AutoCodes – Generic – U2104

U2104 Code - Controller Area Network Bus Reset Counter Overrun

Quick Answer

Modules connected to the Controller Area Network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Control Module, Control Module harness is open or shorted, Control Module circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: U2104 indicates Controller Area Network Bus Reset Counter Overrun.
Common causes: Common causes include Faulty Control Module, Control Module harness is open or shorted, Control Module circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 3,266

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Feb 04, 2021

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U2104 Description

Modules connected to the Controller Area Network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. If no communication is detected on CAN serial data circuit, the Diagnostic Trouble Code (DTC) is set. A total non-communication condition may be caused by a short to battery or voltage on any of the CAN circuits or a short between the CAN high and low circuits.
The following modules communicate on CAN serial data bus: The Body Control Module (BCM), The Electronic Brake Control Module (EBCM), The Engine/Powertrain Control Module (ECM/PCM), and The Transmission Control Module (TCM).

OBDII Code U2104 - Controller Area Network Bus Reset Counter Overrun - AutoCodes.com — U2104 Code - Controller Area Network Bus Reset Counter Overrun

What does this mean?

What are the Possible Causes of the DTC U2104?

Faulty Control Module
Control Module harness is open or shorted
Control Module circuit poor electrical connection

How to Fix the DTC U2104?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the U2104 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the U2104 code?

Need more information on how to fix the U2104 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U2104 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U2104 Buick — Controller Area Network Bus Reset Counter Overrun
U2104 Cadillac — Controller Area Network Bus Reset Counter Overrun
U2104 Chevrolet — Controller Area Network Bus Reset Counter Overrun
U2104 GMC — Controller Area Network Bus Reset Counter Overrun
U2104 Pontiac — Controller Area Network Bus Reset Counter Overrun
U2104 Saturn — Controller Area Network Bus Reset Counter Overrun

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about U2104 Code

What does OBDII code U2104 mean?

Code U2104 indicates an issue where the Controller Area Network (CAN) bus reset counter has exceeded its allowable limit, often due to communication errors between modules.

What are the symptoms of code U2104?

Common symptoms include a check engine light, loss of communication with certain modules, erratic or non-functional electronic systems, and possibly the vehicle entering a limp mode.

What causes code U2104?

This code is typically caused by faulty wiring or connectors in the CAN bus network, interference in the communication signal, a failing control module, or software glitches.

Can a weak battery cause code U2104?

Yes, a weak or failing battery can cause voltage fluctuations that disrupt the CAN bus communication, potentially triggering the U2104 code.

How do you diagnose code U2104?

Diagnosis involves scanning for related codes, inspecting the CAN bus wiring and connectors for damage, testing module communication, and checking the battery and charging system.

Can you drive with code U2104?

While the vehicle may still be drivable, issues with communication between modules could affect safety-critical systems, so itâ€™s best to address the problem promptly.

How do you fix code U2104?

Repairs may include fixing or replacing damaged wiring or connectors, updating module software, reprogramming or replacing a faulty control module, or addressing power supply issues.

Is code U2104 specific to certain vehicle brands?

No, U2104 is a generic OBDII code, but the exact cause and repair steps may vary depending on the vehicle make and model.

Can a loose ground connection cause code U2104?

Yes, poor grounding can disrupt the CAN bus signal, leading to communication errors and triggering the U2104 code.

What tools are needed to troubleshoot code U2104?

Youâ€™ll need an OBDII scanner with CAN diagnostics, a multimeter for testing wiring and voltages, and possibly a factory service manual for the specific vehicle.