Lateral Acceleration Sensor
Notes On Checking
Checking relates to the following aspects:
- correct installation position of the sensor
- sensor function
The 55-pin ABS 2 LED adapter lead, a multimeter, a shop trolley jack and a measuring tape are required for this test. The 55-pin adapter lead required to run an ABS test on the Carrera 4 (964) and the 928 with PSD (instead of the 35-pin adapter lead) has 3 outputs incorporated for testing the longitudinal and lateral acceleration sensors. The longitudinal acceleration sensor is only fitted to the Carrera 4 (964).
1. With the ignition switched off, take off the ABS/PSD control unit connector and connect it to the 55-pin ABS 2 LED adapter lead.
Note
The following tests can be carried out with or without the ABS 2 LED tester being connected. The 3 outputs are identified by special symbols.
A = Signal of longitudinal acceleration sensor.
B = Signal of lateral acceleration sensor.
C = Ground contact for both sensors.
2. With the vehicle in normal position, check and record the voltage reading at the lateral acceleration sensor (with the ignition switched on).
Specification: 2.7 ± 0.14 volts.
Normal position means: Vehicle must be on a level surface. If the vehicle was off the ground before the test, slacken the suspension if required (move vehicle a few yards and jounce front and rear ends of vehicle several times).
If the reading deviates from the specification, continue with the assessment table at the end.
3. Establish a ground clearance of approx. 150 mm at the left front wheel by lifting the vehicle at the left front jacking point. Read off and record sensor voltage value.
4 Lower left front side of vehicle. Then raise vehicle at the front right end in the same manner by approx. 150 mm. Read off and record sensor voltage value.
5. Assess readings according to the below table. Correct any faults that may be present.
Sensor installation position via output voltage.
The sensor is supplied with an input voltage of 5 volts across the ABS /PSD control unit. The output voltage is 2.7 volts, provided that the sensor is in a horizontal position and fully operative.
- Specified reading: 2.7 ± 0.14 volts when the vehicle is on a level surface (ignition is switched on).
If the reading exceeds or falls below the specification, this means that the sensor bracket is bent or that the sensor is faulty.
If no voltage is displayed, the wiring has gone open circuit, the sensor is faulty or an incorrect socket was used at the test lead. Check wiring routing according to wiring diagram if required. Some faults (open circuit / short circuit, sensor fault) are stored in the fault memory of the ABS/PSD control unit.
The fault memory (in PSD system) must therefore be read out with System Tester 9288 and erased after the fault has been eliminated.
Sensor operation
To test, raise vehicle once at front right and once at front left by approx. 150 mm in each case.
This must result in an exactly predefined change of the voltage.
Use the above measurement (initial reading obtained with vehicle on level surface) as a reference.
- Specified display: Based on the initial reading, the voltage must be higher when the left side is raised and lower when the right side is raised.
Example:
Initial reading 2.65v
Raised at front left 2.85v
Raised at front right 2.46v
If the voltage does not change when the vehicle is raised (by the same amount on left and right), this means that the sensor is faulty.
Read out fault memory (in PSD system) with System Tester 9288 after eliminating the fault and erase the fault memory as required.