Audi Workshop Service and Repair Manuals

Checking voltage supply for lambda probe heating

–  Connect the multimeter for voltage measurement range (direct voltage) between contact 3 and contact 4. –  Start the engine. t  Specification: 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 2. If no voltage is present:

–  Connect up multimeter as follows to measure voltage.

Connector Contact	Measure against
3 (positive)	Vehicle earth

–  Operate the starter briefly. t  Specification: approx. battery voltage If no voltage is present: –  Check for open circuit from contact 3 of connector via fuse to fuel pump relay: → Current flow diagrams, Electrical fault finding and Fitting locations If voltage supply is OK:

–  Connect multimeter as follows to measure voltage:

Connector Contact	Measure against
4 (earth actuation by engine control unit)	Battery positive

–  Start the engine. t  Specification: 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 2. –  Switch off ignition. If no voltage is present: –  Connect test box -V.A.G 1598/31- to wiring harness for engine control unit. Do not connect engine control unit → Chapter.

–  Check for open circuit in the following wiring connections:

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

–  Rectify open circuit, if necessary. If wiring is OK but there is no earth connection for the lambda probe heating: –  Replace engine control unit → Chapter.