Testing lambda probe heating — AUDI

APR
Note:

The lambda probe heating circuit is monitored by the self-diagnosis system.

Interrogate fault memory => Page
01-9
.

Connect vehicle diagnostic, testing and information system VAS 5051 (or fault reader V.A.G 1551) and select engine electronics control unit by entering address word "01" ( => Page
01-3
.)
When doing this the engine must be idling.

Rapid data transfer
HELP
Select function XX
Indicated on display:

Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Read measured value block
Enter display group number XXX
Indicated on display:

Press keys 0, 4 and 1 for "Display Group 41" and confirm entry with Q key.

Read measured value block 41
⇒
1
2
3
4
Indicated on display:

Check resistance of lambda probe heating.

Display zones
1 · 2 · 3 · 4
Display Group 41: Lambda probe heating, Bank 1 (at idling speed)
Display · x.xx Kω · Htg.bC.ON
Indicates · Bank 1, Probe 1 · Status of heating
Range · min.: 0 Kω / max.: 100 Kω · Htg.bC.ON / Htg.bC.OFF · /
Specification · less than2 Kω · Htg.bC.ON
Note

Press key C.
Press keys 0, 4 and 2 to select "Display Group 42" and confirm entry with Q key.

Display zones
1 · 2 · 3 · 4
Display Group 42: Lambda probe heating, Bank 2 (at idling speed)
Display · x.xx Kω · Htg.bC.ON
Indicates · Bank 2, Probe 1 · Status of heating
Range · min.: 0 Kω / max.: 100 Kω · Htg.bC.ON / Htg.bC.OFF · /
Specification · less than2 Kω · Htg.bC.ON
Note

If the specification is not attained:

Test voltage supply for lambda probe heating
=> Page
24-82
.

Testing voltage supply for lambda probe heating

Test fuse for lambda probe heating

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

Connect hand-held multimeter (voltage measurement range) between sockets 1 (positive) and 2 (earth) using test leads from V.A.G 1594.
Operate the starter briefly.

Specification: approx. battery voltage

If there is no voltage reading:

Connect hand-held multimeter (voltage measurement range) between socket 1 (positive) and vehicle earth using test leads from V.A.G 1594.
Operate the starter briefly.

Specification: approx. battery voltage

If there is still no voltage reading:

Test for open circuit and/or short circuit in wiring between fuel pump relay and socket 1 on the relevant lambda probe connector (on wiring harness) via fuse.

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

If the voltage supply is OK:

Connect hand-held multimeter (voltage measurement range) between socket 2 (switched earth connection from engine control unit) and battery positive terminal using test leads from V.A.G 1594.
Start the engine.

Specification: approx. battery voltage (fluctuating)

Note:

At certain points in the operating range the engine control unit continuously "switches" the earth connection to the lambda probe heating. In other words, it repeatedly makes and breaks the earth connection at these points. For this reason the voltage reading on the tester may fluctuate.

Switch off ignition.

If there is no voltage reading:

Connect test box V.A.G 1598/31 to wiring harness for engine control unit. Do not connect to the engine control unit itself.
=> Page
24-14
.

Test for open circuits in the following wiring connection:

Lambda probe, Bank 1 -G39

Connector on wiring harness, socket · Test box V.A.G 1598/31, socket
2 · 5

Lambda probe, Bank 2 -G108

Connector on wiring harness, socket · Test box V.A.G 1598/31, socket
2 · 4

Resistance in wiring: max. 1.5 ω

=> Current flow diagrams, Electrical fault finding and Fitting locations binder

If the wiring is OK but the lambda probe heating still has no earth connection:

Fit a new engine control unit => Page
24-17
.