AutoCodes – Hummer – U0121 Hummer

U0121 Hummer Code - Lost Communication With Electronic Brake Control Module

Quick Answer

Modules connected to the high speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Electronic Brake Control Module (EBCM), EBCM harness is open or shorted, EBCM 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: U0121 Hummer indicates Lost Communication With Electronic Brake Control Module.
Common causes: Common causes include Faulty Electronic Brake Control Module (EBCM), EBCM harness is open or shorted, EBCM 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 3,650

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 Jun 29, 2020

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code U0121 Hummer Description

Modules connected to the high speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module. The Diagnostic Trouble Code (DTC) sets when a periodic message from the Electronic Brake Control Module (EBCM) has not been received.

OBDII Code U0121 Hummer - Lost Communication With Electronic Brake Control Module - AutoCodes.com — U0121 Hummer Code - Lost Communication With Electronic Brake Control Module

What does this mean?

What are the Possible Causes of the DTC U0121 Hummer?

Faulty Electronic Brake Control Module (EBCM)
EBCM harness is open or shorted
EBCM circuit poor electrical connection

How to Fix the DTC U0121 Hummer?

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 does this mean?

Code Tech Notes

There is a factory service bulletin for the 2008-2009 HUMMER H2:
2008-2009 HUMMER H2 Factory Service Bulletin OBDII Code U0121

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the U0121 Hummer 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 U0121 Hummer code?

Need more information on how to fix the U0121 Hummer code? Get Access to Factory Service Manuals

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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 U0121 Hummer Code

1. What are the common symptoms of OBDII code U0121 in a Hummer vehicle?

The common symptoms of code U0121 in a Hummer include the ABS warning light coming on, loss of communication with the Electronic Brake Control Module (EBCM), and potential issues with the vehicle's braking system.

2. What are the possible causes of code U0121 in a Hummer?

Possible causes of code U0121 in a Hummer include damaged wiring or connectors, a faulty Electronic Brake Control Module, a weak or dead battery, or issues with the CAN bus communication system.

3. How can I diagnose the cause of code U0121 in my Hummer?

Diagnosing code U0121 in a Hummer involves conducting a thorough inspection of the wiring and connectors related to the Electronic Brake Control Module, checking the battery voltage, and using a diagnostic scanner to retrieve additional fault codes and data.

4. Can I still drive my Hummer with code U0121 present?

It is not recommended to drive your Hummer with code U0121 present, as it indicates a communication issue with the Electronic Brake Control Module that could affect the vehicle's braking system and overall safety.

5. How can I repair OBDII code U0121 in my Hummer?

To repair code U0121 in a Hummer, you may need to repair or replace damaged wiring or connectors, replace the Electronic Brake Control Module if necessary, ensure the battery is in good condition, and clear the fault codes using a diagnostic scanner.

6. Is it possible to reset OBDII code U0121 in a Hummer without fixing the underlying issue?

Resetting code U0121 without addressing the underlying issue, such as a communication problem with the Electronic Brake Control Module, may temporarily clear the code but will likely result in it reoccurring once the problem persists.

7. Can a DIY enthusiast fix OBDII code U0121 in a Hummer?

Depending on their skill level and access to tools, a DIY enthusiast may be able to fix code U0121 in a Hummer by inspecting wiring and connectors, replacing parts as needed, and using a diagnostic scanner to clear fault codes.

8. How much does it cost to repair OBDII code U0121 in a Hummer at a repair shop?

The cost to repair code U0121 in a Hummer at a repair shop can vary depending on the exact cause of the issue, the cost of parts and labor, and the shop's hourly rate. It is recommended to obtain quotes from multiple shops for comparison.

9. Will resetting the vehicle's computer clear OBDII code U0121 in a Hummer?

Resetting the vehicle's computer may temporarily clear code U0121, but if the underlying issue causing the communication problem with the Electronic Brake Control Module is not addressed, the code is likely to return.

10. How urgent is it to address OBDII code U0121 in a Hummer?

It is important to address code U0121 in a Hummer promptly, as it indicates a communication problem with the Electronic Brake Control Module that could impact the vehicle's braking system and overall safety.