Checking lambda control and lambda probe -G39 and -G108 upstream of catalytic converter — AUDI
Checking lambda control and lambda probe -G39 and -G108 upstream of catalytic converter on Audi: factory workshop procedure for engines AKC, ANK, AQF.
Workshop procedure for AUDI — the factory write-up, straight from real workshop data.
📐 20 workshop diagrams for AKC
Real factory drawings for this job — timing marks, bolt locations and routing. Locked in the free view.
📋 Procedure
AQF AQH ARU AKC AUW AVN AVP
Special tools and workshop equipment required
V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/31
VAS 5051 with VAS 5051/1
or
V.A.G 1551 with V.A.G 1551/3 A
Notes:
For specific fault finding, it is possible to switch off the lambda control by selecting display group 99 "Basic setting" mode and to switch it on again by selecting display group 99 in "Read measured value block" mode.
After selecting the display group 99 (whether in "Basic setting" or "Read measured value block" mode), it is possible to switch back and forth between the functions 04 "Basic setting" and 08 "Read measured value block" by pressing the keys 4 or 8 on V.A.G 1551.
On leaving function 04 "Basic setting", the lambda control is automatically re-activated.
Test conditions
Perform road test and do not erase fault memory.
Coolant temperature at least 85 °C.
Functional test
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 4 for the function "Initiate basic setting" and confirm entry with Q key.
Note:
During basic setting, the solenoid valve for the activated charcoal filter (valve -N80) is closed and the air conditioner compressor is switched off.
Basic setting
Enter display group number XXX
Indicated on display:
Press keys 0, 3 and 0 for "display group number 30" and confirm entry with Q key.
System in basic setting 30
⇒
1
2
3
4
Indicated on display:
(1...4 = display zones)
Check lambda probe status
(display zones 1 to 4)
Note:
The "lambda probe status" indicates the condition of the lambda control and the lambda probes.
Display zones
1 · 2 · 3 · 4
Display group 30: Lambda status at idle (coolant temperature at least 85 °C)
Display · 0 0 0 · 0 0 0
Display · Lambda probe status, bank 1, probe 1 · Lambda probe status, bank 1, probe 2 · Lambda probe status, bank 1, probe 2 · Lambda probe status, bank 2, probe 2
Range · 0 = off / 1 = on · 0 = off / 1 = on · 0 = off / 1 = on · 0 = off / 1 = on
Specified value · 1 1 1 · 1 1 1
Note: · Explanation of display => Page 24-114
Significance of 3 digit readout of display group 30
1 · 1 · 1 · Display zones 1 to 4
X · Lambda control / 0 = inactive / 1 = active
X · Lambda probe condition / 0 = inactive / 1 = active
X · Condition of lambda probe heating / 0 = inactive / 1 = active
Checking lambda probe learned values and lambda control
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 4 for the function "Initiate basic setting" and confirm entry with Q key.
Note:
During basic setting, the solenoid valve for the activated charcoal filter (valve -N80) is closed and the air conditioner compressor is switched off.
Basic setting
Enter display group number XXX
Indicated on display:
Press keys 0, 3 and 3 for "display group number 33" and confirm entry with Q key.
System in basic setting 33
⇒
1
2
3
4
Indicated on display:
(1...4 = display zones)
Check lambda control
(display zones 1 to 4):
Display zones
1 · 2 · 3 · 4
Display group 33: Lambda control at idle
Display · xx.x % · x.xxx volts · xx.x % · x.xxx V
Display · Lambda control / bank 1 · Lambda probe voltage, bank 1 · Lambda control / bank 2 · Lambda probe voltage, bank 2
Range · min.: -25.0 % / max.: 25.0 % · min.: 0 V / max.: 1.000 V · min.: -25.0 % / max.: 25.0 % · min.: 0 V / max.: 1.000 V
Specified value · In range / -10.0...10.0 % the value must be at least / 2 % · In range 0.000...1.000 volts, the voltage must fluctuate · In range / -10.0...10.0 % the value must be at least / 2 % · In range 0.000...1.000 volts, the voltage must fluctuate
Note · If the specification is not attained =>Page 24-91 · If the specification is not attained, see evaluation =>Page 24-94 · If the specification is not attained =>Page 24-91 · If the specification is not attained, see evaluation =>Page 24-94
Press the Ckey.
Press keys 0, 3 and 2 for "display group number 32" and confirm entry with Q key.
System in basic setting 32
⇒
1
2
3
4
Indicated on display:
(1...4 = display zones)
Check lambda control
(display zones 1 to 4):
Display zones
1 · 2 · 3 · 4
Display group 32: Lambda probe learned values at idle
Display · xx.x % · xx.x % · xx.x % · xx.x %
Display · Lambda learned value / bank 1, probe 1 / at idle / (additive) · Lambda learned value / bank 1, probe 1 / on part throttle / (multiplicative) · Lambda learned value / bank 1, probe 2 / at idle / (additive) · Lambda learned value / bank 1, probe 2 / on part throttle / (multiplicative)
Range · min.: -25.0 % / max.: 25.0 % · min.: -25.0 % / max.: 25.0 % · min.: -25.0 % / max.: 25.0 % · min.: -25.0 % / max.: 25.0 %
Specified value · -5.7...5.7 % / can fluctuate slightly · -15.0...15.0 % / can fluctuate slightly · -5.7...5.7 % / can fluctuate slightly · -15.0...15.0 % / can fluctuate slightly
Note · If the specification is not attained =>Page 24-93 · If the specification is not attained =>Page 24-93 · If the specification is not attained =>Page 24-93 · If the specification is not attained =>Page 24-93
If specification is not attained in display zone 1 or display zone 3 (display group 33), or if the value does not fluctuate by at least 2%:
Check intake system for leaks and rectify unmetered air
Check the lambda probe heating
=>Page
24-114
.
Check lambda probe signal wiring and actuation => Page
24-122
Check fuel pressure regulator => Page
24-39
Fuel return line kinked or blocked.
Press ⇒key.
Press keys 0 and 6 for the "End output" function and press the Q key to confirm entry.
Switch ignition off.
Evaluation of display group 32
Display group 32
Display zone: 1 to 4 · Possible causes of fault · Fault remedy
Lambda learned values in range / -5.7 to -25.0 % · - Oil dilution · - Carry out oil change or drive vehicle fairly fast on out-of-town roads
Display zone: 2 / 4 · - High oil consumption
Lambda learned values in range / -15.0 to -25.0 % · - Air mass meter defective · - Test air mass meter / =>Page . 24-65
- Solenoid valve for activated charcoal filter stuck open · - Check solenoid valve for activated charcoal filter => Page . 24-157
- Fuel pressure too high / - Fuel return line kinked or blocked. · - Check fuel pressure regulator / =>Page . 24-39 / Check fuel return line
- Injector leaking · - Check injectors =>Page 24-48
Evaluation of display group 32
Display group 32
Display zone: 1 to 4 · Possible causes of fault · Fault remedy
Lambda learned values in range / 5.7 to 25.0 % · - Unmetered air in intake area · - Check intake system for leaks and rectify unmetered air
/ Display zone: 2 / 4 · - Fuel pressure too low · - Check fuel pressure regulator / =>Page . 24-39
Lambda learned values in range / 15.0 to 25.0 % · - Lambda probe heating defective · - Check lambda probe heating / =>Page . 24-114
- Injector only opens partially or not at all · - Check injectors =>Page 24-48
- Solenoid valve for activated charcoal filter stuck open · - Check solenoid valve for activated charcoal filter => Page . 24-157
Evaluation of display group 33
Display group 33
Display zone: 2 / 4 · Possible causes of fault · Fault remedy
approx. 0.450 V · - Open circuit in wire 4 between lambda probe and control unit · - Check signal wiring and actuation => Page 24-122
- Open circuit in wire 3 between lambda probe and control unit
- Lambda probe heating defective / - Lambda probe defective · - Checking lambda probe heating =>Page . 24-114 / Fit a new lambda probe
Greater than 1.100 V · - Short to positive in wire 4 between lambda probe and control unit · - Check lambda probe wiring for bank 1, lambda probe 1 => Page 24-123
Less than 0.100 V · - Short to earth in wire 4 between lambda probe and control unit / - Short circuit between wires 3 and 4 · - Check lambda probe wiring for bank 2, lambda probe 1 => Page 24-128
TorqFix answers live for your specific car — tell it the engine code and it serves the matching sequence, torque figures and wiring for that exact variant.
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Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.
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The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.