Testing rear window heater signal — AUDI
Testing rear window heater signal on Audi: factory workshop procedure for engines ABZ, AEW, AHC, AKG. Full factory text, tools and checks.
Workshop procedure for AUDI — the factory write-up, straight from real workshop data.
📐 18 workshop diagrams for ABZ
Real factory drawings for this job — timing marks, bolt locations and routing. Locked in the free view.
📋 Procedure
AEW AHC AKG AKJ AKH
Note
Switching on the rear window heater connects a positive signal to contact C22 of the engine control unit.
Engine code ABZ
(model years 1994, 1995 and 1996):
Connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit=>Page
01-2
.
Start engine.
Gear selector to Neutral (automatic gearbox)
Switch off air conditioner.
Read measured value block (function 08) and select Display Group 03=>Page
01-106
Read measured value block 3
⇒
1
2
3
4
Display:
Do not continue the test until the coolant temperature in display zone 3 is at least 80°C.
Press C key.
Read measured value block (function 08) and select Display Group 05=>Page
01-111
.
Read measured value block 5
⇒
1
2
3
4
Display:
Display zone 1: Actual speed
Display zone 2: Specified speed
Switch on rear window heater.
Note:
The specified idling speed is only reached after the accelerator is pressed once (with gear engaged).
See idling speed table
=>Page
01-112
.
If the specified value is not reached, check the signal wire for the rear window heater=>Page
24-118
.
Engine code ABZ / AKJ from model year 1997
Engine code AEW / AHC / AKJ / AKH
Connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit=>Page
01-2
.
Start engine.
Gear selector in Neutral (automatic gearbox)
Switch off air conditioner.
Read measured value block (function 08) and select Display Group 03=>Page
01-106
Read measured value block 3
⇒
1
2
3
4
Display:
Do not continue the test until the coolant temperature in display zone 3 is at least 80°C.
Press C key.
Read measured value block (function 08) and select Display Group 24=>Page
01-138
.
Read measured value block 24
⇒
1
2
3
4
Display:
Display zone 4: "Rear.wn.h.OFF"
Switch on rear window heater.
Display zone 4: "Rear.wn.ht. ON"
Switch off engine.
If the specified value is not reached, check the signal wire for the rear window heater.
Testing signal wire for rear window heater
Connect test box V.A.G 1598/19 to engine control unit wiring harness=>Page
24-15
.
Connect diode test lamp between socket D11 (earth) and C22.
Switch on ignition and rear window heater.
The diode test lamp should light up when the rear window heater is switched on.
If diode test lamp does not light up, check for open circuit in wiring from contact C22 on engine control unit to rear window heater switch.
=> Current Flow Diagrams, Electrical Fault-Finding and Fitting Locations binder
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.
Ask about my car →Other AUDI procedures
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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.
Seen a figure that does not match your manual? Write to us — we correct it and note when. support@torqfix.com
The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.