Code
U1318
CITROEN
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 no power to the BSI
- Battery low or poor battery connection
- Disconnected, corroded or damaged BSI connector or wiring harness
- Open, shorted or improperly terminated CAN/LIN bus
- Faulty BSI/module internal failure
- Aftermarket device or recent repair that disturbed network wiring
Symptoms
- Multiple body functions inoperative or intermittent (lights, wipers, central locking)
- Instrument cluster warnings about BSI or network faults
- Key/immobiliser or remote central locking malfunction
- Loss of communication errors on diagnostic tool for BSI and other modules
- Inability to program or communicate with car via diagnostic socket
What to check
- Verify battery voltage at rest and while cranking (should be ~12.4–12.8V at rest, >11V while cranking)
- Check fuses related to BSI (constant power and ignition-switched power)
- Visually inspect BSI connectors and wiring for corrosion, damage or water ingress
- Check for CAN bus activity with a scan tool or oscilloscope
- Measure CAN termination resistance across CAN_H and CAN_L (~60 ohms total)
- Scan for other U-codes or BSI-specific fault entries
Signal parameters
- Battery supply to BSI (Terminal 30): ~12.0–14.4 V (when engine running)
- Ignition-switched supply (Terminal 15): ~12.0 V with ignition ON, 0 V off
- Ground: 0 Ω continuity to chassis ground
- CAN bus idle voltages (recessive): ~2.5 V on CAN_H and CAN_L (both around mid-rail)
- CAN bus dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2 V)
- CAN bus termination: ~60 ohms between CAN_H and CAN_L (two 120Ω in parallel)
Diagnostic algorithm
- Read and record all stored faults with a capable diagnostic tool and note freeze-frame or related codes.
- Attempt to communicate with BSI using scan tool. Confirm complete absence of responses (not just occasional frame errors).
- Check vehicle battery state and connections. Recharge or replace battery if low, then re-test communication.
- Inspect and verify fuses for BSI power circuits (constant 12V and switched 12V). Replace any blown fuses and retest.
- Visually inspect BSI connector(s) for corrosion, bent pins, water ingress or mechanical damage; secure and reseat connectors.
- Measure power and ground at the BSI connector pins: verify terminal 30 and terminal 15 voltages and a good ground.
- Verify CAN bus integrity: measure termination resistance (~60 Ω), check for short to ground or battery on CAN_H/CAN_L, and confirm bus activity with a scope or scan-tool live data.
- Disconnect aftermarket modules or accessories that interface with the body network and retest to rule out external interference.
- If wiring and power/ground are good but no communication, consider reprogramming or software update if available; consult manufacturer service information.
- If all checks pass and communication is still absent, consider replacing the BSI only after verifying root-cause (replace wiring/connector repairs first). After replacement, program/configure the new module per manufacturer procedures.
- Clear codes and verify restoration of communication and normal operation; monitor for recurrence.
Likely causes
- Faulty or blown BSI power fuse (permanent 12V or switched 12V)
- Damaged CAN bus wiring (short to ground/power or open)
- Corroded connector pins at BSI or junctions
- Failed BSI module
- Vehicle battery voltage below minimum required for module operation
Fault status
Status
No signal / BSI absent — diagnostic tool cannot detect the Built-in Systems Interface on the vehicle communication bus.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email