U0109 on 2013-2015 Cadillac ATS: Lost Communication With Fuel Pump Control Module Causes and Fixes

What's Unique About the 2013-2015 Cadillac ATS

For this specific generation of Cadillac ATS and its platform mates, the U0109 code is strongly associated with a known wiring harness issue. A General Motors Technical Service Bulletin (TSB PIC4740E) points directly to a poor fit or loose terminals in the main transmission harness connector (X1) as the root cause for a host of communication codes, including U0109. This connector serves as a major junction for numerous data lines, and a fault there can disrupt the entire network. The TSB also specifically advises inspecting the harness securing bracket on the passenger side of the bell housing for potential chafing on the ATS. This known issue often leads to a misdiagnosis where the FPCM is replaced unnecessarily.

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 while driving.
• Check Engine Light is on.
• No audible fuel pump whine from the rear of the vehicle when the key is turned to the 'ON' position.
• Reduced engine power or rough running if the engine does start.
• Other warning lights, such as for the StabiliTrak system, may be illuminated due to the widespread communication issue. [Bulletin #PIC4740E]

Most Likely Causes

1. Poor Connection at Transmission X1 Harness Connector 🔴 High Probability → Shop Transmission Assembly As documented in TSB #PIC4740E, the GMLAN communication wires for the FPCM and other modules pass through this connector, which is susceptible to loose pins or fretting corrosion. Its location on the transmission subjects it to vibration and potential moisture.
   How to confirm: Visually inspect the large X1 connector on the driver's side of the transmission. Disconnect it and check for any gray/white film (fretting corrosion), backed-out pins, or moisture. Carefully tug on individual wires to ensure pins are fully seated.
   Typical fix: Clean the connector pins with a dedicated electrical contact cleaner, apply a small amount of dielectric grease to the seal, and ensure it is securely reconnected.
   Est. part cost: $5-$15 for cleaner and grease
2. Failed Fuel Pump Control Module (FPCM) 🟡 Medium Probability → Shop Fuel Pump
   How to confirm: After confirming the wiring, fuse, and grounds are good, the module itself is the likely culprit. A professional scan tool may be able to communicate directly with the FPCM; if it cannot, and power/ground are verified at the module, it has likely failed.
   Typical fix: Replace the Fuel Pump Control Module. The new module MUST be programmed by a dealer or a qualified shop with the correct software for your vehicle's VIN.
   Est. part cost: $150-$250
3. Blown Fuel Pump/FPCM Fuse ⚪ Low Probability → Shop Fuel Pump
   How to confirm: Locate the rear fuse block (in the trunk area) and check the fuse for the FPCM, typically a 20A fuse. A visual inspection or a multimeter can confirm if it's blown.
   Typical fix: Replace the blown fuse. If the fuse blows again, it indicates a short circuit in the wiring or the FPCM that needs further diagnosis.
   Est. part cost: $1-$5
4. Damaged Wiring or Poor Ground ⚪ Low Probability TSB PIC4740E specifically mentions checking for harness chafing at the securing bracket on the passenger side of the transmission bell housing on the ATS.
   How to confirm: Visually inspect the wiring harness leading to the FPCM (located in the trunk) for any signs of chafing, breaks, or rodent damage. Also inspect the harness near the transmission as noted in the TSB. Use a multimeter to check for a solid ground connection at the FPCM connector.
   Typical fix: Repair the damaged section of the wire or clean and secure the ground connection point.
   Est. part cost: $10-$50 for wiring repair supplies

Rare But Worth Checking

• Faulty OnStar Module (VCIM):

Diagnosis Steps

1. Scan for all DTCs in all available modules. Note any other 'U' codes, as a group of them strongly points to a network-wide problem originating from a connector or wiring fault.
2. Turn the key to the 'ON' position (without starting) and listen for a 2-second hum from the rear of the car. An absence of this sound suggests the fuel pump is not priming.
3. As per TSB #PIC4740E, the first and most crucial step is to locate and inspect the transmission X1 connector on the driver's side of the transmission.
4. Disconnect the X1 connector and check for loose or backed-out terminals, corrosion, or moisture. Clean with electrical contact cleaner and apply dielectric grease before reconnecting securely.
5. Per the TSB, also inspect the wiring harness for chafing where it is secured by a bracket on the passenger side of the transmission bell housing.
6. Check the FPCM fuse (typically 20A) in the rear fuse block.
7. If the connector and fuse are good, locate the FPCM. Its location is debated; check both the driver's and passenger's side of the trunk, behind the trim or under the floor carpeting. Inspect its connector and the surrounding wiring for damage.
8. Using a multimeter, verify that the FPCM is receiving battery voltage and has a solid ground connection.
9. If all wiring, connectors, and power/ground are confirmed to be good, the FPCM itself is the most likely failed component.
10. If replacing the FPCM, the new module must be programmed by a qualified technician.

Parts You'll Likely Need

• Fuel Pump Control Module (OEM #23488511, 22872265, 22872266 (Verify with VIN)) — If wiring and connectors are confirmed good, the module itself is the next logical point of failure. It controls the fuel pump and its failure will cause a no-start or stall.
  Trusted brands: ACDelco (GM Genuine), Dorman, Wells
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• Electrical Contact Cleaner and Dielectric Grease — These are needed for the most common fix: cleaning the transmission X1 connector to resolve the communication fault.
  Trusted brands: CRC, Permatex
  Aftermarket price range: $10-$20

Related Codes That Often Appear With This One

• U0073 — Control Module Communication Bus 'A' Off. This code, along with many others, is listed in TSB #PIC4740E and points towards a general network failure, often caused by the X1 connector issue. [Bulletin #PIC4740E]
• U0100 — Lost Communication with ECM/PCM. Its presence with U0109 points to a broader network issue, reinforcing the likelihood of a harness or connector fault rather than a single module failure.
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module. This is another code cited in TSB #PIC4740E, strongly suggesting the transmission X1 connector is the root cause. [Bulletin #PIC4740E]
• P069E — Fuel Pump Control Module Requested MIL Illumination. This code may be stored in the ECM when the FPCM detects an internal problem and requests the Check Engine Light to be turned on. It is a common companion to U0109.

Technical Service Bulletins (TSBs) & Recalls

• PIC4740E: Addresses multiple communication DTCs, including U0109. Directs technicians to inspect the transmission X1 connector for loose or poor-fitting terminals and to check for harness chafing near the bell housing on the ATS.

Platform-Specific Known Issues

• A known issue, documented in GM TSB #PIC4740E, involves poor terminal fit in the transmission X1 connector, causing U0109 and a host of other communication codes. This should be the first place to check.
• The same TSB also calls for an inspection of the wiring harness for chafing at a securing bracket near the transmission bell housing on the ATS.

Mechanic-Grade Diagnostic Values

• FPCM Power Supply Voltage — expected: Battery Voltage (approx. 12.6V with key on). Failure: Voltage below 12V or 0V indicates a power supply issue.
• FPCM Ground Connection — expected: Less than 0.2 Ω resistance to a known good chassis ground.. Failure: High resistance (OL) indicates a bad ground connection.
• Fuel Pump Enable Signal from ECM — expected: 12V for 2-6 seconds with key on, or constant 12V while cranking.. Failure: No voltage at the FPCM indicates a break in the wire or a faulty ECM.
• GMLAN Bus Resistance — expected: Approximately 60 Ω across the High-Speed GMLAN lines.. Failure: A reading of 120 Ω suggests one of the two terminating resistors is offline. A reading of 0 Ω indicates a short between the lines.

Scan Tool Commands That Help

• GDS2 (GM Dealer Scan Tool): Fuel Pump Control Module Data Display — To check if the scan tool can communicate with the FPCM at all. If it can't, it points strongly to a network, power, or ground issue. If it can, you can monitor parameters like 'Fuel Pump Commanded Speed' vs 'Actual Speed'.
• GDS2 (GM Dealer Scan Tool): Fuel Pump On/Off Command — This is a bidirectional test to directly command the FPCM to turn the fuel pump on. If the pump runs with this command, it confirms the FPCM and the pump itself are likely functional, pointing the diagnosis towards the communication line or ECM.
• GDS2 (GM Dealer Scan Tool): Module Diagnostics > Body Control Module > Power Mode > Transport Mode — In rare cases, a vehicle stuck in 'Transport Mode' can disable non-essential modules to save battery, potentially including the FPCM. A flashing red battery light is an indicator. This function allows a technician to disable the mode.

Wiring & Ground Locations

• FPCM (Fuel Pump Control Module) — Located in the trunk. Sources conflict on the exact side, with some stating the driver's side near the rear suspension and others the passenger's side by the wheel well. It is often bolted to the frame rail.. This is the module that has lost communication. All power, ground, and network tests are performed at its connector.
• FPCM Connector — On the FPCM module itself.. Key test point. Pin 1 is Ground (Black), Pin 32 is Battery Power (Red/White), Pin 13 is the command signal from the ECM (Dark Green/White), and Pins 6 (Tan/Black) & 7 (Tan) are the GMLAN communication lines.
• G406 Ground Point — Described as being on the upper middle of the right rear wheel well on a 2014 model.. This is a major body ground point near the FPCM. A poor connection here can cause intermittent power and communication issues for the fuel system electronics.
• X1 Transmission Connector — Large wiring harness connector located on the driver's side of the transmission.. This is the primary suspect identified in TSB #PIC4740E. The GMLAN communication wires for the FPCM pass through this connector, and it is a common failure point for corrosion and loose pins.
• ECM (Engine Control Module) Pin 50 — In the black connector at the ECM. It is the Dark Green/White wire.. This is the source of the fuel pump enable signal. If there is no power on this wire at the FPCM, checking for 12V here can determine if the fault is in the wiring harness or the ECM itself.

Real Owner Repair Stories

• YouTube channel 'Pine Hollow Auto Diagnostics' (2015 Cadillac CTS (platform-mate with similar wiring architecture)) — Check Engine Light with codes P069E (FPCM related) and P151E.
  ❌ Tried (didn't work) Initial diagnosis pointed towards the FPCM due to the P069E code.
  ✅ What actually fixed it The actual cause was a broken wire leading to the active grille shutter. On this platform, the FPCM is integrated into a larger chassis control module that also controls the grille shutter. The broken shutter wire caused the entire module to set a fault, which misleadingly reported as an FPCM problem. The fix was to repair the broken wire in the harness near the front bumper.

OEM Part Supersession History

• 22872265, 22872266 → 23488511 — Standard part revision and consolidation by the manufacturer.
  Heads up: Part number 23488511 is listed as compatible with 2013-2019 ATS models. Always verify the correct part number with the vehicle's VIN before ordering.