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Checking lambda probe heating > < Testing lambda control (engine codes:APT, ARG)

A4 Mk1

Motronic injection and ignition system (4-cyl.)
Testing lambda control (engine codes:APT, ARG)
Testing lambda probe and lambda control

Notes:

  • ◆ For the purposes of fault-finding it is possible to switch off the lambda control by selecting Display Group 99 in "Basic setting" mode and to switch it on again by selecting Display Group 99 in "Read measured value block" mode.
  • ◆ After selecting Display Group 99 (either in "Basic setting" mode or in "Read measured value block" mode) it is possible to switch back and forth between function 04 ("Basic setting") and function 08 "Read measured value block") by pressing keys 4 and 8 on fault reader V.A.G 1551.
  • ◆ When exiting the "Basic setting" mode (function 04) the lambda control is automatically switched on again.

Test conditions

  • ● Take the car for a test drive and do not erase the fault memory.
  • ● Coolant temperature at least 85 °C

Testing operation

  • ‒ 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" ( .)
    When doing this the engine must be idling.
 
→ Indicated on display:
Rapid data transfer    HELP
Select function XX
  • ‒ Press keys 0 and 4 for the function "Introduction of basic setting" and confirm entry with the 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.
 
→ Indicated on display:
Basic setting
Enter display group number XXX
  • ‒ Press keys 0, 3 and 0 to select Display Group 30 and confirm entry with the Q key.
 
→ Indicated on display:
(1...4 = display zones)
Basic setting 30    ⇒
    1    2    3    4
  • ‒ Check lambda probe status
    (display zone 1).

Note:

The "Lambda probe status" display indicates the status of the lambda control and lambda probes.

Display zones

1

2

3

4

Display Group 30: Lambda probe status at idling speed (coolant temperature at least 85°C)

Display

0 0 0

Indicates

Lambda probe status

Range

0 = off
1 = on


Specification

1 1 1

Note

- Explanation of the display => Page 24-76

Relevance of 3-figure display in Display Group 30

X

X

X

Display zone 1

X

Lambda control
0= inactive
1= active

X

Lambda probe condition
0= inactive
1= active

X

Status of lambda probe heating
0= inactive
1= active

Testing lambda probe learned values and lambda control

  • ‒ Press key C.
  • ‒ Press keys 0, 3 and 2 to select Display Group 32 and confirm entry with the Q key.
 
→ Indicated on display:
(1...4 = display zones)
Basic setting 32    ⇒
    1    2    3    4
  • ‒ Take vehicle for a test drive (about 10 minutes).
Important:
Secure fault reader to rear seat and operate from this location. When doing this, always observe the relevant safety precautions => Page 24-1.
  • ‒ Check lambda control
    (display zones 1 and 2):

Display zones

1

2

3

4

Display Group 32: Lambda learned values with engine idling

Display

xx.x %

xx.x %

Indicates

Lambda learned value at idling speed
(additive)

Lambda learned value at part throttle
(multiplicative)

Range

min.: -25.0 %
max.: 25.0 %

min.: -25.0 %
max.: 25.0 %

Specification

-10.0...10.0 %
can fluctuate slightly

-10.0...10.0 %
can fluctuate slightly

Note

If readout does not match specification

If readout does not match specification

If specification is met:

  • ‒ Press key C.
  • ‒ Press keys 0, 3 and 3 to select Display Group 33 and confirm entry with the Q key.
 
→ Indicated on display:
(1...4 = display zones)
System in basic setting 33    ⇒
    1    2    3    4
  • ‒ Check lambda control
    (display zones 1 and 2):

Display zones

1

2

3

4

Display Group 33: Lambda control at idling speed

Display

xx.x %

x.xxx V

Indicates

Lambda control

Lambda probe voltage

Range

min.: -25.0 %
max.: 25.0 %

min.: 0.000 V
max.: 1.000 V

Specification

Within -10.0...10.0% range, value should fluctuate by at least
2 %.

Within 0.000...1.000 V range, voltage should fluctuate.

Note

If specification is not met

If specification is not met

If the readout in display zone 1 does not match the specification, or if the readout does not fluctuate by at least 2 %:

  • ‒ Take car for a test drive to free lambda probe of any deposits, then repeat the test.

If the readout in display zone 1 still does not match the specification even after the test drive, or if the readout still does not fluctuate by at least 2 %:

  • ‒ Test the lambda probe heating
    => Page 24-72.
  • ‒ Test the lambda probe signal wiring and activation => Page 24-76.
  • ‒ Check intake system for air leaks and rectify as necessary.
  • ‒ Press ⇒key.
  • ‒ Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
  • ‒ Switch off the ignition.

Reading Display Group 32

Display Group 32

Display zones 1 / 2

Possible cause of fault

Fault remedy

Lambda learned
values between
-10.0 and -25.0 %

- Oil dilution

- Carry out oil change or drive car
at moderate to high speeds on
out-of-town roads

- High oil consumption

- Air mass meter defective

- Test air mass meter
=> Page 24-43

- Solenoid valve for activated charcoal filter sticking in open position

- Test solenoid valve for activated charcoal filter => Page 24-131

- Fuel pressure too high

- Test fuel pressure regulator
=> Page 24-20

- Injector leaking

- Test injectors => Page 24-31

Reading Display Group 32

Display Group 32

Display zones 1 / 2

Possible cause of fault

Fault remedy

Lambda learned
values between
10.0 and 25.0 %

- Unmetered air in intake tract

- Check intake system for leaks and eliminate unmetered air

- Fuel pressure too low

- Test fuel pressure regulator
=> Page 24-20

- Lambda probe heating defective

- Test lambda probe heating
=> Page 24-72

- Injector not opening or only opening partially

- Test injectors => Page 24-31

- Solenoid valve for activated charcoal filter sticking in open position

- Test solenoid valve for activated charcoal filter => Page 24-131

Reading Display Group 33

Display Group 33

Display zone 2

Possible cause of fault

Fault remedy

Approx. 0.450 V

- Open circuit in wire 4 between lambda probe and control unit
- Open circuit in wire 3 between lambda probe and control unit

- Test signal wire and activation => Page 24-76

- Lambda probe heating defective

- Lambda probe defective

- Check lambda probe heating
=> Page 24-72
Renew lambda probe

Higher than 1.100 V

- Short to positive in wire 4 between lambda probe and control unit

- Test lambda probe wiring
=> Page 24-77

Less than 0.100 V

- Short to earth in wire 4 between lambda probe and control unit

- Test signal wire and activation => Page 24-76

Checking lambda probe heating > < Testing lambda control (engine codes:APT, ARG)