Brake Light Switch: Testing and Inspection

Signal From Brake Light Switch F / Brake Pedal Switch F47, Checking

Special tools, testers and auxiliary items required
- Hand multimeter V.A.G 1526 or Multimeter V.A.G 1715
- Connector test set V.A.G 1594
- Wiring diagram

Test conditions:







- The respective fuse (SC 14) of Brake Light Switch F must be OK.







- The respective fuse (SB 7) of Brake Pedal Switch F47 must be OK.
- Battery voltage must be at least 11.5 Volts.
- All electrical consumers (e.g. lights and rear window defroster) must be switched off.
- The parking brake must be applied, otherwise daytime running lights are switched on.
- If vehicle is equipped with an A/C system, it must be switched off.
- The Ground (GND) connections between engine and body must be OK.
- Ignition switched off.

Function test:
- Connect Vehicle Diagnostic and Service Information System VAS 5052.
- Press button "Self-Diagnosis" on tester display.







- Press button "01 - Engine electrical" on tester display.







- In selection - 1 -, click on diagnostic function "08 - Read measuring value block".







- In button field - 2 -, select display group "066" and confirm input by pressing Q button.







- Observe indicated value in display field 2.

1. Read measuring value block"
2. Display fields 1 through 4 below one another
3. Display group X
Specification: XXXXXX00

- Depress brake pedal and hold brake pedal depressed.

Specification: XXXXXX11

- End diagnosis and switch ignition off.

If specification is not obtained:
- Check voltage supply of Brake Light Switch F / Brake Pedal Switch F47 and wiring to Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) J248.

Checking voltage supply:
- Remove cover in driver side footwell
- Disconnect 4-pin connector to Brake Light Switch F / Brake Pedal Switch F47.







- Connect Multimeter V.A.G 1526 to terminal 1 and Ground (GND) for voltage measurement, using jumper wires from connector test set V.A.G 1594.
Specification: approx. battery voltage
- Switch ignition on.
- Connect Multimeter V.A.G 1526 to terminal 2 and Ground (GND) for voltage measurement, using jumper wires from connector test set V.A.G 1594.
Specification: approx. battery voltage
- Switch off ignition.

If specifications are not obtained:
- Check wiring.

If specified values are achieved:







- Connect Multimeter V.A.G 1526 to terminals 1 and 4 for resistance measurement, using jumper wires from connector test set V.A.G 1594.
Specification: Infinite Ohms
- Operate brake pedal.
Specification: approx. 0 Ohms
- Connect Multimeter V.A.G 1526 to terminals 2 and 3 for resistance measurement, using jumper wires from connector test set V.A.G 1594
Specification: approx. 0 Ohms
- Operate the brake pedal.
Specification: Infinite Ohms

If specified values are achieved:
- Check wiring

If specifications are not obtained:
- Replace Brake Light Switch F / Brake Pedal Switch F47

Checking wiring:
- Connect test box to Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) J248 wiring harness.
- Connect adapter cable V.A.G 1598/39-2 to test box V.A.G 1598/42.







- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.

Contact Test box socket
3 65
4 87

Wiring resistance: max. 1.5 Ohms

- Check wires for short circuit to each other, to B+ and Ground (GND).
Specification: Infinite Ohms

If no malfunction is detected in wiring:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) J248