Testing lambda probe and lambda control (after catalytic converter) - not on vehicles with engine code letters AJQ, AQA — AUDI

APP AQA ARZ
Special tools and workshop equipment required

V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/31
V.A.G 1788/10
VAS 5051 with VAS 5051/1

or

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

Notes:

The lambda control after catalytic converter governs the lambda control before catalytic converter and regulates variations in the control values.

If the air/fuel mixture provided by the lambda probe before catalytic converter deviates slightly from the required value (e.g. mixture too rich), the lambda probe after catalytic converter maintains the voltage signal transmitted by the lambda probe before catalytic converter at minimum/maximum for a certain period (control period). If the voltage signal is held in the positive range (e.g. 50 ms), the air/fuel mixture is enriched, if it is held in the negative range (e.g. -50ms), the air/fuel mixture is leaned down.

The 4-pin connectors for lambda probes and lambda probe heaters are accessible after unscrewing -arrows- the connector cover -2- from the underside of the vehicle (right side).

Colour coding of connectors:
Black for lambda probe (before catalytic converter) -G39 and lambda probe heater -Z19;
Brown for lambda probe after catalytic converter -G130 and lambda probe 1 heater, after catalytic converter -Z29.

Requirements for test:

Take the car for a test drive and do not erase the fault memory.
Coolant temperature at least 80 °C

Test sequence

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:

Enter "04" to select "Basic setting" and confirm with Q key.

Note:

During the basic setting the activated charcoal filter solenoid valve (ACF valve -N80) is closed and the air conditioner compressor is switched off.

Basic setting
Q
Enter display group number XXX
Indicated on display:

Enter "030" to select Display Group 030 and confirm entry with Q key.
Set an engine speed of 1800...2200 rpm using speed regulator V.A.G 1788/10:

Note:

The lambda control of the lambda probe after catalytic converter (B1-S2) is not actuated without engine load.

System in basic setting
30
⇒
1
2
3
4
Indicated on display:

Check status of lambda probe (after catalytic converter) in display zone 2.

Notes:

It can take some minutes to perform this process.
The "lambda probe status" indicates the state of the lambda control and of the lambda probe.

Display zones
1 · 2 · 3 · 4
Display Group 030: Lambda probe status at idling speed
Display · X X X · X X X
Display · Lambda probe status Bank 1, Probe 1 · Lambda probe status Bank 1, Probe 2
Range · 0 = off / 1 = on · 0 = off / 1 = on · /
Specification · 1 1 1 · 1 1 0
Note · If readout does not match specification => Page . 24-83

Note:

The first digit of the three digit display (lambda probe heating) jumps between 0 and 1.

Relevance of 3-figure display in Display Group 030

X · X · X · Display zone 2
1 · Lambda control active
1 · Lambda probe condition
1 · Status of lambda probe heating

Testing basic voltage

Remove connector cover -arrows-.,

Unplug 4-pin connector (brown) for lambda probe (after catalytic converter) -G130.

Connect multimeter (voltage measurement range) between contacts 3 and 4.
Switch ignition on.
Specification: 0.400 ... 0.500 V

Switch off ignition.

If the specification is not obtained:

Test lambda probe wiring.

If the specification is obtained:

Renew lambda probe after catalytic converter.

Testing lambda probe wiring

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
24-19
.
Test the following wiring connections for open circuits:

Connector / Contact · Test box V.A.G 1598/31 / Socket
3 · 68
4 · 69

Rectify any open circuits.
Test for short circuits between the wires.

If the wiring is OK:

Fit a new engine control unit => Page
24-21
.