Checking lambda probe heating for lambda probes — AUDI

AQF AQH ARU AKC AUW AVN AVP
Note:

The lambda probe heating circuit is monitored by the self-diagnosis system, interrogate fault memory => Page
01-21
.

Connect the vehicle diagnostic, testing and information system VAS 5051 or fault reader V.A.G 1551 and select engine electronics control unit 1 with "Address word" 01 => Page
01-15
.
For this purpose, the engine must be running at idling speed.

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 number 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 · xxx kOhm · Htg. u.c.c. ON · xxx kOhm · Htg. d.c.c. ON
Display · Bank 1, probe 1 · Condition of lambda probe heating upstream of catalytic converter · Bank 1, probe 2 · Condition of lambda probe heating downstream of catalytic converter
Range · Htg. u.c.c. ON / Htg. u.c.c. OFF · Htg. d.c.c. ON / Htg. d.c.c. OFF
Specified value · Smaller than 2 kOhm · Htg. u.c.c. ON · Smaller than 2 kOhm · Htg. d.c.c. ON
Note · It may take a few minutes until specified value is attained

Press the Ckey.
Press keys 0, 4 and 2 for "display group number 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 · xxx kOhm · Htg. u.c.c. ON · xxx kOhm · Htg. d.c.c. ON
Display · Bank 1, probe 2 · Condition of lambda probe heating upstream of catalytic converter · Bank 2, probe 2 · Condition of lambda probe heating downstream of catalytic converter
Range · Htg. u.c.c. ON / Htg. u.c.c. OFF · Htg. d.c.c. ON / Htg. d.c.c. OFF
Specified value · Smaller than 2 kOhm · Htg. u.c.c. ON · Smaller than 2 kOhm · Htg. d.c.c. ON
Note · It may take a few minutes until specified value is attained

If specified value is not attained:

Check the voltage supply to the lambda probe heating => Page
24-117
.
Check lambda probe signal wiring and actuation => Page
24-122
.

Check voltage supply for lambda probe heating

Fitting locations of 4-pin connectors for lambda probes => Page
24-6
.

Check fuse for lambda probe heating.

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

Disconnect 4-pin connector of relevant lambda probe.

Using leads from V.A.G 1594, connect hand-held multimeter (voltage measurement range) to sockets 1 (positive) and 2 (earth).
Operate starter briefly.

Specified value: approx. battery voltage

If no voltage is present:

Using leads from V.A.G 1594, connect hand-held multimeter (voltage measurement range) to socket 1 (positive) and vehicle earth.

Operate starter briefly.

Specified value: approx. battery voltage

If no voltage is present:

Check the wiring from socket 1 on the relevant lambda probe connector on the wiring harness via the fuse to the fuel pump relay for open circuit or short.

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

If the power supply is OK:

Using leads from V.A.G 1594, connect hand-held multimeter (voltage measurement range) to socket 2 (earth actuation from engine control unit) and battery positive.

Start the engine.

Specified value: approx. battery voltage, fluctuating

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.

Switch ignition off.

If no voltage is present:

Connect test box V.A.G 1598/31 to wiring harness for engine control unit; do not connect the engine control unit => Page
24-12
.
Check for open circuit in the following wiring connections:

Lambda probe upstream of catalytic converter: Bank 1 -G39

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

Lambda probe upstream of catalytic converter: Bank 2 -G108

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

Lambda probe downstream of catalytic converter: Bank 1 -G130

Connector on wiring harness, socket · Test box V.A.G 1598/31 socket
2 · 63 (earth)

Lambda probe downstream of catalytic converter: Bank 2 -G131

Connector on wiring harness, socket · Test box V.A.G 1598/31 socket
2 · 6 (earth)

Wire resistance: max. 1.5 Ohm

Rectify open circuit, if necessary.

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

If wiring connections are OK.

Replace appropriate lambda probe.