Brake Light Switch: Testing and Inspection

Brake Light Switch, Checking

Recommended special tools and equipment
- V.A.G1526 multimeter or V.A.G1715 multimeter
- V.A.G1594 connector test kit
- Wiring diagram

Test requirements







- Corresponding fuses on fuse holder in instrument panel, left side, for Brake Light Switch -F- must be OK.

NOTE: Fuses on this fuse holder are labelled "SC" in the wiring diagram.

- Motronic Engine Control Module (ECM) Power Supply Relay -J271- (relay position R4) must be OK, check.
- Battery voltage must be at least 11.5 Volts.
- All electrical consumers such as, lights and rear window defroster must be switched off.
- Ground (GND) connections between engine and chassis must be OK.
- Ignition switched off.

Test sequence
Observe safety precautions.
Observe rules for cleanliness.

- Remove driver's side storage compartment







- Disconnect 4-pin connector -arrow- from Brake Light Switch -F-


Checking voltage supply







- Connect multimeter using adapter cables to terminal 4 of connector and chassis Ground (GND) for voltage measurement.
- Switch ignition on.

Specified value: at least 11.5V

- Switch ignition off.

If there is a malfunction in voltage supply:
- Check wire between 4-pin connector terminal 4 and corresponding fuse holder for open circuit according to wiring diagram.

Wire resistance: max. 3.0 Ohms

- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If there is no malfunction in voltage supply:
- Check wires to Engine Control Module (ECM) according to wiring diagram.

Checking wires to Engine Control Module (ECM)
- Connect test box to 94-pin connector of wiring harness. Test Box, Connecting For Wiring Test

Engine Control Module (ECM) is not connected.







- Check wires between test box and 4-pin connector to Engine Control Module (ECM) for open circuit according to wiring diagram.

Terminal 2 + socket 1
Terminal 3 + socket 25

Wire resistance: max. 3.0 Ohms

- Check wires for short circuit to each other.

Specified value: Infinity Ohms

- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

If no malfunctions are found in wires:
- Replace Brake Light Switch -F-.
- Install brake light switch.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

Installing brake light switch

NOTE:
- After removing, brake light switch must always be replaced.
- Pedals must not be operated during installation.
- While guiding in, plunger of brake light switch adjusts itself automatically.







- Pull out plunger -arrow- completely from switch.
- Guide retaining tabs -1- and -2- into recesses of mounting bracket.
- Engage brake light switch in mounting bracket by a rotation of about 45 degrees clockwise.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes