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Severity: High Code type: Generic (all makes)

U0109 Code: Lost Communication With Fuel Pump Control Module

The PCM lost contact with the module that controls fuel pump speed; stalling or no-start can follow.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 4/5 – High4/5

Severity: High

Meaning
Lost Communication With Fuel Pump Control Module
System
Module Communication · Network
Safe to drive?
With caution
Typical repair cost
$60–$1,600
DIY difficulty
Moderate

Many vehicles no longer run the fuel pump at full speed through a simple relay. A fuel pump control module (FPCM) varies pump speed to hold the fuel pressure the PCM asks for, and on network-based designs it reports back over the CAN bus. U0109 means the PCM, or another module, stopped hearing from it. GM trucks, SUVs and cars use this layout widely, with the module mounted near the tank, under the rear of the body, in the cargo floor or behind a rear trim panel. Mounted low and near the rear wheels, these modules take road water and salt, so connector corrosion and water-damaged housings are the classic causes. Depending on the design, a silent module either stops the pump, causing a stall or no-start, or leaves it at a default speed that can starve the engine under hard acceleration.

How to read U0109

How to read U0109U10213094
  1. U Network
  2. 0 Generic (SAE)
  3. 1 Module Communication
  4. 09 Specific fault

Symptoms

  • Engine cranks but won't start, or stalls and then restarts after a few minutes
  • Hesitation or stumble when accelerating hard or climbing a hill
  • Fuel pump buzzing louder or at a steady pitch, or not priming at key-on
  • Check engine light with low fuel pressure codes
  • Problem worse after driving through water, snow slush or a car wash

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Corroded or water-damaged fuel pump module connector from road splash and salt 28%
  2. Failed fuel pump control module (water intrusion into the housing or internal electronic failure) 24%
  3. Blown fuse, failed relay or corroded ground near the rear of the vehicle 18%
  4. Chafed CAN or supply wiring along the frame rail to the rear 14%
  5. Low battery voltage during cranking 10%
  6. Failing fuel pump drawing excess current and overloading the module 6%

Diagnosis step by step

Diagnostic flow: U01091Scan the pump module and checkpressure data2Locate and inspect the module3Test supply, ignition feed andground4Check the CAN lines at the module5Measure fuel pump current6Replace and configure

  1. Scan the pump module and check pressure data

    Try to connect to the fuel pump module with a scan tool. If it answers, check commanded versus actual fuel pressure and pump duty cycle; if it doesn't, focus on power, ground and bus wiring. Fuel pressure codes alongside U0109 show the engine was actually starved.

    Tools: OBD-II scanner

  2. Locate and inspect the module

    Find the module for your vehicle, typically under the rear of the body, above the spare tire, near the tank or behind a rear panel. Check the housing for cracks and the connector for white or green corrosion and failed seals.

    Tools: Flashlight, Gloves

  3. Test supply, ignition feed and ground

    Back-probe the connector with the key on: battery voltage on the power pin, the ignition or wake-up signal present, and ground drop under about 0.1 V while the pump runs. Rear body grounds corrode badly and often cause intermittent dropouts.

    Tools: Multimeter

  4. Check the CAN lines at the module

    With the key on, CAN-high and CAN-low should sit near 2.6 V and 2.4 V. With the battery off, test continuity to the nearest junction and look for shorts to ground where the harness rides along the frame.

    Tools: Multimeter

  5. Measure fuel pump current

    Before fitting a new module, measure the pump's current draw with an inductive clamp or meter at the module output. A pump pulling well above normal will overheat and kill the new module; replace the pump too if it's worn.

    Tools: Multimeter, Fuel pressure gauge

  6. Replace and configure

    Install the new module with dielectric grease on the seal (not the pins) and program or configure it if the manufacturer requires. Confirm fuel pressure tracks the commanded value during a test drive.

    Tools: OBD-II scanner

Where the parts are

Charging system and control modules – U01091234567
Charging system and control modules
  1. 1Battery
  2. 2Alternator
  3. 3Engine computer (ECM)
  4. 4CAN bus
  5. 5Transmission
  6. 6Wheel speed sensor
  7. 7High-voltage battery

Repair options & costs

RepairDIY?Estimated cost
Clean/repair module connector and ground Yes $60–$300
Repair wiring along the frame No $150–$500
Replace fuel pump control module No $250–$700
Replace module and fuel pump together No $700–$1,600

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Chevrolet

Many Chevrolet trucks, SUVs and cars use a network-connected fuel pump flow control module mounted low at the rear, and corrosion or water damage at that module is a common cause of U0109 with stalling or no-start.

U0109 on Chevrolet in detail

Ford

Ford trucks and SUVs use a fuel pump driver module (FPDM) often bolted to the frame or a crossmember, where dissimilar-metal corrosion eats the housing and connector; on many models those failures set Ford's own FPDM codes instead of U0109.

Field data

Chevrolet 4
Ford 3 Expedition, Focus Bev, Transit

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Depends

If U0109 turns on the check engine light, which is usual when fuel pressure is affected, the vehicle fails a US emissions test. A history code with no light on won't fail by itself.

Frequently asked questions

Can I drive with U0109?

Only carefully and briefly. Depending on the design the pump may stop without warning, so a stall in traffic is a real risk. If it has already stalled once, tow it.

Why does the problem get worse in rain or winter?

The module and its connector sit low at the rear, right in the spray from the tires. Water and road salt get into the connector or housing and cause shorts that come and go with the weather.

Should I replace the fuel pump at the same time?

Only if tests show the pump is drawing too much current or can't hold pressure. A worn pump that overloads the module will destroy a new one, so measure first.

Is this the same as a bad fuel pump relay?

No. On older cars a relay simply switched the pump on. U0109 applies to vehicles with a smart module that controls pump speed and reports on the network, so the tests focus on that module's power, ground and data lines.

Sources