Code
U1318
PEUGEOT
U — Network/User
Fault absence of communication with the built-in systems interface (BSI): No signal / BSI absent
AI status
Completed
Completed
100%
Causes
- Blown fuse or loss of BSI supply voltage
- Poor or corroded ground(s) to BSI
- Damaged or disconnected CAN/LIN wiring or connectors
- Failed BSI module or internal hardware fault
- Missing or incorrect BSI programming/calibration
- Battery low or recent battery disconnect causing module asleep
Symptoms
- Multiple control modules reporting faults or 'module not present'
- Central locking, lights, or wipers inoperative or intermittent
- Instrument cluster or dash warnings present
- Vehicle may not crank or immobiliser may prevent start
- Faults shown on diagnostic tool for other networks/modules
What to check
- Read and record all DTCs and freeze frame data from all modules
- Check battery voltage (should be ≥12.4V) and charging system
- Inspect fuses and fusible links related to BSI power
- Visually inspect BSI connector(s) for corrosion, bent pins, water ingress
- Check main BSI ground(s) for tightness and continuity to chassis
- Scan for presence of other modules on the CAN bus
Signal parameters
- Battery supply to BSI: ~12–14.5 V with engine off and running respectively
- CAN bus idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each to ground)
- CAN bus dominant: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- CAN differential idle: ≈ 0 V, dominant differential ≈ 2.0 V
- Termination resistance (power off): ~60 ohms across CAN_H–CAN_L (two 120 Ω terminators in parallel)
- BSI ground continuity: low resistance (
Diagnostic algorithm
- Confirm code and note any related U-codes from other modules. Clear DTCs and attempt to re-scan to check for return.
- Verify battery voltage and condition. Recharge battery if low and re-check communication.
- Inspect and test fuses/power feeds to the BSI. Repair any blown fuses and retest.
- Visually inspect BSI connectors and wiring for corrosion, water damage, bent pins or loose terminals. Repair as required.
- Check BSI ground(s) for continuity and tightness. Clean and secure grounding points.
- With ignition on, measure CAN_H and CAN_L at the BSI connector. Compare to expected signal parameters. If bus is silent, check for open circuit to other modules.
- With ignition off/power removed, measure resistance across CAN_H–CAN_L to confirm terminators (~60 Ω).
- Isolate sections: disconnect suspected aftermarket devices, then re-check bus. If other modules present but BSI absent, focus on BSI power/connector or internal failure.
- If wiring and power/grounds are good but BSI does not respond, verify software/calibration version. Reprogram or reinitialise BSI if manufacturer procedure available.
- If reprogramming fails and/or BSI still non-responsive, consider replacement. Ensure correct coding/programming and immobiliser pairing after fitment.
- After repairs, clear stored codes and confirm communication restored and no residual network errors.
Likely causes
- Blown fuse or no battery/ignition power to BSI
- Corroded/loose BSI connector or ground
- CAN bus open/short or missing termination
- BSI hardware fault or software corruption
Fault status
Status
No communication received from the Built-in Systems Interface (BSI) on the vehicle network. BSI is absent or not responding.
Repair difficulty: Hard
Diagnostic time: 1.5 - 4.0 hours
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