PSM, Function of Individual Components

Function Of Individual Components

PSM 5.3/PSM 5.7

Information and warning lights







The driver is informed of the PSM control activities by means of the display lights in the instrument cluster. The display lights illuminate for a lamp check when the ignition is switched on. The information and warning lights are triggered via the CAN bus as of model year 2002.
1 - Information light for FDR, ASR and ABD. If FDR, ASR or ABD is function, the light flashes.
2 - PSM warning light. The warning light illuminates if: FDR is faulty, ABS is faulty, FDR is switched off via the rocker switch or the ABD is in function.
3 - ABS warning light. The warning light illuminates if the ABS is faulty.

Lateral acceleration sensor PSM 5.3







The lateral acceleration sensor is installed on the centre console in longitudinal direction.

The transverse acceleration sensor supplies information about the transverse accelerations occurring in the vehicle to the PSM control module. Together with the information from the steering-angle sensor and the rate-of-turn sensor, the current handling behaviour with respect to its transverse dynamics is calculated. The sensor element is a damped spring-and-mass system. Its deflection is detected magnetically using a linear Hall element. The deflection is a direct measure of the occurring transverse accelerations.

Lateral acceleration sensor PSM 5.7







The transverse acceleration sensor and the rate-of-turn sensor are combined in one housing in the PSM 5.7. The components are fitted on a printed circuit board and operate according to the micro- mechanic principle. The sensor is connected via a six-pole plug. The transverse acceleration is measured according to a capacitive principle. Without the transverse acceleration measurement, it is impossible for the PSM control module to calculate the actual vehicle condition. The PSM function is switched off.

Rate-of-turn sensor PSM 5.3







The rate-of-turn sensor is located underneath the seat on the right in the PSM 5.3.

The rate-of-turn sensor supplies the PSM control module with an analog voltage signal which corresponds to the yaw speed of the vehicle.

Rate-of-turn sensor PSM 5.7







The rate-of-turn sensor is combined with the transverse acceleration sensor in the PSM 5.7 and is installed on the centre console in longitudinal direction.

The rate of turn is recorded by measuring the occurring Coriolis acceleration. Together with the information from the steering-angle sensor and the rate-of-turn sensor, the current handling behaviour with respect to its transverse dynamics is calculated. Without measurement of the yaw speed, it is not possible for the PSM control module to detect whether the vehicle is developing a tendency for spinning. The PSM function is switched off.

DME Tiptronic control module

DME control module
The DME control module is connected to the PSM control module by means of a CAN bus. Among others, the following signals are sent via this data lead:
- engine speed
- engine torque
- acceleration pedal position.

Tiptronic control module
The Tiptronic control module is also connected to the PSM control module by means of the CAN bus. The Tiptronic control module receives commands through the CAN bus to execute or not to execute shift operations as necessary.

Control module PSM 5.3







The control module in the PSM 5.3 is installed at the front left of the luggage compartment. The installation position ensures that the control module plug can be pulled off only after the control module has been removed. The plug is designed so that the warning lights are activated if the connection is incorrect (short circuit bridge). The control module is located directly on the hydraulic unit.

Brake system
The brake master cylinder, the vacuum brake booster, the hydraulic unit and the booster pump are installed in the front end. The brake master cylinder is a tandem brake master cylinder with modified central valve.

Brake system PSM 5.3







1 - Expansion tank
2 - Vacuum booster
3 - Brake master cylinder
4 - Booster pump with brake pressure sensor
5 - Hydraulic unit

Brake system PSM 5.7







1 - Expansion tank with brake fluid level switch
2 - Vacuum booster
3 - Brake master cylinder
4 - Booster pump (on the right side of the front end in the Carrera 2)
5 - Hydraulic unit with control module and brake pressure sensor

Booster pump PSM 5.3/PSM 5.7
A sufficiently fast pressure increase in the wheel brakes is important for perfect control of the driving dynamics. In order to guarantee a secure flow capacity of the return pump across the entire temperature range, the booster pump is switched in the case of driving dynamics control and an admission pressure of up to 20 bar is built up in front of the return pumps.

Booster pump Carrera 2







The booster pump is located on the opposite side of the hydraulic unit in the Carrera 2.

Booster pump Carrera 4







The booster pump is located next to the hydraulic unit in the Carrera 4.

Brake pressure Sensor
The brake pressure sensor records the brake pressure (desired deceleration), which is used by the PSM control module to calculate the wheel brake forces (longitudinal forces). If driving dynamics control is necessary during the braking procedure, the existing wheel brake forces are included to calculate the lateral traction.

Brake pressure sensor PSM 5.3







The brake pressure sensor is located on the booster pump on the PSM 5.3.

Brake pressure sensor PSM 5.7







The brake pressure sensor is on the hydraulic unit on the PSM 5.7.

Stop light switch
When the brake is actuated, signals from the twin contact (make and break) are detected and evaluated by the control module. If the brake is actuated during an ASR control operation, this procedure is immediately interrupted in order to initiate an ABS control operation. During an FDR control operation, these signals are processed in addition to the brake pressure signal.

Steering-angle sensor







The steering-angle sensor supplies information about the slip angle of the front wheels to the PSM control module (intention of driver in relation to direction of travel). In the PSM control module this signal is used to calculate the required vehicle behaviour with respect to its transverse dynamics by means of the calculation of the vehicle speed. The sensor has its own microcontroller. The information is transmitted to the PSM control module by means of a CAN bus. With- out the information from the steering-angle sensor, the PSM control module cannot produce a picture of the desired direction of travel. If the steering angle sensor is replaced, a calibration must be performed.

PSM OFF switch







The system can be switched off by means of a switch in the centre console. System deactivation is displayed by the indicator light in the PSM switch and in the instrument cluster. The ABD function (automatic brake differential) is maintained when the PSM is switched off. For safety reasons, the driving dynamics control is reactivated temporarily for the duration of one brake pedal actuation.

Switch for parking brake control
When the parking brake is engaged, the parking brake contact closes and sends a ground signal to the PSM control module. In order to avoid an excessive increase of the torque on the drive wheels, engine drag torque control operation is not permitted if a signal is present.

Speed sensors
The wheel speed sensors supply the PSM control module with information about the current wheel speed.



Component Arrangement

PSM 5.3/911 Carrera 4 (996) -> Mod. 1999







PSM 5.7/911 Carrera 4 (996) 2/4 Mod. 2000 ->

Part 1:

Part 2: