U0401 on 2015-2018 GMC Yukon: Invalid ECM Data Causes & Fixes

What's Unique About the 2015-2018 Gmc YUKON

For this generation of GMC Yukon (K2UG platform), the U0401 code is frequently tied to specific, well-documented wiring issues. Unlike many vehicles where this code leads to guesswork, GM has issued multiple Technical Service Bulletins (TSBs) pointing to exact locations where wiring harnesses are known to chafe and short out. The primary spots are under the driver/passenger door sill plates (TSB #PIT5457C) and where the chassis harness passes over the frame near the spare tire (TSB #PIT5556A). This makes diagnosis more direct, as a physical inspection of these areas is a primary step. Another known issue is a poor ground at G218, where the dash insulator mat can interfere with the BCM ground connection.

Diagnostic Flowchart

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

Generation note: The 2015-2018 model years all fall within the fourth generation of the GMC Yukon (K2UG platform), which is part of the larger GM K2XX platform. The issues described are common across this entire generation and its platform mates like the Chevrolet Tahoe/Suburban and Cadillac Escalade.

Symptoms You May Notice

• "Service Stabilitrak" message on the driver information center (DIC)
• "Service Power Steering" or "Steering Assist is Reduced" message on the DIC
• Illuminated Check Engine Light
• Traction control light is on
• Intermittent stalling at stops
• Harsh or erratic transmission shifting
• "Shift to Park" message may appear
• Instrument panel gauges fluctuating erratically
• Backup camera inoperative or "Rear Vision System Unavailable" message

Most Likely Causes

1. Damaged Wiring Harness Under Sill Plates 🔴 High Probability As documented in GM TSB #PIT5457C, the wiring harness running along the floor under the driver and/or passenger door sill plates is susceptible to damage. Specifically, the Communication Enable circuit (5986) can develop high resistance, an open, or a short, disrupting communication to multiple modules.
   How to confirm: Remove the plastic sill plates and peel back the carpet to physically inspect the entire length of the wiring harness for chafed, broken, or corroded wires. A voltmeter can be used to check for low or no voltage on circuit 5986 at an affected module (like the EBCM or PSCM) when the issue occurs.
   Typical fix: Repair the damaged section of the wire(s). This involves cutting out the bad section, splicing in a new piece of wire with connectors, and protecting the repair with heat shrink and anti-abrasion tape. GM specifies wire repair procedures in bulletin 10-00-89-005.
   Est. part cost: $5-$25
2. Shorted Chassis Harness Above Spare Tire 🔴 High Probability GM TSB #PIT5556A identifies a spot where the main chassis harness can rub against the frame cross-member above the spare tire. Body and frame flex during driving (especially under braking or on inclines) can cause the wires to chafe and short out, leading to intermittent issues.
   How to confirm: Lower the spare tire to gain access. Visually inspect the wiring harness that passes between the underbody and the frame for any signs of abrasion or damage. The issue may be intermittent and only appear when the body flexes.
   Typical fix: Repair the affected wires as needed. The TSB recommends reshaping the harness to be more oval and wrapping it with anti-abrasion tape to provide more clearance and prevent future damage.
   Est. part cost: $5-$25
3. Poor BCM Ground (G218) 🟡 Medium Probability According to GM TSB #PIT5405, the front dash insulator mat can get trapped between the Body Control Module (BCM) ground eyelet (G218) and the body stud. This creates a poor ground connection, causing a host of electrical issues and communication codes, including U0401.
   How to confirm: Locate ground G218 and inspect it to see if the insulator mat is caught under the eyelet. This can cause numerous seemingly unrelated electrical problems like the IPC or radio going blank.
   Typical fix: Remove the ground nut and eyelet. Cut away the section of the insulator mat that is interfering with the connection. Reinstall the ground eyelet and nut, ensuring a clean metal-to-metal contact. 🎬 Watch this walkthrough to properly fix the G218 ground.
   Est. part cost: $0-$5
4. Power Steering Control Module (PSCM) Software Error 🟡 Medium Probability GM TSB #20-NA-113 notes a calibration error in the PSCM on 2017-2018 models that can cause U0401 to remain as a 'current' code even if the original problem is gone. This can be misleading during diagnosis.
   How to confirm: This is difficult to confirm without a dealer-level scan tool. If wiring issues are ruled out and the code persists in the PSCM, a software issue is likely. The bulletin addresses a "Service Power Steering" message.
   Typical fix: The Power Steering Control Module (PSCM) needs to be reprogrammed with the latest software calibration by a GM dealership or a qualified shop with a J2534 programming tool. A stable voltage supply is critical during reprogramming.
   Est. part cost: $0
5. Faulty Sensor Input to ECM ⚪ Low Probability As noted in related GM bulletins like #17-NA-158, a fault in an unrelated sensor (like the Engine Coolant Temperature sensor) can cause the ECM to send invalid data over the network, triggering a U0401 in another module.
   How to confirm: Scan all vehicle modules for other trouble codes. If a code like P0128 (Coolant Thermostat Performance) is present alongside U0401, it is the likely root cause. Fixing the sensor-related code should be the first step.
   Typical fix: Diagnose and repair the other trouble code first. For example, fixing a P0128 might involve replacing the thermostat or coolant temperature sensor. Once fixed, the U0401 code can be cleared.
   Est. part cost: $30-$150

Rare But Worth Checking

• Faulty Engine Control Module (ECM): This is rarely the cause. Before replacing the ECM, all wiring, software, and sensor-related TSBs must be thoroughly investigated. ECM replacement is expensive and requires programming.
• Poor Battery Health or Low Voltage: Low system voltage can cause unpredictable behavior in control modules and trigger communication codes. Always ensure the battery and charging system are healthy before diving into complex network diagnostics. Check for loose or corroded battery terminals and ground connections throughout the vehicle.
• Aftermarket OBD-II Devices: Some aftermarket devices that plug into the OBD-II port, such as insurance trackers or Bluetooth performance monitors, can interfere with the CAN bus network and cause communication errors like U0401. One owner reported their "Service Stabilitrak" issue was resolved by unplugging a Bluetooth OBD-II adapter.

Diagnosis Steps

1. Perform a full vehicle scan to see which module(s) are setting the U0401 code and to check for any other DTCs. Note if the code is current or history.
2. Check battery voltage and charging system health. Ensure battery terminals are clean and tight. A weak battery can cause numerous communication faults.
3. If codes like P0128 are present, diagnose and fix that issue first.
4. Inspect BCM ground G218 for interference from the dash insulator mat, per TSB #PIT5405.
5. Following TSB #PIT5457C, remove the driver and passenger front sill plates and inspect the wiring harness (specifically Communication Enable circuit 5986) for any signs of chafing, corrosion, or broken wires.
6. Following TSB #PIT5556A, lower the spare tire and inspect the chassis harness where it passes over the frame for damage. This is a very common failure point.
7. If wiring is found to be damaged, repair it using appropriate splicing techniques and protect the harness from future damage with anti-abrasion tape.
8. If no wiring damage is found, especially on a 2017-2018 model, consult a dealer about TSB #20-NA-113 to check if the Power Steering Control Module requires a software update.
9. As a final step, if all else fails, diagnostics would move towards testing the CAN bus network integrity with an oscilloscope and considering a faulty ECM or other module.

Parts You'll Likely Need

• Wiring Repair Supplies — The most common cause is a damaged wire that needs to be spliced and repaired, not a component that needs to be replaced. This includes wire, butt connectors, heat shrink, and anti-abrasion tape.
  Trusted brands: 3M, Tesa
  Aftermarket price range: $5-$25
• Engine Control Module (ECM) (OEM #12663373) — This is a rare fix, only to be considered after all wiring and software issues are ruled out. Part number may vary by year and engine. Requires professional programming.
  Trusted brands: ACDelco
  OEM price range: $250-$450
  Aftermarket price range: $200-$350

Related Codes That Often Appear With This One

• U0121 — Lost Communication With Electronic Brake Control Module (EBCM). Often set together due to the same harness damage affecting multiple communication lines, as noted in TSB #PIT5457C.
• U0415 — Invalid Data Received From Electronic Brake Control Module (EBCM). Often set with U0401 when a wiring or module issue affects the whole network, as noted in TSB #PIT5457C.
• P0128 — Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). A faulty coolant temp reading can cause the ECM to send invalid data, triggering U0401 in the power steering module.
• U0073 — Control Module Communication Bus A Off. This code often appears with U0401 when there is a major disruption on the CAN bus, such as the harness shorting above the spare tire.

Technical Service Bulletins (TSBs) & Recalls

• PIT5457C: Addresses communication DTCs, including U0401, caused by damaged wiring under the sill plates.
• PIT5556A: Points to a shorted chassis harness above the spare tire causing multiple communication codes, including U0401.
• 20-NA-113 (replaces PIT5593B): Describes a PSCM calibration error that keeps U0401 as a current DTC, requiring a software update.
• 17-NA-158: Warns against replacing the power steering gear for U0401 when it's caused by another issue like a P0128 code.

Platform-Specific Known Issues

• A known issue of wiring chafing under the door sill plates is documented in TSB #PIT5457C, affecting the Communication Enable circuit (5986).
• A known issue of the chassis harness shorting to the frame above the spare tire is documented in TSB #PIT5556A. This can cause intermittent issues that are hard to trace as they depend on body flex.
• A software calibration issue in the Power Steering Control Module (PSCM) can cause a persistent U0401 on 2017-2018 models, addressed by TSB #20-NA-113.
• A poor ground connection at G218 due to an interfering dash insulator mat is a known cause of various communication codes, documented in TSB #PIT5405.

Mechanic-Grade Diagnostic Values

• High-Speed CAN Bus Network Resistance — expected: 60 Ohms. Failure: A reading of 120 Ohms indicates a missing termination resistor or an open in the bus. A reading near 0 Ohms indicates a short between CAN High and CAN Low wires. A reading of ~40-45 Ohms could indicate a third resistor on the network or a faulty module transceiver.
• Communication Enable Circuit 5986 Voltage — expected: Approximately 12 Volts (Battery Voltage). Failure: Low or no voltage when the ignition is on indicates an open, short, or high resistance in circuit 5986, which is a common cause of U0401 on this platform.
• CAN High Voltage to Ground — expected: 2.5V to 3.5V (Dominant state). Failure: Significant deviation from this range indicates a fault on the CAN High line.
• CAN Low Voltage to Ground — expected: 1.5V to 2.5V (Dominant state). Failure: Significant deviation from this range indicates a fault on the CAN Low line.

Hidden / Shadow Codes Worth Checking

• U0401:71: The ':71' is a symptom byte that means 'Invalid Data'. This indicates the receiving module (e.g., the Power Steering Control Module) got a signal from the ECM, but the data within that signal was flagged as invalid or illogical. It's a crucial clue that the problem is the *content* of the message, not a total loss of communication. (see via A professional-grade scan tool like the GM GDS2 (Global Diagnostic System 2) or a high-end aftermarket scanner is required to view symptom bytes.)

Scan Tool Commands That Help

• GDS2 / Techline Connect: Replace and Program Module — This function is used after physically replacing a control module, such as the Electronic Brake Control Module (EBCM). The new module must be programmed with the vehicle's VIN and correct software to communicate with other modules on the network.
• GDS2 / Techline Connect: Clear DTCs — After a programming event or repair, many 'lost communication' codes will be stored in various modules. This function clears all codes across the vehicle's networks.
• GDS2: Steering Wheel Angle Sensor Learn/Reset — If Stabilitrak or steering-related issues accompany the U0401 code, a steering angle sensor relearn may be necessary, especially after an alignment, software flash, or battery disconnect. This ensures the sensor's center position is correctly calibrated.

Wiring & Ground Locations

• G218 — Located on the body stud behind the dash, often interfered with by the dash insulator mat. Access typically requires removing the passenger or driver side kick panel and peeling back insulation.. This is a primary ground for the Body Control Module (BCM). A poor connection here can cause the BCM to malfunction, leading to a wide range of electrical and communication faults, including U0401.
• Circuit 5986 — This is the 'Communication Enable' circuit. It runs from the BCM to various modules, including the EBCM and PSCM. It is known to chafe and break under the driver's and passenger's front door sill plates.. This circuit acts as a 'wake-up' signal for many modules. If the signal is lost due to a wiring fault, modules won't communicate, leading to codes like U0121, or they may receive intermittent signals, contributing to U0401.
• EBCM Connector X1 — This is the main connector for the Electronic Brake Control Module (EBCM), which is part of the ABS pump assembly in the engine bay.. If diagnosing a U0401 set by the EBCM, this is the connector where you would test for voltage on Circuit 5986 and check for CAN bus signal integrity. A pinout diagram is required to identify the correct terminals.
• PSCM Connector — The connector at the Power Steering Control Module, which is part of the electronic power steering rack assembly.. This connector is a common point for corrosion and damage due to its location on the underbody. In one documented case, a pin rotted out of the connector, causing a loss of power steering and multiple communication codes.

Real Owner Repair Stories

• YouTube user comment on a diagnostic video (2018 GMC Sierra (platform mate)) — Constant "Service Stabilitrak" message, cruise control kicking off.
  ❌ Tried (didn't work) Driving the vehicle for months with the intermittent issue.
  ✅ What actually fixed it The owner discovered that a Bluetooth OBD-II adapter (for the Torque app) was plugged into the diagnostic port. As soon as the adapter was unplugged, the Stabilitrak warnings stopped and did not return. Plugging it into another truck immediately caused the same warning light to appear.

Model Year Variations Within This Range

• 2017-2018: A specific software calibration issue exists in the Power Steering Control Module (PSCM) that can cause U0401 to be stored as a current code even after the root cause is fixed. GM TSB #20-NA-113 addresses this by providing an updated software calibration that must be programmed by a dealer.