AutoCodes – Generic – U18A1

U18A1 Code - Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus

Quick Answer

Devices connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Coolant Temperature Control Module, Coolant Temperature Control Module harness is open or shorted, Coolant Temperature 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: U18A1 indicates Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus.
Common causes: Common causes include Faulty Coolant Temperature Control Module, Coolant Temperature Control Module harness is open or shorted, Coolant Temperature 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 2,504

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 U18A1 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 U18A1 - Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus - AutoCodes.com — U18A1 Code - Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus

What does this mean?

What are the Possible Causes of the DTC U18A1?

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

How to Fix the DTC U18A1?

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 U18A1 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 U18A1 code?

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Information for Specific Makes

U18A1 Buick — Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus
U18A1 Cadillac — Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus
U18A1 Chevrolet — Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management CAN Bus
U18A1 GMC — Lost Communication With Coolant Temperature Control Module On High Voltage Energy Management 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 U18A1 Code

1. What are common symptoms of OBDII code U18A1?

- Common symptoms include issues with coolant temperature control, engine overheating, poor fuel efficiency, and possibly the vehicle going into a reduced power mode.

2. What can cause the OBDII code U18A1 to set?

- The code can be set due to a communication breakdown between the engine control module and the coolant temperature control module on the high voltage energy management CAN bus.

3. How can I diagnose the U18A1 code?

- Diagnosis involves checking the wiring and connectors between the engine control module and the coolant temperature control module, as well as ensuring proper power and ground connections.

4. What repairs are typically needed for the U18A1 code?

- Repairs may involve repairing or replacing damaged wiring or connectors, resetting the fault codes, and ensuring proper communication between the modules on the CAN bus.

5. Can a faulty coolant temperature control module cause the U18A1 code?

- Yes, a faulty coolant temperature control module can cause the code to set if it is not communicating properly with the engine control module.

6. Is it safe to drive with the U18A1 code present?

- It is not recommended to drive with the U18A1 code present, as it can lead to engine overheating and other potential issues that may affect the vehicle's performance.

7. How do I reset the U18A1 code after making repairs?

- After making necessary repairs, the code can be reset using an OBDII scanner or by disconnecting the vehicle's battery for a few minutes to clear the fault code.

8. Can a low battery voltage cause the U18A1 code to set?

- Yes, low battery voltage or poor ground connections can sometimes lead to communication issues between modules and trigger the U18A1 fault code.

9. Will the U18A1 code cause the check engine light to illuminate?

- Yes, the U18A1 fault code will trigger the check engine light to illuminate on the vehicle's dashboard to alert the driver of a potential issue with the coolant temperature control module.

10. How important is it to address the U18A1 fault code promptly?

- It is important to address the U18A1 fault code promptly to prevent potential engine overheating, reduced performance, and other issues that may arise from the communication breakdown between modules.