Rear Window Defogger Signal, Checking

NOTE:
- The Engine Control Module (ECM) receives a positive (+) voltage signal at terminal C22 when the rear window defogger is switched on.


Test conditions
- Vehicle at room temperature, greater than 15 °C (59 °F)
- Engine Coolant Temperature (ECT) at least 85 °C (185 °F)
- ECM coding OK
- Transmission selector lever in Neutral position
- Rear window defogger switched off

- Connect VAG 1551 (VAG 1552) Scan Tool (ST) and press buttons -0- and -1- to insert "Engine Electronics" address word 01 (engine running at idle). [1][2]Scan Tool Connecting and Initial Checks

Indicated on display


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08, and press -Q- button to confirm input.

Indicated on display


Read Measuring Value Block
Input display group number XXX


- Press buttons -0-, -2- and -4- to input display group number 24, and press -Q- button to confirm input.

Indicated on display


Read Measuring Value Block 24 ->
1 2 3 4


- Check specified values for rear window defogger operating condition (display field 4):
Specified value in display field 4: "R Def OFF"







- Switch rear window defogger on.
Specified value in display field 4: "R Def ON"
- Press -> button to advance program sequence.
- Press buttons -0- and -6- to select "End Output" function 06, and press -Q- button to confirm input.
- Stop engine (switch ignition off).
- Connect VAG 1598/19 test box to ECM harness connector. Connecting VAG 1598/19 Test Box
- Connect VAG 1527 LED voltage tester between ECM/test box sockets C22 and D11 (Ground).
- Switch ignition on.
- Switch rear window defogger on.
LED must light up.

If LED does not light:







- Check for open circuit between ECM/test box socket C22 and rear window defogger switch.
See Electrical Wiring Diagrams, Troubleshooting and Component Locations.