Testing operation of lambda probes: Audi 2.8 (ACK, ALG)

ALG
Special tools, testers and auxiliary items

Fault reader V.A.G 1551 (or vehicle system tester V.A.G 1552) with cable V.A.G 1551/3

Connect fault reader V.A.G 1551
=> Page
01-3
.
Start the engine.
Select "Read measured value block", Display Group 003, engine at idling speed=>Page
01-115
.

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

Do not proceed with the test until the coolant temperature shown in display zone 3 has reached at least 80°C.

Press C key.
Press keys 0, 0 and 9 for Display Group 009 and confirm entry with Q key.

Read measured value block 9
⇒
1
2
3
4
Indicated on display:

Display zone 1 will show the signal voltage for lambda probe 1.

Display zone 2 will show the signal voltage for lambda probe 2.

If the lambda probe voltage reading fluctuates very slowly, test the lambda probe heating => Page
24-72
.
If the display shows a constant lambda probe voltage reading of 0.000 V, this means there is a short circuit to earth.
Test wiring => Page
24-72
.
If the display shows a constant lambda probe voltage reading of between 0.45 and 0.50 V, this means there is an open circuit in the signal wire. Test wiring => Page
24-74
.
If the display shows a constant lambda probe voltage reading of 1.105 V, this means there is a short circuit to positive.
Test wiring=>Page
24-74
.
If the display shows a constant voltage reading of between 0.0 and +0.3 V (mixture too lean), this means that the lambda control has reached the maximum enrichment limit but the lambda probe is still registering "Mixture too lean".

If the display shows a constant voltage reading of between +0.7 and 1.0 V (mixture too rich), this means that the lambda control has reached the maximum leaning-down limit but the lambda probe is still registering "Mixture too rich".
Press C key.

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

If the lambda probe is functioning properly, select Display Group 008 and check lambda learned values.
=>Page
01-127
.

Read measured value block 8
⇒
1
2
3
4
Indicated on display:

Display zone 3 will show the lambda learned value for cylinder bank 1. Display zone 4 will show the lambda learned value for cylinder bank 2.

The lambda control has learning ability, i.e. is self-adaptable. Faults such as unmetered air or defective injectors have the effect of changing the air/fuel mixture composition. The lambda probes detect this and compensate by adjusting the basic injection periods mapped in the control unit. The injection periods are extended or reduced until a mixture composition of λ = 1 is achieved. The difference between the actual injection period and the basic period mapped in the control unit is given as a percentage.

Positive learned value (+...%): Pre-programmed basic injection period is too short, actual injection period is ...%longer in order to achieve "λ= 1" mixture composition.
Negative learned value (-...%): Pre-programmed basic injection period is too long, actual injection period is ...%shorter in order to achieve "λ= 1" mixture composition.

Specifications: Reading measured value block => Page
01-128
.

If the values do not match the specifications, see test table for Display Group 007=>Page
01-126
.

Note:

If necessary, Display Group 007 can also be checked and printed out in the "Basic setting" mode (function 04) for the purposes of fault-finding. In the "Basic setting" mode the influence of systems such as the activated charcoal filter is eliminated=>Page
01-86
.