AutoCodes – GMC – U18AA GMC

U18AA GMC Code - Transmission Range Control Module Lost Communication With Engine Control Module

Quick Answer

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Engine Control Module (ECM), Engine Control Module harness is open or shorted, Engine 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: U18AA GMC indicates Transmission Range Control Module Lost Communication With Engine Control Module.
Common causes: Common causes include Faulty Engine Control Module (ECM), Engine Control Module harness is open or shorted, Engine 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 522

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 U18AA 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 U18AA GMC - Transmission Range Control Module Lost Communication With Engine Control Module - AutoCodes.com — U18AA GMC Code - Transmission Range Control Module Lost Communication With Engine Control Module

What does this mean?

What are the Possible Causes of the DTC U18AA GMC?

Faulty Engine Control Module (ECM)
Engine Control Module harness is open or shorted
Engine Control Module circuit poor electrical connection

How to Fix the DTC U18AA 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 U18AA 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 U18AA GMC code?

Need more information on how to fix the U18AA GMC 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 U18AA GMC Code

1. What are common symptoms of OBDII code U18AA in a GMC vehicle?

- Common symptoms include transmission shifting issues, engine stalling, loss of power, and illuminated warning lights on the dashboard.

2. What does the OBDII code U18AA indicate in a GMC vehicle?

- The code U18AA indicates a communication error between the Transmission Range Control Module (TRCM) and the Engine Control Module (ECM).

3. What are possible causes of the U18AA code in a GMC vehicle?

- Possible causes include faulty wiring or connectors, a malfunctioning TRCM or ECM, software glitches, or a loose connection between the modules.

4. How can I diagnose the U18AA code in my GMC vehicle?

- Diagnosing the U18AA code typically involves using a diagnostic scanner to retrieve the code, checking for related codes, inspecting wiring and connections, and performing communication tests between modules.

5. Can I still drive my GMC vehicle with the U18AA code present?

- It is not recommended to drive your vehicle with the U18AA code present, as it can lead to potential safety hazards and further damage to the transmission or engine components.

6. How can I repair the U18AA code in my GMC vehicle?

- Repair options may include fixing wiring or connector issues, replacing the TRCM or ECM if faulty, updating software, or reprogramming the modules to establish communication.

7. Can a DIY enthusiast fix the U18AA code issue in a GMC vehicle?

- While some basic troubleshooting steps can be done by DIY enthusiasts, resolving the U18AA code may require advanced diagnostic tools and expertise, making it advisable to seek professional help.

8. How much does it typically cost to repair the U18AA code in a GMC vehicle?

- Repair costs for the U18AA code can vary depending on the root cause of the issue, but it may range from a couple of hundred dollars for simpler fixes to over a thousand dollars for module replacements.

9. How long does it take to repair the U18AA code in a GMC vehicle?

- The repair time for the U18AA code can vary based on the complexity of the issue and the availability of parts. It may take a few hours to a full day for diagnosis and repair.

10. Are there any preventive measures to avoid the U18AA code in a GMC vehicle?

- Regular maintenance, such as checking and cleaning connectors, ensuring proper grounding, and keeping software updated, can help prevent issues leading to the U18AA code in your GMC vehicle.