Checking lambda probe heating for post catalytic converter lambda probes (cylinders 1 to 6) — AUDI

Fitting locations overview =>
24-5

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

Disconnect 4-pin connector to relevant lambda probe downstream of catalytic converter.

Connect multimeter between contacts 1 and 2 to measure resistance.
Specified value at room temperature: 1.0 ... 20.0 ω

If specified value is not attained:

Replace appropriate lambda probe downstream of catalytic converter.

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:

At certain operating points, the engine control unit "cycles" the earth for the lambda probe heating. This means that at these points, the earth is continuously switched on and off. For this reason, the voltage reading on the tester may fluctuate.

If no voltage is present:

Connect multimeter as follows to measure voltage:

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

Operate starter briefly.
Specified value: approx. battery voltage

If 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 to
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 1; the engine control unit should not be connected =>Page
24-31
.

Check for open circuit in the following wiring connections:

Connector -G130 (bank 1 probe 2) / Contact · Test box V.A.G 1598/31 / Socket
2 · 63

Connector -G131 (bank 2 probe 2) / Contact · Test box V.A.G 1598/31 / Socket
2 · 6

Rectify open circuit, if necessary.

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

Replace engine control unit => Page
24-38
.