AutoCodes – GMC – U18A9 GMC

U18A9 GMC Code - Lost Communication With Transmission Range Control Module On Chassis Expansion CAN Bus

Quick Answer

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Transmission Range Control Module, Transmission Range Control Module harness is open or shorted, Transmission Range 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: U18A9 GMC indicates Lost Communication With Transmission Range Control Module On Chassis Expansion CAN Bus.
Common causes: Common causes include Faulty Transmission Range Control Module, Transmission Range Control Module harness is open or shorted, Transmission Range 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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 531

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 08, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code U18A9 GMC Description

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the devices. The devices 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 device as an availability indication of the transmitter device. Each message contains the identification number of the transmitter device. The Diagnostic Trouble Code (DTC) will set a supervised periodic message that includes the transmitter device availability that has not been received.

OBDII Code U18A9 GMC - Lost Communication With Transmission Range Control Module On Chassis Expansion CAN Bus - AutoCodes.com — U18A9 GMC Code - Lost Communication With Transmission Range Control Module On Chassis Expansion CAN Bus

What does this mean?

What are the Possible Causes of the DTC U18A9 GMC?

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

How to Fix the DTC U18A9 GMC?

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 U18A9 GMC 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 U18A9 GMC code?

Need more information on how to fix the U18A9 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U18A9 GMC code diagnosed by a professional: Find a repair shop in your area

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 U18A9 GMC Code

1. What are common symptoms of OBDII code U18A9 GMC?

Common symptoms include the transmission not shifting properly, the vehicle going into limp mode, and the Check Engine Light illuminating.

2. What can cause the OBDII code U18A9 GMC to appear?

This code is typically triggered by a communication error between the transmission range control module and the chassis expansion CAN bus.

3. How serious is the U18A9 GMC code?

This code can affect the proper functioning of the transmission, potentially leading to drivability issues. It is important to address this code promptly.

4. How should I diagnose the U18A9 GMC code?

Diagnosis involves using a professional OBDII scanner to check for codes, inspecting the transmission range control module, and testing the communication between modules.

5. Can I continue driving with the U18A9 GMC code present?

It is not recommended to continue driving with this code present, as it can lead to further damage to the transmission and other components.

6. How can I repair the U18A9 GMC code?

Repairing this code may involve checking and repairing any wiring or connector issues, replacing faulty modules, or reprogramming modules as needed.

7. Is it possible to reset the U18A9 GMC code without repairs?

Resetting the code without addressing the underlying issue may cause it to reappear. It is best to diagnose and repair the root cause of the problem.

8. Are there any common mistakes to avoid when dealing with the U18A9 GMC code?

Avoid overlooking simple wiring or connector problems, as these can often be the cause of communication errors triggering this code.

9. Can weather conditions affect the U18A9 GMC code?

Extreme weather conditions or water exposure can potentially cause communication issues between modules, leading to the U18A9 code appearing.

10. How can I prevent the U18A9 GMC code from recurring?

Regular maintenance, checking for loose connections, and addressing any transmission issues promptly can help prevent the U18A9 code from reappearing.