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AutoCodes – Generic – U1023

U1023 Code - Lost Communications With Hybrid Control Module

Quick Answer

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Common causes include Faulty Hybrid Control Module (HCM), Hybrid Control Module harness is open or shorted, Hybrid 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
U1023 indicates Lost Communications With Hybrid Control Module.
Common causes
Common causes include Faulty Hybrid Control Module (HCM), Hybrid Control Module harness is open or shorted, Hybrid 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 6,674
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Apr 22, 2020
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Code U1023 Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for the state of health monitoring/node alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module node alive message. Each module on the class 2 serial data circuit is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5 seconds, a Diagnostic Trouble Code (DTC) U1023 is set.
OBDII Code U1023 - Lost Communications With Hybrid Control Module - AutoCodes.com
U1023 Code - Lost Communications With Hybrid Control Module
What does this mean?

What are the Possible Causes of the DTC U1023?

  • Faulty Hybrid Control Module (HCM)
  • Hybrid Control Module harness is open or shorted
  • Hybrid Control Module circuit poor electrical connection

How to Fix the DTC U1023?

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 U1023 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 U1023 code?

Need more information on how to fix the U1023 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U1023 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

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 U1023 Code

1. What does OBDII code U1023 mean?

Code U1023 indicates a loss of communication with the hybrid control module, which is responsible for managing the hybrid system's functions.

2. What are the common symptoms of code U1023?

Symptoms may include the hybrid system not operating properly, reduced fuel efficiency, the vehicle running on gas only, or the check engine light illuminating.

3. What causes code U1023 to appear?

Common causes include faulty wiring or connectors, a malfunctioning hybrid control module, software issues, or a failing battery control module.

4. Can I drive my car with a U1023 code?

Driving with this code may be possible but is not recommended, as it can lead to performance issues and may prevent the hybrid system from functioning correctly.

5. How is code U1023 diagnosed?

A technician will use a scan tool to verify the code, inspect wiring and connectors for damage, and test the hybrid control module and related circuits.

6. What repairs are needed to fix code U1023?

Repairs may include replacing or repairing damaged wiring, updating software, or replacing a faulty hybrid control module or related components.

7. Can a weak hybrid battery trigger code U1023?

Yes, a weak or failing hybrid battery can disrupt communication with the hybrid control module and trigger this code.

8. How much does it cost to fix a U1023 code?

Repair costs vary depending on the issue. Wiring repairs may cost a few hundred dollars, while replacing a hybrid control module could cost significantly more.

9. Can a blown fuse cause code U1023?

Yes, a blown fuse in the hybrid system's communication circuit can interrupt signals and trigger this code.

10. Is code U1023 specific to hybrid vehicles?

Yes, this code is specific to hybrid vehicles, as it relates to the hybrid control module and its communication within the vehicle's network.

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