This post will share a real repair case about fault “Driving stability”. Check following details.
Model: BMW X6
A DSC warning appears in dash, a message displays on CID “Driving stability - Drive control systems malfunction. Reduced driving stability in curves. Drive moderately! Have the system checked by the BMW center.
1. Use INPA scanner to connect car’s OBD port, got two codes: 5224 – VTG: oil wear, 6422 – ICM: interface QMVH
2. “VTG: oil wear” is need to change transfer case oil, but test runs can eliminate faults that are not caused by VTG.
3. “ICM: interface QMVH”, Our preliminary analysis has the following possible causes:
A: QMVH module power supply or ground fault;
B: PT-CAN bus system failure between ICM and QMVH;
C: ICM-CAN bus system failure between ICM and QMVH;
D: Internal fault of QMVH module;
E: ICM module internal failure;
F: Mechanical failure of rear axle lateral torque distribution.
The circuit diagram is as follows:
4. Through computer testing, QMVH communication is normal, and the modules on PT-CAN are communicating well. It can be temporarily judged that there is no problem with the PT-CAN bus. Next, check the ICM-CAN bus between the QMVH module and the ICM module. Checked that the power supply of QMVH is normal, the ground point is normal, and the power supply of measuring ICM is normal.
5. Measured the ICM-CAN waveform as follows, and the preliminary judgment is normal. Compare the PT-CAN and ICM-CAN bus waveforms, they are similar.
6. In order to find the failure point, we can only use the exclusion method to find the failure point. We first disconnected the power and ground wires of the QMVH and the ICM-CAN bus respectively, and found that the fault phenomenon and fault code are different from this time, and then abandoned this idea.
7. Disassembled QMVH module from error car and installed to another same model car, found that the fault was transferred to another car, the cause is QMVH module. After replacing the module, the vehicle is normal, error disappear.
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