Checking operation of lambda probes — AUDI

Special tools, testers and auxiliary items required

VAS 5051 with VAS 5051/1

or

V.A.G 1551 with V.A.G 1551/3 A

Test sequence

Reading measured value block, display group 001, engine at idling speed=>Page
01-100
.

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

Do not proceed with the test until the coolant temperature shown in display zone 1 has reached at least 85 °C.

Press C key.
Enter "010" for "Display group number 010" and confirm entry with Q key.

Read measured value block 10
⇒
1
2
3
4
Indicated on display:

Display zone 3 will show the signal voltage for lambda probe 1.

Display zone 4 will show the signal voltage for lambda probe 2.

If the lambda probe voltage fluctuates very slowly, check the lambda probe heating => Page
24-81
.
If the display shows a constant lambda probe voltage reading of 0.000 V, this means there is a short circuit to earth; check wiring => Page
24-81
.
If a constant lambda probe voltage of 0.35 ... 0.45 V is displayed, there is an open circuit in the signal wiring; check the wiring => Page
24-84
.
If the display shows a constant lambda probe voltage reading of 2.550 V, this means there is a short circuit to earth; check wiring => Page
24-84
.
If the display shows a constant voltage reading of 0.0 - +0.3 V (mixture too lean), this means that the lambda control has reached the control stop in the "enrich" direction, but the lambda probe is still registering "Mixture too lean".

If the display shows a constant voltage reading of +0.6 - 1.0 V (mixture too rich), this means that the lambda control has reached the control stop in the "lean" direction, but the lambda probe is still registering "Mixture too rich".
Press C key.

Reading measured value block
Q
Enter display group number XXX
Indicated on display:

If the lambda probe is functioning properly, select display group 005/006 and check the lambda learned values =>Page
01-116
.

Read measured value block 5
⇒
1
2
3
4
Indicated on display:

Display zone 1 will show the lambda learned value at idle for cylinder bank 1.

Read measured value block 6
⇒
1
2
3
4
Indicated on display:

Display zone 1 will show the lambda learned value at idle 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 programmed in the maps. The injection periods are extended or reduced until a "λ = 1" mixture composition is achieved. The difference between the actual injection period and the basic period programmed in the map is given as a percentage.

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

Specifications: Reading measured value block => Page
01-130
.

If the specifications are not obtained: Test table display group 007 =>Page
01-124

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. This function excludes, for example, the influence of the ACF =>Page
01-80
.