Fix U0001: Mechanic’s solutions that WORKED

The U0001: High Speed CAN Communication Bus fault code, which relates to issues within the CAN C bus circuit, is a concern that car owners should take seriously. While it may not immediately lead to a breakdown, it can disrupt communication between vital vehicle systems, potentially affecting various functions.

U0001 quick overview

Meaning	U0001: High Speed CAN Communication Bus
Is it serious?	It is potentially serious as it indicates a communication fault within the vehicle’s network. It may affect the functionality of various vehicle systems and should be addressed.
Possible causes	– Faulty or damaged CAN C bus wiring – Problems with modules connected to the CAN C bus – Issues with the TIPM (Totally Integrated Power Module)
How to diagnose?	Check CAN Bus Wiring: Inspect the wiring of the CAN C bus for damage, loose connections, or shorts to ground. Test Modules: Test the modules connected to the CAN C bus to ensure they are functioning correctly and communicating with the bus. Verify TIPM Operation: Evaluate the operation of the TIPM, which acts as a gateway for the CAN C bus. Consider replacement if necessary. Use Diagnostic Tools: Utilize diagnostic tools to read and clear fault codes, monitor communication on the CAN C bus, and identify specific issues.

How to fix U0001 – learn from mechanics

I looked into U0001 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: Volvo

Vehicle Information: 2007 Volvo S40 2.4i 2.4L

Issue + Repair History: After replacing the battery, the check engine light remained on with codes P0600 and U0001. No additional repair history mentioned.

Other OBD2 Codes + Test Results: P0600 – Serial Communication Link Malfunction U0001 – High-Speed CAN Communication Bus Performance

Suggestions to Fix Issue: Check fuses related to the codes, as low voltage can cause blown fuses. Inspect connectors around the front of the transmission under the air filter box for corrosion. Use an OE scan tool for proper communication with the Volvo, as some aftermarket tools may not work correctly.

Final Fix: The issue was resolved by clearing the codes and starting the engine, driving for 42 miles without the P0600 code reappearing. This fix suggests that the problem may have been related to communication issues that were resolved through this procedure.

Case #2: Jeep

Vehicle Information: 2016 Jeep Cherokee Limited 3.2L

Issue + Repair History: The vehicle was involved in a light front collision before coming to the shop. The check engine light was on with DTC C10D0 indicating a parking brake failure, despite the parking brake working correctly. Additionally, there was DTC U0001 in the parking brake module (PBM), indicating a CAN C Bus communication issue. The radiator fan harness had been repaired after the collision.

Other OBD2 Codes + Test Results: DTC C10D0 in the PCM (Powertrain Control Module) DTC U0001 in the TCM (Transmission Control Module) and PBM (Parking Brake Module)

Suggestions to Fix Issue:

1. Begin diagnosis by referencing the wiring diagram.
2. Check the ground location G923A behind the left rear inner quarter panel trim. Disassemble, clean, and reassemble this ground location, ensuring there is no paint coating interfering with the ground connection.
3. Remove paint from the stud and contact location to reveal metal.
4. After cleaning the ground (G923A), re-test for normal operation.
5. Consider using a Chrysler subscription for code clearing, as the scanner may not have been able to clear the codes.

Final Fix: The issue was resolved after fixing wiring problems. However, the codes could only be cleared using a Chrysler subscription, indicating that the scanner used initially couldn’t clear the codes.

Case #3: Kia

Vehicle Information: 2005 Kia Spectra EX 2.0L

Issue + Repair History: The car initially came in with a check engine light indicating a bad catalytic converter (cat). After clearing the code to reset monitors for a state inspection, the car became stuck in first gear, and a code U0001 could not be cleared.

Other OBD2 Codes + Test Results: U0001 – Loss of communication

Suggestions to Fix Issue:

1. Check the connectors, especially the transmission connector, to ensure they are properly plugged in.
2. Verify if the catalytic converter replaced was an OEM-style cat.
3. Ensure that there is data communication with the transmission module, as a loss of communication can lead to such issues.

Final Fix: The problem was due to the customer jump-starting the car before it came to the shop, which fried the PCM (Powertrain Control Module). Installing a new computer resolved the issue, and the car returned to normal operation.

Case #4: Pontiac

Vehicle Information: 2009 Pontiac G3 Wave 1.6L

Issue + Repair History: The car had the following issues:

• Intermittent speedometer cut out.
• Periodic cluster failure, requiring a 10-minute wait before the car would start and the speedometer issue would return.
• DTC U0001 stored in TCM (Transmission Control Module).

Other OBD2 Codes + Test Results:

• P0700 – Transmission requests MIL On
• U0001 – In TCM – High-Speed CAN Communication Bus error

Suggestions to Fix Issue:

1. Check for signal at connector X2 pin 5 (dark green and white wire) at the cluster.
2. Verify if the car has a remote start wired into the data line or an aftermarket radio with an interface, as they could cause data line problems.
3. Remove the OnStar fuse (with the ignition off and powered down) and recheck operation.
4. Check for a bad ground or a break in the wiring.
5. Run a jumper wire to see if the issue persists, which would indicate a bad wire.
6. Check and clean all ground connections.
7. Isolate modules that show a drop in communication and check their power and ground.
8. Consider the possibility of the radio causing issues, as GM radios can affect the speed signal. Try unhooking the radio for test purposes.

Final Fix: The issue was traced to the VCIM (Vehicle Communication Interface Module), which contains the OnStar module. It was pulling the CAN bus down for the speedometer. The fix involved bypassing the VCIM by jumping the purple and yellow wires from each connector. This resolved the sporadic speedometer issue and eliminated the parasitic draw caused by the VCIM. The dash did not experience any further failures after this fix.

Case #5: Dodge

Vehicle Information: 2008 Dodge Charger SE 2.7L

Issue + Repair History: The car had the following issues:

• No crank.
• No communication with most modules.
• No ABS, no cruise control.
• Limited functionality due to being a base model.
• U0001 CAN C Bus – active.
• Approximately 2.39V on CAN C Bus WT/LB and 2.59 on CAN C Bus WT/BK at every module.
• Approximately 63 ohms resistance and no shorts to ground.
• Wireless Control NOID visible through the instrument cluster.
• Crank sensor harness had a meltdown and was repaired.
• No computer control at the starter relay, although all powers were present.

Other OBD2 Codes + Test Results:

• U0001 – CAN C Bus Active

Suggestions to Fix Issue:

1. Check all CAN C bus wires for voltage (2.39/2.49 volts) and resistance (close to 63 ohms).
2. Verify which module wakes up the PCM (Powertrain Control Module) and check its operation.
3. Use a high-speed lab scope to analyze the CAN packet data, as voltage measurements may not suffice.
4. Inspect the Steering Column Control Module connector for spread or damaged terminals and repair as needed.
5. Try grounding the battery to the engine block with jumper cables to test for a ground issue.
6. Scope the CAN-C bus to check the signal and confirm communication between modules.
7. Consider the possibility of a faulty TIPM (Totally Integrated Power Module), which serves as the “gateway” between CAN-B and CAN-C.

Final Fix: The issue was resolved by replacing the Gateway (TIPM). Scoping the CAN C bus had shown a good pattern at all modules, and the TIPM was one of the few modules that could communicate. Replacing the TIPM solved the no crank and no communication issues, allowing the car to start and communicate with the necessary modules.

Advice	Diagnostic Step
Check CAN C bus voltage and resistance	Measure voltage and ensure proper resistance on CAN C bus wires.
Verify which module wakes up the PCM	Identify the module responsible for waking up the PCM and check its operation.
Use a high-speed lab scope for CAN data	Utilize a high-speed lab scope to analyze CAN packet data for communication issues.
Inspect connectors for damage	Check connectors for spread or damaged terminals and repair as needed.
Consider TIPM replacement	Evaluate the possibility of a faulty TIPM (Totally Integrated Power Module) and consider replacement.