364 Stop Light Switch - Signal Implausible

P1574

364 Stop Light Switch - Signal Implausible

Function
The signal from the stop light switch is basically used to deactivate the cruise control. For safety reasons, two switches (in one housing) are installed. The actuation of the brake indicates that the driver wishes to interrupt the control loop of the cruise control. It is therefore important that brake actuation is reliably recognized.

Stop light switch 1 opens when the brake is pressed.
Stop light switch 2 closes when the brake is pressed.

Further, in systems with an electrical accelerator pedal, the stop light switch also ensures emergency driving operation if one of the pedal sensors should fail.

Diagnosis conditions
- Ignition on

P1574:

Wiring Diagram







Diagnosis Procedure







1 Check stop light switch.
1. Remove stop light switch.
2. Connect ohmmeter to pins 1 and 4.

Display: 0 - 5 ohms

3. Actuate stop light switch.

Display: infinity ohms

4. Connect ohmmeter to pins 1 and 2.

Display: infinity ohms

5. Actuate stop light switch.

Display: 0 - 5 ohms

6. Install stop light switch.

2 Check wiring from DME control module to stop light switch 1 for short circuit to B+.
1. Connect special tool 9637.
2. Connect voltmeter to pin IV/24 and ground.
3. Switch on the ignition.

Display: 0 V

4. Actuate brake.

Display: battery voltage

If battery voltage is displayed for point 3, check wiring harness for chafing and pinching damage.

3 Check wiring from DME control module to stop light switch 2 for short circuit to B+.
1. Connect special tool 9637.
2. Connect voltmeter to pin IV/28 and ground.
3. Switch on the ignition. Display: battery voltage
4. Actuate brake.

Display: 0 V

If battery voltage is displayed for point 4, check wiring harness for chafing and pinching damage.