U0401 on 2015-2019 Chevrolet Silverado 2500: Causes, Symptoms, and Fixes

What's Unique About the 2015-2019 Chevrolet SILVERADO 2500

The GM K2XX platform, which includes the 2015-2019 Silverado 2500, is known for a specific wiring vulnerability. A Technical Service Bulletin (TSB #PIT5457D) identifies a common failure point in the wiring harness located under the driver and passenger sill plates. This harness contains the Communication Enable circuit (Circuit 5986), which is prone to damage from water intrusion and corrosion. This circuit is used by the Body Control Module (BCM) to 'wake up' other modules for communication. A fault here is the primary cause of U0401 on these trucks 🎬 Watch: Expert breakdown of U0401 causes and common fixes., making a wiring inspection in this specific area a top priority.

Diagnostic Flowchart

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

Symptoms You May Notice

• "Power Steering Assist Reduced" message on the driver information center (DIC).
• Service Stabilitrak warning light.
• Check Engine Light illuminated.
• ABS and Traction Control lights on.
• Sudden loss of power steering.
• Vehicle may enter "limp mode" with reduced engine power.
• A/C may be inoperative.
• Vehicle may have trouble starting.
• Intermittent cruise control dropout.

Most Likely Causes

1. Damaged or Corroded Wiring Harness Under Sill Plates 🔴 High Probability As documented in TSB #PIT5457D, the wiring harness routed under the driver and passenger sill plates is susceptible to moisture intrusion, physical damage, and corrosion. Specifically, the Communication Enable circuit (5986) and splice J365 are known weak points.
   How to confirm: Remove the driver and passenger sill plates and carefully peel back the carpet to visually inspect the wiring harness, especially the twisted pair CAN wires and Circuit 5986. Look for signs of corrosion (green or white powder), chafing, or broken wires. TSB #PIT5457D advises checking for ~12V on circuit 5986 at an affected module (like the EBCM) when the BCM is awake.
   Typical fix: Repair the damaged section of the harness by splicing in new wire using solder and adhesive-lined heat shrink tubing or OEM-approved splice connectors. Ensure the CAN bus wires maintain their original twist ratio to prevent interference. Protect the repair from future moisture damage.
   Est. part cost: $10-$50
2. Low or Unstable Battery Voltage 🟡 Medium Probability → Shop Vehicle Battery Modern control modules require stable voltage to operate correctly. A weak battery, failing alternator, or poor battery cable connections can cause modules to send corrupt data, triggering a U0401 code.
   How to confirm: Test the battery voltage with a multimeter with the engine off (should be ~12.4-12.6V) and while running (should be ~13.7-14.7V). Load test the battery to check its health. Check main ground connections for cleanliness and tightness.
   Typical fix: Recharge or replace the battery. Clean or replace corroded battery terminals. Replace the alternator if it's not charging correctly.
   Est. part cost: $150-$400
3. ECM/PSCM Software/Calibration Issue 🟡 Medium Probability GM has issued several bulletins for software issues. TSB #20-NA-111 notes a PSCM calibration error can cause U0401 to stay as a 'current' code even after a fix; the solution is reprogramming the PSCM. TSB #17-NA-158 links U0401 to an invalid coolant temp signal (P0128), advising to fix the P0128 issue first before suspecting the steering system.
   How to confirm: A GM dealer or a qualified shop with access to GM's service information system (TIS2WEB) can check for and apply any available software updates for the ECM and PSCM.
   Typical fix: Update the Engine Control Module (ECM) or Power Steering Control Module (PSCM) with the latest software calibration. This must be done by a dealer or a properly equipped independent shop.
   Est. part cost: $0 (parts), Labor cost varies
4. Faulty Engine Control Module (ECM) ⚪ Low Probability → Shop Engine Control Module (ECM) While less common than wiring or voltage issues, the ECM itself can fail internally, causing it to send invalid data to other modules on the network.
   How to confirm: This is typically a last resort after all other possibilities (wiring, power, grounds, software) have been exhaustively ruled out by a professional.
   Typical fix: Replace the Engine Control Module and program it to the vehicle. This requires specialized equipment.
   Est. part cost: $800-$1500

Rare But Worth Checking

• Failing Ignition Coil: In some cases, particularly when accompanied by a misfire code (e.g., P030X), a failing ignition coil can create enough electrical noise or voltage disruption to cause communication errors like U0401. One owner on Reddit reported fixing a U0401-71 by replacing a bad ignition coil on cylinder #6 after plugs and wires had no effect.
• Aftermarket OBD-II Devices: Some aftermarket devices left plugged into the OBD-II port, such as Bluetooth scanners or insurance monitoring dongles, can interfere with the CAN bus network. An owner of a 2018 Silverado traced a persistent Stabilitrak issue to his Bluetooth OBD-II adapter; unplugging it solved the problem.

Diagnosis Steps

1. Scan all vehicle modules for stored trouble codes. Note all codes and their status (current, history). Pay special attention to which module set the U0401 code.
2. Check battery health and charging system performance. Ensure voltage is stable and within specification (~12.6V engine off, 13.7-14.7V running).
3. Perform a thorough visual inspection of the wiring harness located under the driver and passenger side sill plates, as detailed in TSB #PIT5457D. Specifically look for corrosion or damage to the Communication Enable circuit (5986) and splice J365.
4. If a P0128 code is present with U0401, diagnose and repair the cause of the P0128 code first, as per TSB #17-NA-158.
5. Inspect the main ECM/PCM connectors and ground connections for tightness and corrosion.
6. If wiring and power sources are good, check for any available software updates for the ECM and PSCM, especially if codes are persistent, as noted in TSB #20-NA-111.
7. If the code persists after all other steps, advanced diagnostics on the CAN bus network with an oscilloscope may be needed to check for signal integrity.
8. As a final step, consider the possibility of a faulty ECM.

Parts You'll Likely Need

• Wiring Repair Supplies — The most common cause is a damaged wire (Circuit 5986) in the sill plate harness, requiring splicing and repair rather than a full component replacement.
  Trusted brands: 3M, ACDelco
  OEM price range: $10-$50
  Aftermarket price range: $5-$25
• Battery — A weak or failing battery can cause erratic voltage, leading to data corruption between modules.
  Trusted brands: ACDelco, DieHard, Optima
  OEM price range: $200-$350
  Aftermarket price range: $150-$250

Related Codes That Often Appear With This One

• U0077 — High Speed Communication Bus '–' Low. Often caused by the same wiring harness issue under the sill plates mentioned in TSB PIT5457D.
• U0121 — Lost Communication With Anti-Lock Brake System (ABS) Control Module. The EBCM is a common recipient of the invalid data, and this code often appears with U0401 due to the same root cause.
• U0131 — Lost Communication With Power Steering Control Module (PSCM). This code is frequently seen with U0401 when power steering is affected.
• U0415 — Invalid Data Received From Anti-Lock Brake System Control Module. This indicates a two-way communication problem on the network, often stemming from the same wiring fault.
• U0428 — Invalid Data Received From Steering Angle Sensor Module. Also listed in TSB PIT5457D as a related code due to the shared communication bus.
• P0128 — Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature. Per TSB #17-NA-158, an invalid coolant temp signal can cause the PSCM to set a U0401 code. The P0128 must be diagnosed and fixed first.

Technical Service Bulletins (TSBs) & Recalls

• PIT5457D: Service ABS / TCS / Power Steering and/or Suspension Message DTC U0077 U0121 U0126 U0131 U0139 U0151 U0401 U0415 U0428 (Circuit 5986)
• 17-NA-390: Power Steering Assist Reduced Displayed on Driver Information Center (DIC), Possible A/C Inoperative, Malfunction Indicator Lamp (MIL) Illuminated - DTCs P111E, U0401
• 20-NA-111: Service Power Steering Message Displayed, DTCs C0176, C0544, U0100, U0101, U0140, U0121, U0073, U0126, U0428 71, U0415, or U0401 Set in the PSCM
• 17-NA-158: Information on Steering Assist Reduced Displayed on Driver Information Center (DIC) - DTCs P0128 and U0401 Set

Platform-Specific Known Issues

• TSB #PIT5457D: Sill Plate Wiring Corrosion: This bulletin is the most critical piece of information for this code on this truck. It details a known issue where the Communication Enable circuit (5986) and related splices (like J365) corrode or break under the driver and passenger sill plates due to moisture. This single fault can trigger a cascade of communication codes, including U0401, and cause symptoms like loss of power steering and Stabilitrak warnings. The fix involves accessing the harness, finding the damaged section, and performing a durable, moisture-proof wire repair.

Mechanic-Grade Diagnostic Values

• High-Speed CAN Bus Network Resistance — expected: Approximately 60 Ohms. Failure: A reading of 120 Ohms indicates one of the two terminating resistors (often in the EBCM or another module) is not seen by the network. A reading significantly different from 60 or 120 Ohms (e.g., 40 Ohms or less) suggests a shorted wire or a faulty module.
• Communication Enable Circuit (5986) Voltage — expected: Approximately 11-12 Volts when the BCM is awake (e.g., ignition on).. Failure: Low or no voltage indicates an open, short, or high resistance in Circuit 5986, which is the primary issue described in TSB PIT5457D.
• Module Power Supply Voltage — expected: 12.4–12.8 V with less than 0.2 V ripple.. Failure: Unstable or low voltage can cause modules to malfunction and send invalid data.
• Module Ground Resistance — expected: Below 0.1 Ω.. Failure: High resistance indicates a poor ground connection, which can cause a variety of electrical and communication issues.

Hidden / Shadow Codes Worth Checking

• U0401-71: This symptom byte often indicates 'Invalid Data Received'. While the base U0401 code points to the general fault, the '-71' suffix is more specific. In the context of TSB #17-NA-158, it is set by the PSCM when it receives invalid data. It can also be triggered by low voltage conditions or electrical noise from other components. (see via A professional scan tool like the GM GDS2/Tech2 is required to view symptom bytes. Basic OBD-II readers will typically only show the base U0401 code.)

Scan Tool Commands That Help

• GDS2 / Techline Connect (TIS2WEB): PSCM Reprogramming — Use this function when a U0401 code remains 'current' in the Power Steering Control Module (PSCM) even after a potential root cause has been fixed and codes have been cleared. TSB #20-NA-111 identifies a calibration error where the PSCM fails to move the DTC to 'history'. Reprogramming the PSCM with the latest software is the specified fix.
• GDS2: Functional Tests / Output Controls — To isolate whether a module is responding. For example, a technician can use GDS2 to command the ABS compressor on to verify the EBCM is functional, even if it's setting communication codes. This helps differentiate between a faulty module and a wiring/network problem.

Wiring & Ground Locations

• Splice J365 — Located in the wiring harness under the passenger front sill plate.. TSB #PIT5457D specifically calls out this splice as a known area where the Communication Enable Circuit (5986) can develop high resistance or an open, leading to U0401 and other communication DTCs.
• Sill Plate Harness — The main chassis harness runs under both the driver and passenger side door sill trim plates.. This is the primary location for chafing, corrosion, and damage to Circuit 5986 due to water intrusion and foot traffic. Inspection and repair in this area are the most common fix for U0401 on this platform.
• G103 — On the front of the passenger side cylinder head.. This is a major engine ground point. A loose or corroded connection here can cause unstable voltage and electrical noise, disrupting module communication and potentially triggering a U0401 code.
• EBCM Connector (X1) — At the Electronic Brake Control Module, typically located on the driver's side frame rail.. This is a key point for testing. The High-Speed GMLAN bus wires are on pins 26 and 27 (Tan/Black). The Communication Enable circuit (5986) can be tested at its pin on this connector to verify it's receiving the wake-up signal from the BCM.

Real Owner Repair Stories

• Reddit user Sorry-Conclusion1658 (2015 Silverado (engine not specified, but another user had the same issue on a 5.3L)) — Engine misfire and code U0401-71.
  ❌ Tried (didn't work) Replacing all spark plugs., Replacing all spark plug wires.
  ✅ What actually fixed it Replacing the ignition coil on the misfiring cylinder (#6). The electrical noise or voltage disruption from the failing coil was causing the communication error code.

Model Year Variations Within This Range

• 2017-2019: The L5P Duramax diesel engine was introduced, replacing the LML from 2015-2016. This involved a completely different fuel system (Denso HP4 pump instead of Bosch CP4) and engine controls. While the U0401 CAN bus issue is often chassis-related (sill plate wiring) and affects all engines, diagnostics involving the ECM are specific to the engine type.
• 2015-2017: Early models with the 8L90 8-speed automatic transmission were prone to a significant torque converter clutch shudder, addressed by TSB 18-NA-355 which specified a fluid flush with a newer type of fluid. While not directly causing U0401, severe driveline issues can sometimes introduce electrical noise or place unexpected loads on control modules.