U0074 on 2014-2018 GMC Sierra 3500: Communication Bus Failure Causes and Fixes

What's Unique About the 2014-2018 Gmc SIERRA 3500

On the 2014-2018 GMC Sierra (K2XX platform), this code has a well-documented history. GM Technical Service Bulletins (TSBs) specifically point to a loss of communication on the 'Powertrain Expansion Bus', a dedicated network between the Engine Control Module (ECM) and the Fuel Pump Control Module (FPCM), as a common cause. This communication failure is known to trigger a secondary, misleading code, P2635 (Fuel Pump Flow Performance), which can cause technicians to mistakenly suspect the fuel pump itself. The root cause is almost always the network failure, not the component implicated by the secondary code. Furthermore, this platform is known for specific wiring chafe points and a problematic G218 ground stud that can trigger this code.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on.
• "Service StabiliTrak" or "Service Power Steering" warnings on the Driver Information Center (DIC).
• Loss of power steering, which may be intermittent.
• Engine may run rough, stall, or fail to start.
• Multiple other warning lights may be on simultaneously (ABS, Airbag, Traction Control).
• Gauges on the instrument cluster may behave erratically or drop to zero.
• Radio or infotainment screen may go blank or reset.

Most Likely Causes

1. Wiring Harness Damage 🔴 High Probability The K2XX platform has several known harness chafe points. Vibration and exposure cause wires to rub through their insulation, leading to shorts. Common failure spots include: the harness along the driver's side frame rail near the FPCM, the harness rubbing the battery tray support bracket (per TSB 23-NA-074), the harness over the transmission bellhousing, and near the driver's side upper control arm (per TSB 20-NA-214).
   How to confirm: Visually inspect the wiring harness in the known problem areas. This may require removing the driver's side wheel and wheelhouse liner for access. Look for chafed insulation, broken wires, or green/white corrosion in connectors, especially the FPCM and EBCM connectors.
   Typical fix: Repair the damaged section of wire using solder and heat-shrink tubing. Replace corroded connector pigtails. Protect the repaired harness with high-quality loom or anti-abrasion tape and re-route it away from sharp edges.
   Est. part cost: $10-$50
2. Poor Ground Connection (G218) 🔴 High Probability TSB PIT5405C specifically identifies the G218 ground stud as a source of numerous electrical issues. The factory sometimes traps the dash insulator mat under the ground eyelet, preventing a solid connection and causing intermittent voltage drops that disrupt module communication.
   How to confirm: Locate G218 under the driver's side dashboard, behind the A-pillar/kick panel trim. Check if the nut is loose or if the black dash insulation is caught under the connector. A voltage drop test performed by a technician can confirm the poor ground.
   Typical fix: Remove the nut, cut away the interfering insulation mat, clean the stud and eyelet surfaces, and securely retighten the nut. 🎬 Watch: How to fix the G218 ground issue yourself.
   Est. part cost: $0-$5
3. Faulty Fuel Pump Control Module (FPCM) 🟡 Medium Probability → Shop Fuel Pump The FPCM is a known point of failure and its loss of communication is specifically cited in GM service bulletin PIP5427B for this code. However, many owners replace it only to find the true fault was in the wiring to the module.
   How to confirm: After verifying wiring and grounds are intact, disconnect the FPCM. If communication is restored to other modules on the bus, the FPCM is likely faulty. This is an advanced diagnostic step best done with a proper scan tool.
   Typical fix: Replace the FPCM. The new module must be programmed to the vehicle using dealer-level software. 🎬 See this walkthrough for replacing the fuel pump control module.
   Est. part cost: $70-$180
4. Faulty Electronic Brake Control Module (EBCM) 🟡 Medium Probability → Shop ABS Control Module The EBCM is a key module on the chassis CAN bus and contains one of the network's terminating resistors. An internal failure or corrosion in its main connector from water intrusion can disrupt the entire network.
   How to confirm: After verifying wiring, disconnect the EBCM and see if communication is restored. Inspect the connector pins for any signs of green or white corrosion. A professional scan tool can help identify which modules are offline.
   Typical fix: Replace the EBCM. This part requires programming and a brake pedal position sensor calibration by a dealer or qualified shop.
   Est. part cost: $250-$600
5. Termination Resistor Failure ⚪ Low Probability On these trucks, an external 120-ohm resistor is often located in the harness above the spare tire, taped to the harness near the FPCM. It is exposed to the elements and can fail, or the wiring to it can break.
   How to confirm: Using a multimeter, measure the resistance between CAN High (Pin 6) and CAN Low (Pin 14) at the OBD-II port. A healthy network should read approximately 60 ohms. A reading of 120 ohms indicates a missing or failed termination resistor or an open in the circuit.
   Typical fix: Replace the faulty resistor (it is a small, plug-in component) or repair the wiring leading to it.
   Est. part cost: $20-$100

Rare But Worth Checking

• Poor Ground Connection at G402: A poor ground at the G402 location, at the rear of the vehicle frame near the spare tire, can specifically affect the Fuel Pump Control Module (FPCM) and trigger U0074 with P2635.

Diagnosis Steps

1. Connect a professional scan tool (like GM GDS2) and perform a network test. Identify which modules are not communicating.
2. Check for other DTCs, paying special attention to P2635 and U18A2. Per TSB #PIP5427B, always prioritize diagnosis of U0074 first.
3. With the ignition off and battery disconnected, measure resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. The reading should be ~60 ohms. 120 ohms indicates an open/missing terminator; ~0 ohms indicates a short.
4. Perform a thorough visual inspection of the wiring harness, especially at known chafe points: along the driver's side frame rail, near the battery tray, over the transmission, and around the EBCM.
5. Inspect the G218 ground stud under the driver's dash kick panel. Check for a loose nut or trapped insulation mat as described in TSB PIT5405C.
6. Inspect the EBCM connector for any signs of water intrusion or pin corrosion.
7. If wiring and grounds are good, begin isolating modules. Disconnect a suspect module (like the FPCM), and re-check if communication is restored to the rest of the network. If it is, the disconnected module is likely faulty.
8. For advanced diagnosis, use an oscilloscope to check the CAN bus waveform at the OBD-II port for proper signal, shorts to power/ground, or reflections.
🎬 Watch: Professional diagnostic steps for U0074 and P2635 codes.

Parts You'll Likely Need

• Fuel Pump Control Module (FPCM) (OEM #23453289) — This module is a common failure point and is directly implicated in TSBs related to code U0074. However, it is often replaced unnecessarily when the real fault is in the wiring.
  Trusted brands: ACDelco, Dorman
  OEM price range: $100-$180
  Aftermarket price range: $70-$120
• Electronic Brake Control Module (EBCM) (OEM #23380704) — The EBCM is a central hub on the chassis network and contains a terminating resistor. An internal fault or connector corrosion can take down the bus. This part number supersedes 23154722.
  Trusted brands: ACDelco
  OEM price range: $250-$600
  Aftermarket price range: $200-$450

Related Codes That Often Appear With This One

• P2635 — This 'Fuel Pump Flow Performance' code is often triggered as a direct result of the ECM losing communication with the Fuel Pump Control Module (FPCM) due to the U0074 fault. The ECM defaults to a state that can cause higher-than-desired fuel pressure.
• U18A2 — Another communication code related to the FPCM ('Lost Communication With Fuel Pump Control Module On Private Bus'). TSB #PIP5427B states that U0074 should be diagnosed first if both are present.
• U0121 — Lost Communication with the Anti-Lock Brake System (ABS) Control Module. This can occur if the fault is on the chassis bus where the EBCM resides or if the EBCM itself has failed.

Technical Service Bulletins (TSBs) & Recalls

• PIP5427B: Diagnostic tips for SES light with DTCs P2635, U0074 and/or U18A2 set. Stresses that U0074 must be diagnosed first.
• PIT5405C: Addresses various electrical concerns (including communication issues) caused by a poor G218 ground connection.
• 20-NA-214: Details specific engine wiring harness chafe points near the ECM/TCM bracket, upper control arm, and shock tower.
• 18-NA-161: Addresses high resistance in battery jumper cables or ground cables as a potential cause for communication issues.

Platform-Specific Known Issues

• Per TSB #PIP5427B, a loss of communication between the ECM and FPCM is a known issue that can set U0074 and P2635. The bulletin stresses that communication DTCs must be diagnosed before P2635, as replacing fuel system parts will not resolve the issue.
• Per TSB #PIT5405C, the G218 ground under the driver's dash is a common source of electrical faults. The dash insulator mat gets trapped under the ground eyelet, causing a poor connection that leads to communication codes and other strange electrical behavior.
• Per TSB #20-NA-214, the engine wiring harness is known to chafe against the ECM/TCM bracket, the driver's side upper control arm, and the shock tower bolt, causing shorts that can trigger U0074.

Mechanic-Grade Diagnostic Values

• CAN Bus Resistance at DLC — expected: ~60 Ohms. Failure: A reading of ~120 Ohms indicates an open circuit or missing terminating resistor. A reading near 0 Ohms indicates a short between the CAN High and Low wires.
• CAN Bus Voltage (Normal Operation) — expected: CAN High and CAN Low should show clean, square waves on an oscilloscope. Both lines should read around 2.5V at rest, with CAN High rising to ~3.5V and CAN Low dropping to ~1.5V during communication.. Failure: A distorted or mirrored signal, or a steady voltage with no differential (e.g., both lines stuck at 2.457V) indicates a network fault or a failed module driver.
• FPCM Fuel Pump Command Signal (at FPCM connector) — expected: Using a test light on the Dark Green/White wire (Pin 13), the light should illuminate for 3-6 seconds with the key on, or constantly while cranking.. Failure: No power on the Dark Green/White wire indicates a break in the wire from the ECM or a failed ECM driver.
• FPCM Fuel Pump Supply Voltage (at FPCM connector) — expected: By jumping Pin 32 (Battery Positive Voltage) to Pin 47 (Fuel Pump Supply Voltage), the fuel pump should run continuously.. Failure: If the pump does not run when jumped, and the main power/ground to the FPCM are good, the fuel pump itself is likely faulty.

Scan Tool Commands That Help

• GM GDS2: Vehicle DTC Information / Network Test — This is the first diagnostic step to get a vehicle-wide list of all modules and see which ones are not communicating, which is essential for isolating a U-code fault.
• GM GDS2: Module Diagnostics > [Module Name] > Control Functions — After identifying which modules are offline, this function can be used to test the functionality of the *remaining* online modules. This helps verify the integrity of the rest of the network.
• GM GDS2: Module Replacement & Programming — This function is required after replacing network-critical modules like the FPCM or EBCM to download the correct software and configure the new module for the vehicle.

Wiring & Ground Locations

• G218 — Under the driver's side dashboard, behind the A-pillar/kick panel trim, near the speaker.. This is a major instrument panel ground. TSB PIT5405C notes that the dash insulator mat often gets trapped under the ground nut, causing a high-resistance connection that leads to intermittent network failures and multiple communication codes.
• Terminating Resistor — Taped to the main wiring harness, located above the spare tire, often near the FPCM.. This external 120-ohm resistor is one of two required for the CAN bus to function. If it fails or its wiring is damaged, the total bus resistance will read 120 ohms instead of the correct 60 ohms, stopping communication.
• FPCM Connector — On the Fuel Pump Control Module, which is mounted to the driver's side frame rail, typically near the fuel tank.. This connector is exposed to road spray and debris, making it highly susceptible to corrosion. A broken wire or corroded pin at this connector is a very common cause of U0074, especially when paired with P2635.
• EBCM Connector — On the Electronic Brake Control Module, located in the engine bay on the driver's side, attached to the ABS hydraulic block.. The EBCM is a primary node on the chassis CAN bus and contains a terminating resistor. Corrosion from water intrusion into this connector or an internal module fault can take down the entire network.
• Connector Under Passenger Seat — A large inline wiring harness connector located under the front passenger seat.. This connector is a junction point for the CAN bus circuit running between the front of the truck (ECM) and the rear (FPCM). In some documented cases, simply being disturbed during interior work was enough to cause a poor connection, triggering U0074. Reseating it fixed the issue.

Real Owner Repair Stories

• SilveradoSierra.com user (2015 Silverado) — U0074 with a blank radio screen and StabiliTrak warnings.
  ❌ Tried (didn't work) Not specified, diagnosis went straight to wiring inspection.
  ✅ What actually fixed it A single corroded wire was found and repaired within the main harness near the Fuel Pump Control Module (FPCM) above the spare tire.
• iATN (International Automotive Technicians Network) post (2015 Silverado 1500 4.3L V6) — Check Engine Light with codes U0074, U18A2, and P2635. Scan tool showed actual fuel pressure was much higher than desired.
  ❌ Tried (didn't work) Initial diagnosis confirmed wiring resistance on the Powertrain Expansion bus was correct.
  ✅ What actually fixed it The technician found that while resistance was good, the ECM was not generating the necessary CAN bus voltage signal (both lines were stuck at 2.457V). Replacing the ECM resolved the communication failure.
• YouTube channel 'Global Commerce CA' (2023 Chevy Silverado (similar K2XX diagnostic principles)) — U0074, U0103, no communication with multiple modules.
  ❌ Tried (didn't work) Initial troubleshooting was difficult due to wiring diagram differences on the newer model year.
  ✅ What actually fixed it The issue was traced to a poor connection in a large inline connector located under the passenger seat. Simply disconnecting and reconnecting the connector restored all communication and cleared the codes.

OEM Part Supersession History

• 23154722 → 23380704 — Part revision by manufacturer for the Electronic Brake Control Module (EBCM).