928 Psd Off Warning

Fault overview/Troubleshooting (diagnosis/test plan)

Test point DTC Fault display (short fault text) Page

1 11 Transverse lock valve D39 - 230

2 12 Lateral acceleration sensor, D39 - 232

short circuit/discontinuity

3 13 Lateral acceleration sensor, D39 - 233

signal implausible

4 14 Transverse lock, deviation D39 - 234

5 15 Control unit defective D39 - 235

6 21 Speed sensor, front left D39 - 236

7 22 Speed sensor, front right D39 - 238

8 23 Speed sensor, rear right D39 - 238

9 24 Speed sensor, rear left D39 - 238

10 31 ABS valve, front left D39 - 238

11 32 ABS valve, front right D39 - 240

12 33 ABS valve, rear axle D39 - 240

13 34 Valve relay D39 - 241

14 35 Return pump D39 - 245

DTC memory / Troubleshooting Important notes

If warning displays light up and/or faults are shown in the DTC memory of the PSD/ABS, they may also have been triggered by the following problems:

— Control unit supply voltage less than 9.5 Volt (undervoltage)

— Control unit plug disconnected.

— Contact resistance caused by poor ground connections, leading to differences in potential or inadequate shielding of speed sensors. The poor ground connection may not only occur at the affected components, but also at other important grounding points.

— lmportant:The warning "PSD off' may appear in the display fields of the instrument cluster, even though no fault is stored in the DTC memory. Check the lock hydraulics (lock operation) in this case (as of Page D39-247).

Combined plug connections - distinguishing between wires

In the brake pad wear, speed sensor and HF sending unit wiring there are several combined plug connections of similar pattern. In this area, the wires can be distinguished as follows:

— Shielded wires for the speed sensors and HF sending units.

— 2 wires with a protective tube for brake pad wear.

— One pin and one socket exist on the HF sending unit plug connections. The speed sensor plug connections possess 2 pins as well as 2 sockets on the opposite side.

— Two combination connectors are located one above the other in the spare tire area. The wires are identified there with L = rear left and R = rear right.

Troubleshooting aids

When measuring with the multimeter at the control-unit plug, make up 1 or 2 auxiliary leads in your own workshop, each with 2 flat pin plugs No. 17.457.2, to avoid damaging the plug contacts in the control-unit plug during the test.

Replacing the hydraulic unit

After installing/bleeding the ABS hydraulic unit, carry out a complete ABS test with the ABS 2-LED tester.

Test-drive after eliminating the fault.

Clear the DTC memory after eliminating the fault. Perform a test drive and then read out the DTC memory again, if necessary (e.g. in the case of a fault in the speed sensors), also clear the DTC memory of the RDK control unit.

Fault, DTC

Possible causes, remedy, notes

Test point 1

Transverse lock valve DTC 11

No feedback signal from valve to control unit.

1. Switch off the ignition. Pull the plug off the control unit. Check that circuits at plug are not interrupted.

PIN 21 to PIN 23 PIN 21 to PIN 17

If necessary, interrupt the wiring path (plug on transverse lock solenoid valve) and localize the discontinuity by reference to the wiring diagram.

2. Pull off valve relay (No. 1) on the hydraulic unit. (Remove wheel housing cover at the front-left side).

Check for a short circuit to plus or ground in the wiring path, as described in point 1, by measuring at PIN 21. If there is a fault in the wiring path, separate it as described in point 1 so that the unwanted connection to the positive or negative side can be located.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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