U0105 Code: Lost Communication With Fuel Injector Control Module

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The U0105 diagnostic trouble code (DTC) indicates that the vehicle's PCM/ECM has lost communication with the Fuel Injector Control Module (FICM) through the CAN network. The exact operation and module design may vary depending on the manufacturer and vehicle model.

What Does the U0105 Code Mean?

When the engine control module cannot receive expected messages from the Fuel Injector Control Module, it stores DTC U0105. The problem may be caused by CAN communication faults, power supply issues, wiring problems, connector damage, or a failed FICM module.

On some diesel applications, the FICM controls injector operation by managing injector timing and communication between the engine computer and fuel injection system.

System Overview

The Fuel Injector Control Module communicates with the PCM through the vehicle CAN bus. The PCM sends commands, while the FICM controls injector-related functions and reports operating status back to the PCM.

PCM/ECM
⬇️ CAN High / CAN Low Communication
⬇️
Fuel Injector Control Module (FICM)
⬇️
Fuel Injectors

Symptoms of U0105

  • Check Engine Light illuminated.
  • Engine may crank but not start.
  • Hard starting or intermittent stalling.
  • Reduced engine performance.
  • Fuel injector operation problems.
  • Additional U-series communication codes.

Possible Causes

  • Open or short circuit in CAN communication wiring.
  • Loose or corroded FICM connector.
  • Low battery voltage or charging system problems.
  • Missing power or ground supply to FICM.
  • Blown fuse or faulty relay.
  • Internal FICM failure.

Typical CAN Wiring Check

Battery Power (+)
⬇️
Fuse / Relay
⬇️
FICM Power Input

CAN High (≈2.5V–3.5V)
CAN Low (≈2.5V–1.5V)
⬇️
PCM Communication

Oscilloscope Diagnosis

A healthy CAN waveform normally shows opposite switching between CAN High and CAN Low signals.

  • Normal: CAN High rises while CAN Low drops.
  • Open circuit: Flat or missing communication waveform.
  • Short circuit: Abnormal voltage level with distorted signals.

Live Data Checks

  • Battery voltage: approximately 12.4–12.8V engine off.
  • Charging voltage: approximately 13.5–14.8V engine running.
  • FICM communication status: Connected / Not Available.
  • Network communication errors count.

Diagnostic Procedure

  1. Scan all modules and record all stored U-codes.
  2. Check battery voltage and charging system operation.
  3. Inspect FICM connectors and wiring harness.
  4. Verify FICM power and ground circuits.
  5. Measure CAN High and CAN Low circuits.
  6. Repair wiring or replace/program the module if required.

Can You Drive With U0105?

Severity: Moderate to High. The vehicle may experience poor performance, stalling, or a no-start condition if communication with the Fuel Injector Control Module is lost.

Estimated Repair Cost

  • Fuse or relay replacement: $10–50
  • Connector repair: $30–100
  • CAN wiring repair: $100–400
  • FICM programming: $100–300
  • Fuel Injector Control Module replacement: $400–1,500

Common Repair Mistakes

  • Replacing the FICM before checking power and ground.
  • Ignoring battery voltage problems.
  • Replacing injectors when the actual fault is communication-related.
  • Clearing codes without testing the CAN network.

Recommended Diagnostic Tools

  • Professional OBD-II scanner with module communication access.
  • Digital multimeter for power and ground testing.
  • Oscilloscope for CAN waveform analysis.
  • Wiring diagrams and manufacturer service information.

Related DTC Codes

U0105 may appear with other communication faults such as U0100, U0101, U0073, and U0109.

Frequently Asked Questions

Is U0105 a generic OBD-II code?

U0105 is a standardized network communication code, but the affected module details can vary by manufacturer.

Can a weak battery cause U0105?

Yes. Low voltage can interrupt module communication and create CAN network faults.

Should I replace the FICM immediately?

No. Always test wiring, connectors, power, ground, and CAN communication before replacing the module.

Conclusion

U0105 indicates lost communication with the Fuel Injector Control Module. Accurate diagnosis requires checking the CAN network, electrical supply, connectors, and module operation before replacing expensive components.

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