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Home / DTC / U1118 — Fault absence of communication with the built-in systems interface (BSI): No signal

U1118 — Fault absence of communication with the built-in systems interface (BSI): No signal

Detailed page for trouble code U1118.

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U1118

DS U — Network/User

Fault absence of communication with the built-in systems interface (BSI): No signal

Brand: DS
Type: U — Network/User
Views: UK: 3 EN: 6 RU: 7
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Page language: EN

Causes

  • BSI has no power (fuse, relay, battery supply, internal failure)
  • Damaged or disconnected BSI connector or wiring harness
  • CAN bus fault: open, short to ground/Vbatt or missing termination
  • Corroded or water-damaged BSI or connectors
  • Module asleep or not woken (low battery/voltage)
  • Software/firmware mismatch or corrupted BSI software

Symptoms

  • Multiple body systems inoperative or behaving intermittently (lighting, wipers, central locking)
  • No response from BSI-controlled functions (e.g., keyless entry, interior lighting)
  • Instrument cluster warnings or multiple communication fault lamps
  • Unable to read BSI on diagnostic tool / module not present in network scans
  • Occasional no-start or immobilizer-related symptoms if BSI handles security

What to check

  • Confirm vehicle battery voltage and health; charge or connect stable supply if low
  • Scan full network with a compatible diagnostic tool to list present modules and related U-codes
  • Check fuses and relays related to BSI power and accessories
  • Visually inspect BSI connector(s) and nearby wiring for corrosion, water, pin damage or loose pins
  • Measure CAN bus voltages at the BSI connector (CANH/CANL) and check for correct idle voltages and differential
  • Measure termination resistance across CANH and CANL (approx. 60 Ω with ignition off/wake state as appropriate)

Signal parameters

  • Vehicle battery nominal: ~12.0–12.6 V (engine off); 13.5–14.8 V (engine running)
  • CAN bus idle voltages (nominal): CANH ≈ 2.5 V, CANL ≈ 2.5 V (with small common-mode idling); dominant state typically ~3.5 V (CANH) / ~1.5 V (CANL)
  • CAN differential idle: ~0 V (no dominant) and dominant differential ≈ 2.0 V
  • Termination resistance: ~60 Ω measured between CANH and CANL (two 120 Ω in parallel)
  • BSI supply pin: battery feed voltage present at appropriate connector pin when ignition on

Diagnostic algorithm

  1. Verify battery voltage and health; ensure stable supply before testing network modules.
  2. Use a dealer/OEM-capable scan tool to check network topology and verify whether the BSI is detected. Note any additional U-codes.
  3. Check and replace any blown fuses or faulty relays that feed the BSI. Inspect fusebox for corrosion.
  4. Perform visual inspection of BSI connector and harness for moisture, corrosion, bent pins or rodent damage; repair and reseal as required.
  5. Measure power and ground at the BSI connector (VBATT, ignition-switched supply, ground). If power missing, trace and repair supply circuit.
  6. With ignition in wake/key on (per manufacturer procedure), measure CANH and CANL at the BSI connector: verify idle and dominant voltages and differential. Compare to expected values.
  7. Measure termination resistance across CANH and CANL. If out of range, isolate modules and re-measure to find short/open module.
  8. If a short to battery or ground is suspected, isolate branches of the CAN network and use backprobing/continuity tests to find the fault.
  9. If wiring and power are good but BSI not present on network, attempt a BSI wake-up/reset per manufacturer procedure. Reflash or update BSI software if available and recommended.
  10. If all electrical checks pass and software update does not restore communication, consider replacing the BSI or performing module bench testing/repair. Verify correct part coding/programming after replacement.
  11. After repairs, clear codes and perform a full network scan and functional checks to confirm restoration of communication.

Likely causes

  • Blown/loose fuse or removed battery leading to BSI unpowered
  • Broken/loose BSI connector or wiring near BSI (common failure point)
  • CAN bus short (CANH to Vbatt or CANL to ground) or missing 60 Ω termination
  • BSI internal failure or water ingress causing module to be dead
  • Vehicle in a sleep/secure mode preventing BSI wake-up

Fault status

⚠️ Status
U1118 — Absence of communication with Built-in Systems Interface (BSI): diagnostic tool or other modules receive no signal from the BSI on the vehicle network. Indicates BSI not present or not responding on the CAN bus.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours

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