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Home / DTC / U0678 — Lost Communication With Fuel Level Sensor C

U0678 — Lost Communication With Fuel Level Sensor C

Detailed page for trouble code U0678.

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U0678

Generic U — Network/User

Lost Communication With Fuel Level Sensor C

Brand: Generic
Type: U — Network/User
Views: UK: 11 EN: 16 RU: 13
AI status
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Page language: EN

Causes

  • Open or short in wiring between fuel level sensor and receiving module
  • Corroded or loose connector at the sensor or ECU/module
  • Failed fuel level sensor or sensor module
  • Failed receiving module (ECU, BCM, IPC) or internal module software fault
  • CAN/LIN bus fault, missing message, or bus off condition
  • Blown fuse or lost sensor power/ground

Symptoms

  • Dash shows incorrect, frozen, or no fuel level reading for tank C
  • Fuel gauge warning lamp or message (e.g., 'Check Fuel Level')
  • Multiple communication-related U codes present
  • Possible fuel range or low-fuel alerts
  • Intermittent or no updates for tank C on scan tool live data

What to check

  • Read and record all stored and pending DTCs and freeze frame data with a capable scan tool
  • Check for other U-codes or network errors (CAN off, bus-off, etc.)
  • Visually inspect connectors and wiring at the sensor, fuel tank, and receiving module(s)
  • Check fuses and power/ground to the sensor module(s)
  • Monitor live data for fuel level C and network messages (CAN/LIN) while key ON/engine running
  • Perform wiggle test on harness to reproduce fault

Signal parameters

  • Typical communication: CAN message (digital) — expect periodic update (commonly 0.5–5 Hz depending on vehicle)
  • Payload: fuel level typically reported as a percentage (0–100) or raw byte(s); message length varies by OEM
  • Analog variants (less common): fuel sender voltage 0–5 V proportional to level
  • Resistive variants (float sender): resistance range depends on vehicle (commonly 0–250 Ω)
  • Expected idle CAN bus voltage: CANH ~2.5–3.5 V, CANL ~1.5–2.5 V; differential ~2.5 V when dominant

Diagnostic algorithm

  1. Verify the code: clear DTCs, then key ON/engine run and attempt to reproduce. Note any immediate reappearance and freeze frame data.
  2. Scan for related U-codes and module status — identify which module expects the fuel level C message.
  3. If the vehicle uses CAN/LIN, use a capable scan tool or scope to monitor the bus for the expected message ID and frequency for fuel level C. If message absent, the fault is upstream.
  4. If message is present but contains invalid data, compare payload to expected format; check for intermittent/noisy communication.
  5. Inspect the sensor connector and wiring at the tank: look for corrosion, bent pins, water intrusion, chafing, or heat damage. Repair as needed.
  6. Verify sensor power and ground at the connector (measure battery voltage on supply pin with key ON). Check fuse/relay feeding the sensor/module.
  7. For analog/resistive senders: measure resistance or voltage at the sensor with key ON and compare to specification or expected range. Move float (if accessible) and observe change.
  8. For CAN/LIN: check bus termination resistance (typ. ~60 ohms for CAN between CANH and CANL with key OFF). Inspect for shorts to battery or ground.
  9. Perform a wiggle test of harness while monitoring live data to find intermittent faults. Use a scope to check for noise on signal lines if needed.
  10. If wiring, power, and ground are good but no valid messages, suspect faulty sensor/module. Replace sensor/module and retest.
  11. After repairs, clear codes, perform functional test and road test to confirm the fault does not return.

Likely causes

  • Disconnected or corroded connector at the fuel level sensor
  • Damaged shielded signal wire or CAN bus conductor between sensor and module
  • Sensor supply voltage absent (fuse, relay, harness break)
  • CAN bus termination missing or shorted causing message loss
  • Sensor module internal failure (common in modules in/near fuel tank)

Fault status

⚠️ Status
Lost Communication With Fuel Level Sensor C
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0121 U0140 U0155 U1000
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