Fix U0140: Mechanic’s solutions that WORKED

The code U0140: Lost Communication With Body Control Module indicates a failure in communication between the vehicle’s primary computer systems and the Body Control Module (BCM). This code typically suggests issues within the vehicle’s network, affecting essential features like lighting, door locks, and various comfort controls.

U0140 quick overview

Meaning	U0140: Lost Communication With Body Control Module
Is it serious?	Yes, as it can affect crucial vehicle functions and safety systems.
Possible causes	– Damaged or worn wiring harnesses – Faulty or improperly programmed BCM – Corrosion or poor connections in module connectors – Aftermarket installations interfering with electrical systems – Open or shorted CAN bus circuits – Grounding issues
How to diagnose?	Inspect BCM and Connections: Check the BCM for programming, damage, and secure connections. Examine Wiring: Look for damage or wear in the wiring, especially in known trouble areas. Measure CAN Bus Resistance: Test resistance between DLC pins (typically 6 and 14) for network issues. Verify Module Communications: Use diagnostic tools to check communication with the BCM, ECM, TCM, etc. Check for Aftermarket Additions: Inspect any aftermarket installations for potential interference. Review Service Bulletins: Look into manufacturer’s bulletins for common issues related to the specific vehicle model.

In simple terms, the U0140 code means that your car’s computer can’t talk to one of its important parts, the Body Control Module. This module helps manage things like your car’s lights, locks, and interior features. If this code appears, it’s like a part of your car’s “language” has been lost, and it needs to be fixed to ensure everything works smoothly and safely.

How to fix U0140 – learn from mechanics

I looked into U0140 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Chevrolet

Vehicle Information

• 2007 Chevrolet Equinox LT 3.4L Computer

Issue + Repair History

• Intermittent activation of stabilitrak and traction control lights
• Power steering loss, door locks cycling, lights going out briefly
• Previous repair attempts: Reprogramming EBCM and PSCM
• Fault Codes: P0131, P0140, U0131, U0140

Other OBD2 Codes + Test Results

• Not mentioned

Suggested Fixes

• Replace and reprogram the Body Control Module (BCM)
• Check and ensure all BCM ground circuits are secure
• Inspect for potential short circuits in the BCM harness
• Check alternator output (voltage, amperage, resistance) under load

Final Fix

• Replaced and programmed a new BCM
• Addressed a potential cause: corroded and loose main body ground from the battery

Case #2: Dodge

Vehicle Information

• 2011 Dodge Charger SE 5.7L

Issue + Repair History

• TPMS flashing, ABS and TCS issues, loss of steering assist, red steering wheel light flashing
• Replaced Steering Column Control Module, problem persisted

Other OBD2 Codes + Test Results

• Numerous fault codes: U0100, U0126, U0002-88, U0200-00, U0199-00, U0212-00, U0121-00, U0011-00, U0002-00, U0212-00, U0140, U0002-00, B222c-000, U0140-00, B210a-16

Suggested Fixes

• Conduct a loss of communication test with Witech to identify problematic modules
• Disconnect modules one by one to see if bus communication improves
• Check square wave signal on bus for shorting or opening
• Utilize Witech’s “loss of comm test” to get detailed insights on module communications

Final Fix

• Replaced the Electronic Steering Module Assembly, resolving the issue

Case #3: Buick

Vehicle Information

• 2006 Buick Lucerne CX 3.8L

Issue + Repair History

• No R6 relay action, no cranking, no shifter position indicator
• Fault Code: U0140
• Checked: BCM, ignition switch, ECM, under-hood fuse box, all fuses, wire harness
• Replaced and programmed BCM and ECM
• Tested CAN system resistance (62 ohms, normal)
• Engaged starter with remote switch and by grounding R3 relay control side

Other OBD2 Codes + Test Results

• Not mentioned

Suggested Fixes

• Check if U0140 code is in all modules or specific ones
• Verify communication with BCM, ECM, TCM
• Inspect ignition switch power and ground paths through BCM to the fuse box
• Disconnect and jumper CAN lines on EBCM to check PRNDL display restoration
• Examine power and ground to R6 relay coil

Final Fix

• Identified a poor wire and a bad BCM
• Addressed issue by not copying old BCM to new BCM
• Specifically, repaired a damaged wire (details of wire not specified)

Case #4: Mazda

Vehicle Information

• 2010 Mazda 3 i 2.0L

Issue + Repair History

• ABS and steering indicators lit on the dashboard
• Power steering functional, ABS not working
• Fault Code: U0140 in ABS and power steering module
• Actions taken: Replaced ABS module, BCM (and programmed), swapped steering module with a known good one
• Tested CAN low and high wires, scope checked CAN lines at steering, ABS module, and BCM

Other OBD2 Codes + Test Results

• Pin 6 / 14 DLC – 65 ohms

Suggested Fixes

• Steering Angle Sensor issues can corrupt CAN communication
• Isolate and test the module in question
• Check the resistance in the circuit, as 65 ohms might indicate an issue
• Verify BCM CAN communication, check for additional sub-codes indicating specific symptoms

Final Fix

• Discovered the wrong clockspring (steering angle sensor unplugged)
• Replaced clockspring with the correct part, resolving the issue

Case #5: GMC

Vehicle Information

• 2011 GMC Sierra 1500 SLE 5.3L

Issue + Repair History

• Intermittent warning lights, speedometer issues, occasional no-start
• No communication with PCM or ABS during no-start incidents
• Suspected failing module or wiring short in the bus circuit
• Resistance between pins 6 and 14 on DLC varies (120 ohms normally, lower when malfunctioning)

Other OBD2 Codes + Test Results

• Fault Codes: U0073, U0101, U0102, U0109, U0121, U0140

Suggested Fixes

• Check for wiring issues, especially for intermittent bus line problems
• Look for aftermarket additions or terminal fretting issues
• Examine common areas for chafed, damaged, or shorted wiring
• Test resistance in the data lines, check for open or shorted circuits
• Inspect BCM and TCM connections, consider voltage drop on negative battery cable

Final Fix

• Found wiring at the driver’s side of the engine front cover with VREF circuit had rubbed through on a transmission cooler line crimp fitting
• Repaired wiring, which resolved the issue
• Reviewed service bulletins for common wiring trouble spots on similar vehicles

Common Advice for U0140 Fault Code	Diagnostic Step Description
Check BCM (Body Control Module) and connections	Inspect for any issues with the BCM including proper programming, connections, and potential damage.
Inspect wiring harnesses for damage or wear	Examine wiring, especially in areas prone to wear or rubbing, for any signs of damage, chafing, or exposure.
Test CAN bus system resistance	Measure resistance between specific CAN bus pins (often 6 and 14 on the DLC) to ensure proper network integrity.
Evaluate module communications	Use diagnostic tools to confirm communication with various vehicle modules like ECM, TCM, and BCM.
Look for aftermarket installations or modifications	Aftermarket additions can sometimes interfere with vehicle’s electrical systems and should be inspected.
Consider related service bulletins for common issues	Review manufacturer’s service bulletins for known issues and advice specific to the vehicle model.