U0109 on 2007-2012 Chevrolet Avalanche: Lost Communication With Fuel Pump Control Module Fixes

What's Unique About the 2007-2012 Chevrolet AVALANCHE

On this generation of GM trucks (GMT900 platform), including the Avalanche, the Fuel Pump Control Module is notoriously mounted on a frame cross-member above the spare tire. This location exposes it directly to road salt, water, and debris kicked up by the tires. The module's aluminum backplate and the connector pins are highly susceptible to galvanic corrosion, causing the module to fail internally or lose its connection. This poor design choice is the primary reason U0109 is a common code on these vehicles.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Engine cranks but will not start.
• Engine stalls unexpectedly.
• Reduced engine power or 'limp mode'.
• Check Engine Light is on.
• Transmission may not shift correctly (often accompanied by other U-codes).
• Other warning lights on the instrument panel may illuminate.
• No audible 'hum' or 'whine' from the fuel pump when the key is turned to the 'ON' position.

Most Likely Causes

1. Failed Fuel Pump Control Module (FPCM) 🔴 High Probability → Shop Fuel Pump The module is mounted under the truck on the frame rail, where it is exposed to moisture and road salt, leading to internal corrosion and failure of the electronics and the aluminum housing.
   How to confirm: After verifying power, ground, and communication wires to the module are intact, the module itself is the most likely point of failure. A bi-directional scan tool can attempt to communicate directly with the FPCM; a lack of response points to a bad module. Visually, the module may appear swollen or have a corroded, chalky white backplate.
   Typical fix: Replace the Fuel Pump Control Module. Many aftermarket modules (like Dorman) come pre-programmed and are plug-and-play. An OEM ACDelco module will require programming to the vehicle's VIN by a dealer or a properly equipped shop. Some owners choose to mount the new module in a more protected location or apply a protective coating.
   Est. part cost: $70-$150
2. Corroded or Damaged Wiring/Connector 🟡 Medium Probability The FPCM connector and nearby wiring are in a vulnerable location under the vehicle. The underhood fuse block is also known to suffer from water intrusion, causing corrosion on fuse terminals that power the FPCM circuit (Fuse #21 is a common culprit).
   How to confirm: Visually inspect the FPCM connector for green or white corrosion and damaged pins. Check the FPCM fuse (often labeled 'FSCM', fuse #21 in the underhood fuse block) for corrosion on its terminals and the fuse block slots. Perform a continuity and voltage drop test on the power (Red/White wire), ground (Black wire), and CAN bus wires (Tan and Tan/Black) between the PCM and FPCM.
   Typical fix: Clean the connector terminals and apply dielectric grease. If corrosion is severe, replace the connector pigtail. If the fuse block is corroded, it may need to be cleaned meticulously or replaced.
   Est. part cost: $15-$50 for a pigtail, $150-$300 for a fuse block.
3. General GMLAN Network Failure ⚪ Low Probability GM Technical Service Bulletin #08-07-30-021H addresses widespread communication issues on this platform due to wiring problems, particularly chafing or corrosion at the 16-way transmission harness connector and other inline connectors under the vehicle.
   How to confirm: Check for other 'U' codes (U0073, U0100, U0101, etc.) stored along with U0109. This indicates a broader network problem rather than an isolated FPCM issue. A scan tool showing multiple modules offline points to a network fault. On GMT900 trucks, the terminating resistors for the high-speed CAN bus are located in the ABS module (EBCM) and the airbag module (SDM), so a failure in one of those can take down the network.
   Typical fix: Diagnose the GMLAN network according to TSB #08-07-30-021H, which involves inspecting specific connectors and wiring harnesses for damage or corrosion. The transmission connector is a primary inspection point.
   Est. part cost: $0-$100 for wiring repairs.

Rare But Worth Checking

• Failed Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is very rare. Before condemning the PCM, all other possibilities, including wiring, grounds, and the FPCM itself, must be exhaustively ruled out.
• Bad OnStar Module (VCIM): In some documented cases, a failing OnStar module (VCIM) can disrupt the GMLAN network and cause a U0109 code, even though it seems unrelated. This is an unusual but possible cause if other diagnostics lead nowhere.

Diagnosis Steps

1. Scan for all DTCs in all modules. Note if other 'U' codes are present, which would suggest a wider network issue.
2. Locate the Fuel Pump Control Module (FPCM) on the driver's side frame rail cross-member, typically above the spare tire.
3. Inspect the FPCM and its electrical connector for physical damage, swelling, and corrosion (white, chalky powder on the module; green crust on the pins).
4. Check the fuse for the FPCM in the underhood fuse block (labeled 'FSCM' or similar, typically fuse #21, a 20A fuse). Carefully inspect the fuse and the terminals in the fuse block for corrosion, as this is a known failure point.
5. If the connector looks clean, use a multimeter to verify key-on power at Pin 13 (Dark Green/White), Pin 15 (Pink), and constant battery voltage at Pin 32 (Red/White). Check for a good ground at Pin 1 (Black).
6. With the battery disconnected, check the resistance of the GMLAN communication circuit at the DLC (pins 6 and 14) or the FPCM connector (between the Tan and Tan/Black wires). It should be approximately 60 ohms if the network is intact. A reading of 120 ohms indicates an open in the circuit or a missing termination resistor.
7. If power, ground, and communication circuits test good, the Fuel Pump Control Module is the most likely cause of the failure.
8. If other communication codes are present, follow the diagnostic procedures in TSB #08-07-30-021H, focusing on shared network connectors like the 16-way transmission plug and checking for chafed harnesses.

Parts You'll Likely Need

• Fuel Pump Control Module (FPCM) (OEM #25967325 (superseded by 20759945, 20850907)) — This module is the most common failure point for a U0109 code due to its vulnerable mounting location leading to corrosion and internal failure.
  Trusted brands: ACDelco (OEM, requires programming), Dorman OE FIX (Aftermarket, often pre-programmed)
  OEM price range: $120-$180
  Aftermarket price range: $70-$150
• FPCM Connector Pigtail — If the original connector is heavily corroded, simply replacing the module won't establish a reliable connection. A new pigtail is often required.
  Trusted brands: ACDelco, Dorman
  OEM price range: $30-$50
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P069E — This code specifically indicates a fault detected within the Fuel Pump Control Module, often appearing alongside the U0109 communication code as a direct result of the FPCM's internal failure.
• U0073 — This code means 'Control Module Communications Bus OFF' and indicates a general failure of the high-speed GMLAN network. If you see this with U0109, the problem is likely a shared network wiring issue, not just the FPCM.
• U0100 — Lost Communication with ECM/PCM. This often appears with other U-codes when there is a major network disruption, as described in TSB #08-07-30-021H.
• U0101 — Lost Communication with TCM. This points to the transmission connector being a potential source of the network failure, as highlighted in TSB #08-07-30-021H.

Technical Service Bulletins (TSBs) & Recalls

• 08-07-30-021H: Loss of High Speed GMLAN Communications, Intermittent No Crank, IP Gage Fluctuation, Various IP Warning Lamps Illuminated, Transmission May Not Shift, Communication DTCs U0073, U0100, U0101, U0102, U0109, U0121 or U0140 set.

Platform-Specific Known Issues

• TSB #08-07-30-021H documents that a loss of high-speed GMLAN communication (causing codes like U0109, U0073, U0100, etc.) can be caused by poor terminal connections or chafed wiring, especially at the main transmission harness connector.
• A very common secondary failure point is corrosion within the underhood fuse block at the terminals for the FPCM fuse (#21). A visual inspection of this fuse and its socket is critical.
• Owner Experience: Many owners successfully replace the FPCM themselves. A popular tip is to apply a thick layer of dielectric grease to the back of the new module and all over the connector to prevent future moisture intrusion. Some even fabricate a small shield or relocate the module to a drier location.

Mechanic-Grade Diagnostic Values

• GMLAN Bus Resistance — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates an open in the bus or one of the two terminating resistors is offline. A reading below 60 Ohms could indicate a shorted module on the bus.
• FPCM Connector Pin 32 (Red/White wire) Voltage — expected: Constant Battery Voltage (12V+). Failure: Low or no voltage indicates a problem with the power feed from the underhood fuse block (Fuse 21).
• FPCM Connector Pin 1 (Black wire) Ground — expected: Near 0 Ohms resistance to chassis ground.. Failure: High resistance indicates a corroded or broken ground connection.
• FPCM Connector Pin 15 (Pink wire) Voltage — expected: Ignition 1 Voltage (12V+ with key in ON/RUN position).. Failure: No voltage indicates a problem with the ignition-switched power supply.
• FPCM Connector Pin 13 (Dark Green/White wire) Voltage — expected: This is a 'Serial Data Enable' or 'Wake-Up' signal from the PCM. It should show voltage (3-12V) for a few seconds after key-on, or constantly while cranking.. Failure: No voltage at all on this pin points to a break in the wire between the FPCM and PCM, or a faulty PCM driver.

Scan Tool Commands That Help

• GM Tech 2 / GDS2: Fuel System / Fuel Pump Control Module Output Control — After confirming power and ground to the FPCM, use this bidirectional control to command the fuel pump on and off. This directly tests if the PCM can communicate with the FPCM and if the FPCM can command the pump, bypassing other inputs.
• GM Tech 2 / GDS2: Module Information / Data Display — To check if the FPCM is reporting its status to the network. If the module is completely offline, it will not respond. If it is online but has a fault, it may display data but also show internal fault codes like P069E.

Wiring & Ground Locations

• FPCM Connector — On the driver's side frame cross-member, above the spare tire.. This is the primary connection point for the module. It is highly exposed to road spray, causing corrosion on the pins for power, ground, and GMLAN communication, leading directly to code U0109.
• Underhood Fuse Block (Fuse 21) — Driver's side of the engine bay.. This fuse supplies constant battery power to the FPCM via the Red/White wire. The fuse terminals and the block itself are known to corrode from moisture intrusion, cutting power to the module and causing a U0109.
• GMLAN Terminating Resistors — The two 120-ohm resistors are internal to other modules. On this platform, they are typically located in the Electronic Brake Control Module (EBCM/ABS) and the Inflatable Restraint Sensing and Diagnostic Module (SDM/Airbag).. The GMLAN network requires exactly two 120-ohm resistors at its physical ends to function. If one of these modules fails or has a connector issue, the bus resistance will change from 60 ohms to 120 ohms, disrupting communication for all modules, including the FPCM.
• PCM Connector (Black Connector, Pin 50) — On the Powertrain Control Module (PCM) in the engine bay.. This pin sends the 'wake-up' signal to the FPCM via the Dark Green/White wire. If there is no signal from this pin, the FPCM will not activate, even if it has power and ground. This is the last-resort check before condemning the PCM itself.

Real Owner Repair Stories

• YouTube video by Phillip Bailey (2011 GM Truck) — Crank no start, U0109 code returned one day after replacing the Fuel Pump Control Module.
  ❌ Tried (didn't work) Replacing the Fuel Pump Control Module (FPCM).
  ✅ What actually fixed it The terminals for Fuse 21 in the underhood fuse block were corroded. Cleaning the fuse contacts provided a temporary fix, but the entire fuse block was ultimately replaced to ensure a reliable connection.
• Reddit user post on r/Silverado (2009 Chevy Silverado 1500 5.3L) — Initial electrical short in fuse block caused a no-crank. After replacing the fuse block, it would crank but not start. No fuel pump prime, code U0109.
  ❌ Tried (didn't work) Jumping starter relay (confirmed crank issue was separate)., Checking harness connectors at FPCM and PCM.
  ✅ What actually fixed it The user replaced the underhood fuse block due to an initial short, which then resolved the crank issue but revealed the U0109. The final fix was tracing the lack of power at fuse 21 and 20 back to the new (but possibly faulty) fuse block or a PCM issue, highlighting the fuse block as the central failure point.
• YouTube video by walosauto repair (2007 Chevy Silverado) — Intermittent stalling, U0109, new FPCM already installed by owner.
  ❌ Tried (didn't work) Replacing the Fuel Pump Control Module (FPCM).
  ✅ What actually fixed it The power feed to the FPCM (Red/White wire) only had 3 volts. The problem was traced to a poor connection at fuse #22 (in this specific video, though #21 is more common) in the underhood fuse box. The fuse legs were burnt/corroded, causing high resistance. Replacing the fuse and cleaning the terminals restored power.

When the Usual Fixes Don't Work

• In multiple documented cases, a vehicle presented with a U0109 code and a no-start condition even after the primary suspect, the Fuel Pump Control Module (FPCM), was replaced. The root cause was not the new module or the wiring harness near it, but rather corrosion on the terminals for the FPCM fuse (typically #21) inside the underhood fuse block. This creates a high-resistance connection, starving the new module of the power it needs to operate and communicate. Technicians who stop diagnosis after replacing the FPCM will miss this common secondary failure point.

OEM Part Supersession History

• 25967325 → 20759945, 20850907, 13501024 — Standard part evolution and updates by the manufacturer.
  Heads up: All genuine GM part numbers in this family require programming to the vehicle's VIN using dealer tools (Techline Connect). Some aftermarket suppliers sell pre-programmed or 'plug-and-play' units, but OEM parts do not come pre-programmed.