U0074 on 2015-2018 Chevrolet Suburban: Causes and Fixes for Bus Communication Failure

What's Unique About the 2015-2018 Chevrolet SUBURBAN

For the 11th generation Suburban and its K2XX platform mates, GM utilizes multiple specific CAN buses. TSBs for this platform clarify that U0074 can point to a failure on the 'Chassis bus' (involving brakes and steering) or a communication breakdown on the dedicated 'Powertrain Expansion Bus' between the Engine Control Module (ECM) and the Fuel Pump Control Module (FPCM). Unlike generic interpretations, on this vehicle U0074 is a high-priority code that must be diagnosed before other related codes, such as P2635 (Fuel Pump Flow Performance), as the network failure is often the root cause.

Diagnostic Flowchart

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

Symptoms You May Notice

• Service StabiliTrak message on the dash.
• Service Power Steering / Power Steering Assist is Off message
• ABS and Traction Control warning lights illuminated.
• Check Engine Light on.
• Loss of power steering assist, making steering very difficult
• Fuel gauge reading empty or inaccurately when fuel is in the tank.
• Erratic or harsh transmission shifting
• Cruise control inoperative.

Most Likely Causes

1. Damaged or Corroded Wiring Harness 🔴 High Probability Wiring harnesses on the K2XX platform are known to chafe in specific locations. The harness for the Electronic Brake Control Module (EBCM) can rub against the frame or other components in the engine bay. The harness to the Fuel Pump Control Module (FPCM) near the spare tire is also a common trouble spot. TSB 23-NA-074 also points to wire chafing on the battery tray support bracket.
   How to confirm: Visually inspect harnesses connected to the EBCM, PSCM, and FPCM for chafing, breaks, or corrosion. Pay close attention to where the harness bends or is secured near metal brackets. Check resistance between CAN High (Pin 6) and CAN Low (Pin 14) at the OBD-II port; a reading of ~60 ohms is healthy, while ~120 ohms indicates an open circuit or a missing terminating resistor.
   Typical fix: Repair the damaged section of the wiring harness using solder and heat shrink, then protect it with loom or by rerouting it. 🎬 See how to properly solder and shrink-wrap damaged harness wires. Clean corroded connectors with electrical cleaner and apply dielectric grease.
   Est. part cost: $10-$100
2. Failed Control Module (ECM, EBCM, FPCM) 🟡 Medium Probability An internal failure in any module on the bus can cause it to stop communicating or send corrupt data, taking the entire network down. The EBCM is a very common point of failure, causing StabiliTrak and ABS warnings. The ECM can also fail, causing the U0074/P2635 combination.
   How to confirm: This requires a professional scan tool to identify which module is not responding. A technician may disconnect modules one by one while monitoring bus resistance to see if communication is restored.
   Typical fix: Replace the faulty control module. Most modules, like the ECM or EBCM, require programming to the vehicle's VIN after installation using dealer-level software.
   Est. part cost: $300-$1200
3. Low Battery Voltage or Poor Ground Connection ⚪ Low Probability → Shop Vehicle Battery Control modules are sensitive to voltage. A weak battery, failing alternator, or corroded ground strap can cause unpredictable communication errors, sometimes setting a U0074 code. These trucks have complex electrical demands that can expose a weak battery.
   How to confirm: Test the battery voltage at rest (should be >12.4V). Check the charging system output (typically 13.7-14.7V). Inspect and clean the main battery terminals, engine block, and chassis ground connections.
   Typical fix: Charge or replace the battery. Clean or replace corroded terminals or ground straps.
   Est. part cost: $5-$300

Rare But Worth Checking

• Faulty Terminating Resistor: The CAN bus has two 120-ohm terminating resistors. One is typically inside the ECM. On some K2XX trucks, the second resistor is not in a module but is a separate, serviceable plug taped to the harness near the Fuel Pump Control Module (FPCM) above the spare tire. If this resistor fails or its connector corrodes, the bus resistance will read 120 ohms instead of 60, causing a U0074.
• Improperly Installed Aftermarket Accessories: Tapping into CAN bus wires for accessories like remote starters, aftermarket lighting, or alarms can introduce interference and bring down the network. These should be removed as a first step in diagnosis.

Diagnosis Steps

1. Verify battery health and ensure voltage is stable and above 12.4V at rest.
2. Use a professional scan tool to read codes from ALL vehicle modules, not just the ECM. Note which modules are not communicating.
3. Prioritize diagnosis of U0074 before any other codes, as per GM Technical Service Bulletin PIP5427B.
🎬 Watch this diagnostic walkthrough of the U0074 and P2635 codes.
4. With the key off and battery disconnected, measure the resistance between Pin 6 (CAN High) and Pin 14 (CAN Low) at the OBD-II port. A healthy bus should read approximately 60 ohms. A reading of 120 ohms indicates an open circuit or a problem with one of the two terminating resistors. A reading near 0 ohms indicates a short between the high and low lines.
5. Visually inspect all related wiring harnesses, especially the common chafe points: around the EBCM, near the battery tray support bracket, and the harness leading to the FPCM above the spare tire.
6. If wiring looks good, the issue is likely a failed module. This requires advanced diagnostics, often by disconnecting modules one by one to isolate the faulty component. This step is best left to a professional.

Parts You'll Likely Need

• Engine Control Module (ECM) (OEM #12673525 (Example for 2016 5.3L, verify by VIN)) — The ECM can fail internally, causing a loss of communication with other critical modules like the FPCM, triggering U0074. It also contains one of the bus terminating resistors.
  Trusted brands: ACDelco
  OEM price range: $400-$800
  Aftermarket price range: $250-$500
• Electronic Brake Control Module (EBCM) (OEM #84102241 / 84778358 (Examples for 2016, verify by VIN)) — The EBCM is a key node on the chassis bus. An internal fault can take down the network, causing StabiliTrak and ABS warnings alongside the U0074 code. This is a very common failure point. 🎬 Watch this step-by-step guide to replacing the ABS EBCM module.
  Trusted brands: ACDelco
  OEM price range: $350-$700
  Aftermarket price range: $200-$450
• Wiring Harness Connector/Pigtail — If corrosion or physical damage is found at a module connector (especially the EBCM), replacing the connector pigtail is often the most reliable repair.
  Trusted brands: ACDelco, Dorman
  OEM price range: $40-$80
  Aftermarket price range: $20-$50

Related Codes That Often Appear With This One

• P2635 — This fuel pump performance code is often triggered by the ECM losing communication with the Fuel Pump Control Module (FPCM) due to the U0074 fault on the Powertrain Expansion Bus.
• U18A2 — Another communication code that often appears with U0074. TSB PIP5427B states that U0074 diagnosis should take priority as it indicates a more severe bus-off condition.
• C0186, C0196, C0287 — These are chassis-related codes (yaw rate sensor, lateral accelerometer) that may set when the Electronic Brake Control Module loses communication on the chassis bus, flagged by U0074.

Technical Service Bulletins (TSBs) & Recalls

• PIP5427B: Advises prioritizing U0074 diagnosis when set with P2635 or U18A2, pointing to an ECM/FPCM communication loss.
• PIT5076E: Recommends diagnosing the Chassis bus when U0074 appears with various C-codes and U-codes related to the brake and steering systems.
• 23-NA-074: Points to wire harness chafing against the battery tray support bracket as a potential cause for U0074 and other communication DTCs.

Platform-Specific Known Issues

• TSB #PIP5427B highlights that when U0074 is set with P2635 (Fuel Pump Performance) and/or U18A2, the U0074 code must be diagnosed first. The root cause is often a loss of communication between the ECM and the Fuel Pump Control Module (FPCM), not a faulty fuel pump.
• TSB #PIT5076E instructs technicians to diagnose the 'Chassis bus' when U0074 is found with various brake and steering module codes, pointing towards a network issue affecting the EBCM or PSCM.
• TSB #23-NA-074 (supersedes PIT5847H) identifies a condition where the engine wiring harness can chafe on the battery tray support bracket, causing a host of communication and sensor codes, including U0074.

Mechanic-Grade Diagnostic Values

• High-Speed CAN Bus Voltage (CAN High) — expected: Approx. 2.5V in recessive state, 3.5V in dominant state (measured to ground).. Failure: Voltage stuck high, low, or at 0V indicates a short or open circuit.
• High-Speed CAN Bus Voltage (CAN Low) — expected: Approx. 2.5V in recessive state, 1.5V in dominant state (measured to ground).. Failure: Voltage stuck high, low, or at 0V indicates a short or open circuit.
• FPCM Fuel Pump Command Signal (at FPCM connector) — expected: On the Dark Green/White wire (Pin 13), a test light should illuminate for 3-6 seconds with key-on, or constantly during cranking.. Failure: No voltage signal on this wire indicates a problem with the ECM or the wiring from the ECM.
• Terminating Resistor Value — expected: Approx. 120 ohms when measured across its two pins.. Failure: An open reading (OL) or significantly different resistance indicates a failed resistor.

Scan Tool Commands That Help

• GDS2 (GM Dealer Tool): Module Status / Communication Check — To see a list of all expected control modules on the network and identify which specific modules are not responding. This is a primary step in isolating the source of the U0074 code.

Wiring & Ground Locations

• Serviceable Terminating Resistor — Taped to the main wiring harness above the spare tire, near the Fuel Pump Control Module (FPCM) and above the muffler.. This is one of the two 120-ohm terminating resistors for the high-speed CAN bus. If it fails or its connector corrodes, the total bus resistance will be incorrect (reading 120 ohms instead of 60), causing a U0074 fault.
• G103 / G104 — G103 is on the passenger side front of the cylinder head. G104 is on the driver's side rear corner of the engine, mounted to the cylinder head.. These are primary engine and module grounds. A loose or corroded connection at these points can interrupt power to critical modules like the ECM, causing communication codes.
• EBCM Connector (X1) — Attached to the ABS hydraulic block in the engine compartment, typically on the driver's side frame rail.. This is the main 38-pin connector for the EBCM. A fault here directly impacts the chassis CAN bus. The high-speed CAN lines are pins 12 (TAN/BLK) and 13 (TAN).
• Frame Grounds (Behind Front Wheels) — On the frame, located directly behind both front wheels.. These grounds are in a terrible location prone to water and salt spray, leading to corrosion that can cause intermittent and difficult-to-diagnose electrical issues, including network faults.

Real Owner Repair Stories

• 2CarPros Forum User (GM Truck (platform similar to Suburban)) — No communication with Fuel Pump Control Module, 1.4 volts on the main power wire at the module connector.
  ❌ Tried (didn't work) Initial check of fuses and grounds appeared fine.
  ✅ What actually fixed it Found a broken power wire inside the wiring loom. The break was located where the harness makes a turn in the square tube of the truck frame, right under the driver's side fuse panel. Running a jumper wire around the damaged section restored power and fixed the issue.

OEM Part Supersession History

• 85534834, 85534835, 85534836 → 88988999 — Part consolidation and revision by GM.
  Heads up: This is the part number for the serviceable Data Link LAN Terminator Resistor.

Model Year Variations Within This Range

• 2015-2018: While mechanically similar, there were minor technology and feature updates. The 2017 model year introduced more advanced driver-assist features, potentially adding complexity to the CAN bus networks compared to the 2015 models. However, the core architecture and common failure points for U0074 remain consistent across this year range.