Brake Light Switch: Testing and Inspection

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

Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.

Test requirements







- The Brake Light Switch F fuse OK.







- The Brake Pedal Switch F63 fuse OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, shift selector lever into position "P" or "N".
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Procedure
- Remove the drivers side storage compartment.

Checking internal resistance
- Disconnect the Brake Light Switch F / Brake Pedal Switch F47 Electrical harness connector.







- Using a Multimeter, check the Brake Pedal Switch F47 terminals 1 to 4 for a internal short.

Specified value: infinity.

If the specified value was not obtained:
- Replace the Brake Light Switch F / Brake Pedal Switch F47.

If the specified value was obtained:







- Using a Multimeter, check the Brake Pedal Switch F47 terminals 1 to 4 for resistance.
- Depress the brake pedal.

Specified value: approx. 0 Ohm

If the specified value was obtained:
- Check the voltage supply of the Brake Light Switch F / Brake Pedal Switch F47.

If the specified value was not obtained:
- Replace the Brake Light Switch F / Brake Pedal Switch F47.

Checking voltage supply
- Switch the ignition on.







- Using a Multimeter, check the Brake Pedal Switch F47 electrical harness connector terminal 4 to Ground (GND).

Specified value: battery voltage.

If the specified value was not obtained:
- Using a Multimeter, check the Brake Pedal Switch F47 electrical harness connector terminal 2 to Ground (GND).
- Switch the ignition off.

Specified value: battery voltage.

If the specified value was not obtained:
- Check the wiring.

If the specified value was obtained:
- Replace the Brake Light Switch F / Brake Pedal Switch F47.

Checking wiring
If the manufacturers test box is being used. Perform the following step.
- Install the test box.

If the manufacturers test box is not being used. Perform the following step.
- Remove the Motronic Engine Control Module (ECM) J623.







- Using a Multimeter, check the Brake Light Switch F / Brake Pedal Switch F47 electrical harness connector to the Motronic Engine Control Module (ECM) J623 electrical harness connector T94 for open an circuit.

Brake Light Switch F / Brake Motronic Engine Control Module
Pedal Switch F47 electrical (ECM) J623 electrical connector
harness connector terminals T94 terminals or test box sockets
1 47
3 25

Specified value: 1.5 Ohms Max.

If the specified value was not obtained:
- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).
- Check the wiring connection for damage, corrosion, lose or broken terminals.
- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring and voltage supply was not OK:
- Replace the Motronic Engine Control Module (ECM) J623.
- Install the drivers side storage compartment.

Final procedures
After the repair work, the following work steps must be performed in the following sequence:
1. Check the DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If the DTC memory was erased, generate readiness code.

- End of diagnosis.