AutoCodes – Generic – U18AC

U18AC 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 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 1,330

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

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?

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 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 U18AC code?

Need more information on how to fix the U18AC code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U18AC code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U18AC Buick — Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus
U18AC Cadillac — Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus
U18AC Chevrolet — Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus
U18AC GMC — Transmission Range Control Module Lost Communication With Chassis Control Module On Chassis Expansion CAN Bus

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 Code

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

- Common symptoms include erratic shifting of the transmission, transmission slippage, and illumination of the Check Engine light.

2. What can cause the OBDII code U18AC to trigger?

- The code U18AC is triggered when the Transmission Range Control Module loses communication with the Chassis Control Module on the Chassis Expansion CAN Bus.

3. How serious is the U18AC code?

- The U18AC code should be addressed promptly as it can lead to potential transmission issues and affect the vehicle's performance.

4. How is the U18AC code diagnosed?

- Diagnosis involves using an OBDII scanner to retrieve the code, followed by checking the communication between the Transmission Range Control Module and the Chassis Control Module.

5. What are some possible repair options for OBDII code U18AC?

- Repair options include checking and repairing any damaged wiring or connectors between the affected modules, updating software, or replacing the faulty module.

6. Can I continue driving with the U18AC code present?

- It is not recommended to continue driving with the U18AC code present, as it can cause further damage to the transmission system.

7. How much does it typically cost to repair OBDII code U18AC?

- The cost of repairing the U18AC code can vary depending on the extent of the issue, but it may range from a few hundred to a few thousand dollars.

8. Can a DIY enthusiast fix the U18AC code at home?

- While some basic checks like inspecting wiring and connections can be done at home, diagnosing and repairing the U18AC code may require professional expertise and specialized tools.

9. Is the U18AC code specific to certain vehicle makes and models?

- The U18AC code can appear in various vehicle makes and models that are equipped with OBDII systems and CAN Bus communication networks.

10. How can I prevent the U18AC code from reoccurring in the future?

- Regular maintenance checks, ensuring proper electrical connections, and addressing any transmission issues promptly can help prevent the U18AC code from reoccurring.