CASE 007
Multiple Modules Offline (CAN Failure)
advanced
25 min
Diesel
Vehicle
- ModelTraining SUV 2.0
- Engine2.0 CRDi
- Mileage121,000 km
Customer complaint
The instrument cluster shows several warnings. The engine runs but the ABS, stability and airbag lights are all on. The scanner cannot reach several modules.
History
The customer recently had a windscreen replaced.
Fault codes
U0100 Lost communication with ECM/PCMU0121 Lost communication with ABSU0151 Lost communication with airbag
Live data
- Modules respondingOnly engine management responds
Measurements
- CAN-H to CAN-L resistance, ignition offAbout 120 Ω
- CAN-H voltage, bus activeStatic, no activity
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Diagnostic case
Next step — Reasoning.
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Confirmed cause
Open circuit in the CAN bus (likely harness damage near the recently worked area), leaving one terminator and no activity.
Reasoning
Multiple unrelated modules offline at once points to the shared network, not the modules. Resistance of about 120 Ω instead of around 60 Ω and a silent bus indicate an open bus. Work done recently is a prime suspect for harness damage.
Recommended repair
- Inspect and repair the CAN harness, especially near recent work.
- Re-measure resistance and scope bus activity.
- Clear codes and confirm all modules communicate.
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.