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U0109 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

U0109 is an OBD-II Code that refers to Lost Communication with Fuel Pump Control Module (FPCM)

Meaning

A U0109 code is a diagnostic trouble code that occurs when the other control modules on the vehicle are not communicating with each other. The most common method of communication between components is called Controller Area Network bus communications, or simply CAN bus. Without this CAN bus, control modules won’t be able to communicate with one another, and your scan tool may not be capable of obtaining information from the car, depending on which circuit is disrupted.

Causes

Common causes for this code include:

  • Wiring and/or connectors that are damaged, burnt, shorted, disconnected, or corroded
  • Circuit Open in the CAN bus (+ or -)
  • Circuit short to power in either CAN bus 
  • Circuit short to ground in either CAN bus 
  • Faulty control module (Rare)

Symptoms

The symptoms of a U0109 code are:

  • Illuminated Check Engine Light 
  • Vehicle will crank but not run 
  • If the engine turns on: Outside of these, though, there are other signs to look for. Look for hesitation; a lack of power; poor functioning products and equipment; misfiring cylinders (running rough).

Diagnosis

To diagnose a U0109 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Visually inspect all wiring and connectors in the CAN bus
  3. Repair or replace all damaged, shorted, burnt, disconnected or corroded wires or connectors 
  4. Check for proper CAN bus voltage with a multimeter. If this checks out okay, check resistance of both buses with a multimeter to look for an open circuit
  5. If all else fails, replace the control module

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a U0109 code:

  • Not thoroughly inspecting all the wiring and connectors.
  • Not checking the proper voltage or resistance on the CAN bus.
  • Not replacing all damaged, shorted, burnt, disconnected or corroded wires or connectors.
  • Replacing the wrong part or assuming the problem is with a control module when it’s actually a wiring or connector issue.

How serious is this?

A U0109 code is a serious code that can prevent your vehicle from starting or running. If the problem is not resolved, it could result in a complete loss of communication between control modules on your vehicle. This could mean that your engine will not start, or that certain functions and features of your car may not work properly.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Repair or replace any faulty parts such as wiring, connectors, or control modules.
  • Check all the wiring and connectors for damage, shorting, or other problems. 
  • Resolve any open circuits in the CAN bus.
  • Replace any corroded or burnt wiring or connectors.

Related codes

A U0109 is related to and may be accompanied by the following codes:

P0605 – FPCM Circuit Malfunction

U0121 – Lost Communication with ECM

P1514 – Fuel Pump Relay Control Circuit Malfunction

P0677 – Fuel Pump Voltage Out of Range

Conclusion

In conclusion, the U0109 code is a diagnostic trouble code that refers to a problem with the communication between control modules on your vehicle. This can be caused by a number of different issues, such as faulty wiring or connectors, an open circuit in the CAN bus, or a short circuit to power or ground. If you are experiencing this code, it is important to have it diagnosed and repaired as soon as possible.