Checking lambda probe heating before catalytic converter — AUDI

Special tools, workshop equipment, testers, measuring instruments and auxiliary items required

Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
Test box V.A.G 1598/31
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Adapter set V.A.G 1594
Current flow diagram

Check conditions

Fuses for Lambda probe must be OK.

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

The battery voltage must be at least 11.5 V.
Fuel pump relay must be OK

Test sequence

Connect the vehicle diagnostic, testing and information system VAS 5051 => Page
01-13
, and select the vehicle system "01 - Engine electronics" from the menu. When doing this the ignition must be on.

Display on VAS 5051:

Select diagnosis function "08 - Read data block" from the menu -1-.

Display on VAS 5051:

1 -
Enter display group
(figures up to 255)

Using the keypad -2-, enter display group number 041 and confirm entry with the Q button.

Display on VAS 5051:

Check the status of the lambda probe heating in display zone 2:
Display: Htg.bC.ON

Note:

The Lambda probe heating may be switched on or off depending on the operating mode of the engine, therefore the display in display zone 2 may show "Htg.bC.ON or alternating from Htg.bC.ON to Htg.bC.OFF.

If the specification is not obtained:

Unplug the 6-pin connector (black) for lambda probe before catalytic converter (G39).

Check whether the pin identification is the same on both connectors (connector going to lambda probe and connector going to engine control unit). Note the instructions in the following test.
Test procedure if identification is not the same:

Connect multimeter (resistance test range) between contacts 3 and 4.

Specification at room temperature: 2.5 ... 10 ω

Test procedure if identification is the same:

Connect multimeter (resistance test range) between contacts 1 and 2.

Specification at room temperature: 2.5 ... 10 ω

If specification is not obtained:

Replace Lambda probe before catalytic converter (G39).

If specification is obtained:

Set multimeter to measure voltage and connect to contacts 1 and 2 on connector to control unit.
Start engine and run at idling speed.
Measure the voltage supply:
When display group 41, display zone 2 displays
Display, Htg.bC.ON:
Specification: 11.0...14.5 V
Display, Htg. bC.ON/Htg.bC.OFF (alternating)
Specification: Between 0.0...12.0 V fluctuating
Switch off ignition.

If no voltage is present:

Connect test box V.A.G 1598/31 to control unit wiring harness. The engine control unit remains disconnected => Page
24-8
.

Check wiring for open circuit between test box and 6-pin connector using current flow diagram.
Contact 1+socket 5
Wire resistance: Max. 1.5 ω

If the specification is obtained:

Check wiring from contact 2 to fuel pump relay (J17) using current flow diagram.

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