Fix U0073: Mechanic’s solutions that WORKED

The code U0073: Control Module Communication Bus “A” Off signals a disruption in the Control Module Communication Bus “A,” indicating a breakdown in the vehicle’s internal communication network. This issue is most commonly caused by problems in the Controller Area Network (CAN) bus system, such as faulty control modules, damaged wiring, or interference from aftermarket installations.

U0073 quick overview

Meaning	U0073: Control Module Communication Bus “A” Off.
Is it serious?	Yes, it can affect the vehicle’s communication network, leading to various system malfunctions.
Possible causes	– Faulty or failing control module (such as ECM, TCM, or ABS) – Damaged or corroded wiring and connectors in the CAN bus system – Faulty sensors or actuators connected to the CAN bus – Problems with the vehicle’s power supply or ground connections – Aftermarket installations or modifications interfering with the CAN bus
How to diagnose?	Inspect Wiring and Connectors: Check for damage or corrosion in the wiring and connectors of the CAN bus system. Check Individual Modules: Isolate and test modules like ECM, TCM, or ABS for faults. Scan for Additional Codes: Look for other diagnostic trouble codes that could indicate related issues. Verify Power and Grounds: Ensure all power and ground connections to the modules are secure and functional. Utilize an Oscilloscope: Scope the CAN bus signals for irregularities in the communication patterns. Consider Aftermarket Additions: Check for any aftermarket installations that could be interfering with the CAN bus.

This error code means there’s a problem with the main system that allows different parts of your car to talk to each other. It’s like the car’s internal phone line is down. This can lead to various issues in the car since the parts can’t communicate properly, making it important to address.

How to fix U0073 – learn from mechanics

I looked into U0073 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: Mazda

Vehicle Information

• 2003 Mazda 6 i, 2.3L

Issue + Repair History

• Poor Idle Quality, Cuts out, Stall, MIL Lamp on
• Initial Code: P2101 (TAC Motor Circuit Range/Performance)
• Additional Codes: U0073 (Control Module Communication Bus Off), U0100 (Lost Communication with ECM/PCM A)

Other OBD2 Codes + Test Results

• Voltage at PCM terminal 3M: 1.1 volts
• Voltage at PCM terminal 3J: 0.25 to 0.75 volts

Suggestions to Fix Issue

• Perform wiring test from throttle body to PCM
• Clear code and test drive
• Check dealer for reflash related to false U codes
• Consider throttle body replacement
• Address P codes primarily if U codes have been reflashed

Final Fix

• Bad throttle body identified as the primary issue
• Cleared U codes after confirming reflash was done for them
• Replaced the throttle body to resolve P2101 code

Case #2: Ford

Vehicle Information

• 2006 Ford Mustang, 4.0L

Issue + Repair History

• ABS Light on when going over 10km/h
• Codes: U-0073 (Control Module Communication Bus A OFF), U-2011 (Unknown)
• Related Repair History: Crash damage

Other OBD2 Codes + Test Results

• Scan codes: U-0073, U-2011

Suggestions to Fix Issue

• Check and verify grounds and power supplies
• Inspect wiring in crash repair area for shorts or breaks
• Consider wheel speed sensor, especially in the crash-affected area
• Check ABS wheel ring clearance
• ABS module communicates on the CAN bus; check for damage to connector or harness
• Inspect ABS module connector C135 for damage

Final Fix

• Clearing body-related codes and re-road testing cleared U-0073 code
• ABS and traction control lights stayed off after Ford re-scan
• Low battery voltage code during second road test may have contributed to communication problems

Case #3: Suzuki

Vehicle Information

• 2007 Suzuki SX4, 2.0L

Issue + Repair History

• ABS/Brake light flashing
• Auto AWD light on
• Check engine light on
• Codes: C1250, U0073, U0101, B1315
• No communication with ECM or TCM

Other OBD2 Codes + Test Results

• C1250: Coupling air temperature sensor open
• U0073: Control Module Communication Bus Off
• U0101: Lost Communication With TCM
• B1315: OCM operating temperature out of range

Suggestions to Fix Issue

• Check wiring diagrams and chase out CAN bus faults
• Investigate any aftermarket security systems or radios
• Check all fuses, power, and grounds
• Consider disconnecting the battery for an adaptive reset
• Disconnect modules to see if one is causing the bus to be pulled too low

Final Fix

• Found red pin 52 wire chaffed through and grounded out between ECM & TCM
• Repairing the wire resolved the communication issues

Case #4: Chevrolet

Vehicle Information

• 2012 Chevrolet Silverado 1500 LT, 5.3L

Issue + Repair History

• Poor Idle Quality, Cuts out, MIL Lamp on
• Codes: P1516 (Throttle Body Performance), P2101 (Throttle Body Performance), U0073 (CAN Bus High)
• Actions Taken: Replaced throttle body and pedal assembly, tested wiring and PCM, repaired damaged wiring under carpet

Other OBD2 Codes + Test Results

• Voltage drop wiring test: Good

Suggestions to Fix Issue

• Verify ground and power at throttle body
• Check left side valve cover harness loom for damage
• Check 5V reference and harness to crankshaft position sensor
• Scope CAN network for proper voltage level
• Disconnect modules one by one to isolate communication issue
• Perform throttle relearn procedure
• Consider the possibility of a bad PCM

Final Fix

• Replacing the PCM resolved the issues
• Performed throttle body relearn after PCM replacement

Case #5: Ford

Vehicle Information

• 2005 Ford Crown Victoria, 4.6L

Issue + Repair History

• ABS light and traction control light on, then go off after 2-3 minutes
• Codes: U0073 (No CAN communication), U1900
• “Layover” harness installed by dealer
• VAPS Module and ABS Module replaced at dealership

Other OBD2 Codes + Test Results

• Code U0073 detected with Ford WDS system

Suggestions to Fix Issue

• Check ABS pump for loss of pressure
• Proper repair of CAN wires; should be shielded or twisted pair, same gauge as original
• Consider solder and heat shrink for connections
• Check wiring harness running from battery junction box for damage

Final Fix

• Removed dealer-made “harness”
• Twisted wires tightly together, soldered connections at the controller and bulkhead
• After repair, ABS light did not come on and all diagnostics passed

Common Advice	Diagnostic Step Description
Check and Repair Wiring	Inspect and repair any damaged, chafed, or corroded wiring, especially in areas prone to wear or where damage is likely.
Use OEM Parts for Replacements	When replacing parts, especially sensors and modules, use original equipment manufacturer parts for compatibility and reliability.
Test Power and Ground Connections	Verify that all power and ground connections are secure and functioning correctly.
Scope CAN Network	Use an oscilloscope to check the CAN network for proper voltage level and signal integrity.
Disconnect Modules to Isolate Issue	Disconnect modules one by one to find if one is causing the bus to be pulled too low or causing communication issues.
Solder Connections for Reliability	For wire repairs, use solder and heat shrink instead of butt connectors for more reliable connections.
Check for Proper Wire Gauge and Shielding	Ensure repaired or replaced wires match the original gauge and are properly shielded if required.
Perform System Relearn Procedures	After repairs or part replacements, perform any necessary system relearn procedures with a suitable scan tool.