a certain period.

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

Test requirements:

• ● Test drive performed and fault memory not erased
• ● Coolant temperature at least 80 °C=>Display group 004, display zone 3

Test sequence

• ‒ Connect vehicle diagnostic, testing and information system VAS 5051 or fault reader V.A.G 1551 and select engine electronics control unit with "address word" 01 .
  Engine must be idling.

• ‒ Enter "04" for "Start basic setting" function and confirm with Q key.

Note:

During basic setting activated charcoal filter solenoid valve -N80 is closed and air conditioner compressor switched off.

• ‒ Enter "043" for "Display group number 043" and confirm with Q key.

• ‒ By pressing accelerator, increase engine speed to approx. 3000 rpm until display zone 2 shows a temperature well in excess of 350 °C. Then release accelerator pedal so that engine runs at idling speed.
• ‒ Set engine speed with engine-speed setting tool V.A.G 1788/10 to 1800...2200 rpm.
• ‒ Press and hold brake pedal until display in zone 4 switches from "Test OFF" to "Test ON".
• ‒ Continue to maintain engine speed at 1800...2200 rpm and keep brake pedal pressed until result of diagnosis appears in display zone 4.

Note on display zone 2:

Value calculated from engine speed and engine load.

Continued

If reading does not match specification in display zone 4:

• ‒ Perform test drive to remove any residue from lambda probe and repeat test.

If reading in display zone 4 does not match specification even after a test drive:

• ‒ Check basic voltage => Page 24-108
• ‒ Check wiring of lambda probe downstream of catalytic converter
  => Page 24-110

Checking basic voltage

• ‒ → Unscrew protective cover -arrows- on underside of vehicle.

• ‒ → Unplug 4-pin connector -1- (brown) for lambda probe downstream of catalytic converter -G130.

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

If reading does not match specification:

• ‒ Check lambda probe wiring => Page 24-110.

If reading matches specification:

• ‒ Replace lambda probe downstream of catalytic converter -G130.

Checking lambda probe wiring

• ‒ → Unscrew protective cover -arrows- on underside of vehicle.

• ‒ → Unplug 4-pin connector -1- (brown) for lambda probe downstream of catalytic converter -G130.
• ‒ Connect test box V.A.G 1598/31 to engine control unit wiring harness. Actual engine control unit is not to be connected.

• ‒ → Check for open circuit in the following wiring.

• ‒ Eliminate open circuit in wiring if necessary.
• ‒ Check wiring for mutual short circuit.

If wiring is OK:

• ‒ Replace engine control unit => Page 24-16.