Checking lambda probe heating for primary 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 6-pin connector to relevant lambda probe upstream of catalytic converter.
Connect multimeter between contacts 3 and 4 to measure resistance.

Specified value at room temperature: 2.5...4.4 ω

When the engine is at operating temperature, the resistance is increased by approx. 4...6 ω.

If specified value is not attained:

Replace appropriate lambda probe upstream 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 3 and 4 of corresponding primary catalytic converter lambda probe 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 the function "Reading measured value block", display group number 041/042, display zone 2.

If no voltage is present:

Connect multimeter as follows to measure voltage.

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

Operate starter briefly.
Specified value: approx. battery voltage

If no voltage is present:

Check the wiring from contact 3 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
4 (earth actuation by engine control unit) · Battery positive

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 the function "Reading measured value block", display group number 041/042, display zone 2.

Switch ignition off.

If no voltage is present:

Connect test box V.A.G 1598/31 to wiring harness for engine control unit 1; do not connect the engine control unit => Page
24-31
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Check for open circuit in the following wiring connections:

Connector -G39 (bank 1 probe 1) / Contact · Test box V.A.G 1598/31 / Socket
4 · 5

Connector -G108 (bank 2 probe 1) / Contact · Test box V.A.G 1598/31 / Socket
4 · 4

Rectify open circuit, if necessary.

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

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

Replace engine control unit 1
=>Page
24-38
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