Code
U1318
DS
U — Network/User
Fault absence of communication with the built-in systems interface (BSI): No signal / BSI absent
Views:
UK: 1
EN: 0
RU: 0
AI status
Completed
Completed
100%
Causes
- BSI (Built-in Systems Interface) has lost power or ground
- Missing or corroded connector/cable to BSI
- Faulty BSI (internal failure)
- Open/short in CAN bus wiring (CAN High/Low) or poor termination
- Failed CAN transceiver in BSI or another network module
- Blown fuse protecting the BSI or its network
Symptoms
- Multiple systems inoperative (central locking, lights, wipers, etc.)
- Instrument cluster warnings or 'BSI fault' messages
- No response from BSI when scanned with diagnostic tool
- Other modules report network errors or reduced functionality
- Vehicle may not start or start/immobilizer symptoms when BSI is missing
- Intermittent or permanent loss of convenience features
What to check
- Verify battery voltage (stable 12.0–14.5 V) and good battery connections
- Visually inspect BSI connector(s) for corrosion, bent pins, loose terminals
- Check fuses and fusible links related to BSI power and CAN bus
- Use a scan tool to see if BSI appears in module list and whether other modules are communicating
- Check for presence of CAN bus traffic with an OBD-II scan tool or CAN analyzer
- Measure CAN High and CAN Low voltages at the BSI connector with ignition ON
Signal parameters
- CAN bus recessive idle: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (measured relative to chassis)
- CAN bus dominant: CAN_H rises (~3.5 V) and CAN_L falls (~1.5 V) during frames (use oscilloscope to confirm)
- Termination resistance: approx. 60 Ω between CAN_H and CAN_L (two 120 Ω terminators in parallel)
- Bus data: visible CAN frames/traffic when ignition ON using scan tool/CAN sniffer (no traffic indicates absence)
- Supply voltage at BSI: battery voltage present at BSI power pins with ignition in required position
Diagnostic algorithm
- Record symptoms and freeze frame if available. Confirm U1318 stored and note any related U-codes.
- Verify battery voltage and perform basic power/ground checks for the BSI. Replace blown fuses.
- With ignition ON, use a scan tool to request modules. Confirm whether BSI responds or is absent from the network.
- Visually inspect BSI connectors and harness for corrosion, bent pins, or damage. Repair any connector faults.
- Measure voltages at the BSI power and ground pins. Repair power/ground faults before further testing.
- Measure CAN_H and CAN_L voltages at the BSI connector. Check termination resistance (≈60 Ω) with ignition OFF.
- Use a diagnostic tool or oscilloscope/CAN sniffer to look for bus traffic and valid waveform levels. If no traffic, isolate wiring between BSI and nearest module/gateway.
- If a short or open is found, repair wiring and re-test. If wiring is good but no CAN transceiver activity, suspect BSI internal fault.
- Check related modules (gateway, ECU, instrument cluster) for faults that could affect the bus or gateway functionality.
- If BSI suspected faulty after verification of power, ground and bus, consider reflashing/reprogramming or replacing the BSI with correct software/coding. Re-test network communication after replacement.
- Clear codes and road-test to confirm repair. Monitor for reoccurrence and document repairs.
Likely causes
- Blown fuse or BSI not powered (most common)
- Disconnected/corroded BSI connector or poor ground
- CAN bus wiring open, shorted or missing termination
- Failed BSI module or internal CAN transceiver
- Network wiring short to battery or ground after recent repair
Fault status
Status
No communication with BSI detected on the vehicle network. BSI not responding or absent — check power, ground, connectors, CAN wiring and module integrity.
Repair difficulty: Medium
Diagnostic time: 1.5-3.0 hours
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