Audi Workshop Service and Repair Manuals

Checking Lambda probe heater -Z19- for Lambda probe -G39- Special tools and workshop equipment required t  -V.A.G 1526 A- t  -V.A.G 1594 A- t  -V.A.G 1598/31-

Test sequence   Note t  Coolant temperature at least 80 °C t  Fuse for Lambda probe heating OK → Current flow diagrams, Electrical fault finding and Fitting locations

–  Unscrew the protective cover -arrows-. –  Unplug the 6-pin connector (black) to the Lambda probe -G39-.

–  Connect up the multimeter (resistance measuring range) between contacts 3 and 4. t  Specification: 2.5 ... 10 Ω (at room temperature) If the reading does not match the specification: –  Replace the Lambda probe -G39-. If the reading matches the specification: –  Check voltage supply for Lambda probe heating. Checking voltage supply for Lambda probe heater -Z19-

–  Connect up the multimeter (voltage measuring range) between contacts 3 and 4. –  Start engine. t  Specification: approx. battery voltage   Note The point at which the engine control unit switches the Lambda probe heating on and off can be observed if applicable in the “Reading measured value block” function, display group number 041, display zone 2. If there is no voltage:

–  Connect up the multimeter (voltage measuring range) as follows.

Connector Contact	Measure to
3 (positive)	Vehicle earth

–  Briefly operate the starter. t  Specification: approx. battery voltage If there is still no voltage: –  Check for open circuit in the wiring from contact 3 of the connector via the fuse to the fuel pump relay: If the voltage supply is OK:

–  Connect up the multimeter (voltage measuring range) as follows:

Connector Contact	Measure to
4 (engine control unit switched earth connection)	Battery positive

–  Start engine. t  Specification: approx. battery voltage   Note The point at which the engine control unit switches the Lambda probe heating on and off can be observed if applicable in the “Reading measured value block” function, display group number 041, display zone 2. –  Switch off ignition. If there is no voltage: –  Connect the test box -V.A.G 1598/31- to the wiring harness to the engine control unit, but do not connect the actual engine control unit → Chapter.

–  Check for open circuit in the following wiring:

Connector Contact	Test box -V.A.G 1598/31- Socket
4	5

–  Eliminate open circuit in wiring if necessary. → Current flow diagrams, Electrical fault finding and Fitting locations If the wiring is OK but there is no earth supply for the Lambda probe heating: –  Replace the engine control unit → Chapter.