Checking Rear Window Defroster Signal

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.

CHECKING:
- 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).
Indicated on display:

Rapid data transfer HELP
Select function XX

- 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):

Display Group 24:

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.