Checking lambda probe heating -Z29 for lambda probe downstream of catalytic converter — AUDI

Special tools and workshop equipment required

V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/31

Test requirements:

Coolant temperature at least 80 °C.

Fuse for lambda probe heating OK.

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

Test sequence

Unplug 4-pin connector -1- (brown) to lambda probe downstream of catalytic converter -G130.

Note:

To gain access to the connector screw out coolant expansion tank bolts and move expansion tank to side. Fuel hoses remain connected.

Connect multimeter between contacts 1 and 2 to measure resistance.
Specified value at room temperature 6.4...47.5 ω

If specified value is not attained:

Replace lambda probe downstream of catalytic converter -G130.

If specified value is attained:

Check the voltage supply to the lambda probe heating.

Checking voltage supply for lambda probe heating

Connect multimeter between contacts 1 (positive) and 2 (earth) to measure voltage.
Start the engine.
Specified value: approx. battery voltage

Note:

Points at which lambda probe heating is switched on and off by engine control unit can be observed in "Reading measured value block" function, display group number 041, display zone 4.

If no voltage is present:

Connect multimeter as follows to measure voltage:

Connector / Contact · Measure at
1 (positive) · Vehicle earth

Operate starter briefly.
Specified value: approx. battery voltage

If again no voltage is present:

Check the wiring from contact 1 on the connector via the fuse to the fuel pump relay for an open circuit:

=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder

If voltage supply is OK:

Connect multimeter as follows to measure voltage:

Connector / Contact · Measure at
2 (earth actuation by engine control unit) · Battery positive

Start the engine.
Specified value: approx. battery voltage, may fluctuate

Switch ignition off.

If no voltage is present:

Connect test box V.A.G 1598/31 to wiring harness for engine control unit; do not connect the engine control unit => Page
24-19
.

Check for open circuit in the following wiring connections:

Connector / Contact · Test box V.A.G 1598/31 / Socket
2 · 63

Rectify open circuit, if necessary.

If wiring is OK but there is no earth connection for the lambda probe heating:

Replace engine control unit => Page
24-24
.