AutoCodes – GMC – U18AC GMC

U18AC GMC Code - Transmission Range Control Module Lost Communication With Chassis 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 Chassis Control Module, Chassis Control Module harness is open or shorted, Chassis 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: U18AC GMC indicates Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus.
Common causes: Common causes include Faulty Chassis Control Module, Chassis Control Module harness is open or shorted, Chassis 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 653

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
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Code U18AC 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 U18AC GMC - Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus - AutoCodes.com — U18AC GMC Code - Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus

What does this mean?

What are the Possible Causes of the DTC U18AC GMC?

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

How to Fix the DTC U18AC 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 U18AC 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.

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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 U18AC GMC Code

1. What are the common symptoms of OBDII code U18AC GMC?

The common symptoms of code U18AC include transmission shifting issues, loss of communication between the transmission range control module and chassis control module, and the illumination of the check engine light.

2. What causes the OBDII code U18AC GMC to occur?

The code U18AC typically occurs due to a communication error between the transmission range control module and the chassis control module on the chassis expansion CAN bus. This can result from wiring issues, a faulty control module, or a malfunction in the CAN bus network.

3. How serious is the OBDII code U18AC GMC?

Code U18AC can affect the proper operation of the transmission system, leading to potential drivability issues. It is important to address this code promptly to ensure the vehicle functions correctly and to prevent further damage.

4. Can I continue driving with the OBDII code U18AC GMC active?

It is not recommended to continue driving with the U18AC code active, as it can impact the transmission's performance and overall drivability of the vehicle. It is best to address the issue as soon as possible.

5. How can I diagnose and repair the OBDII code U18AC GMC?

Diagnosing the U18AC code involves checking the wiring connections between the transmission range control module and chassis control module, testing the control modules for functionality, and inspecting the CAN bus network for faults. Repair may involve repairing or replacing damaged wiring, replacing faulty control modules, or addressing issues with the CAN bus network.

6. Are there any common DIY repair tips for fixing the OBDII code U18AC GMC?

While diagnosing and repairing code U18AC may require specialized tools and knowledge, some DIY enthusiasts may attempt to check the wiring connections, inspect for visible damage, and reset the codes using an OBDII scanner. However, for a thorough repair, it is recommended to seek professional help.

7. How much does it cost to fix the OBDII code U18AC GMC?

The cost of fixing the U18AC code can vary depending on the root cause of the issue. Repair costs may include labor charges for diagnosis and repair, the cost of replacement parts such as control modules or wiring harnesses, and any additional fees for reprogramming modules.

8. Can a low battery voltage trigger the OBDII code U18AC GMC?

Yes, a low battery voltage can potentially cause communication errors between control modules, including the transmission range control module and chassis control module. It is essential to ensure the vehicle's electrical system is in good condition to prevent such issues.

9. Will resetting the OBDII code U18AC GMC make it go away permanently?

Resetting the U18AC code may temporarily clear the fault code, but if the underlying issue causing the code is not addressed, it is likely to reappear. It is crucial to diagnose and repair the root cause of the problem to prevent the code from returning.

10. How long does it take to fix the OBDII code U18AC GMC?

The time required to fix the U18AC code can vary based on the complexity of the diagnosis and repair needed. Simple issues like loose connections may be resolved quickly, while more intricate problems such as faulty control modules or wiring harnesses may take longer to pinpoint and repair.