AutoCodes – Generic – U1818

U1818 Code - Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus

Quick Answer

Devices connected to the powertrain high-speed General Motor Local Area Network (GMLAN) 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: U1818 indicates Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus.
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 5,231

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 Aug 09, 2023

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U1818 Description

Devices connected to the powertrain high-speed General Motor Local Area Network (GMLAN) 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 be set when a supervised periodic message that includes the transmitter device availability has not been received.

OBDII Code U1818 - Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus - AutoCodes.com — U1818 Code - Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus

What does this mean?

What are the Possible Causes of the DTC U1818?

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 U1818?

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 U1818 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 U1818 code?

Need more information on how to fix the U1818 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U1818 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

U1818 Buick — Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus
U1818 Cadillac — Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus
U1818 Chevrolet — Lost Communication with Engine Control Module on Powertrain Expansion Communication Bus
U1818 GMC — Lost Communication with Engine Control Module on Powertrain Expansion Communication 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 U1818 Code

1. What does OBDII code U1818 mean?

U1818 indicates a loss of communication between the Engine Control Module (ECM) and the powertrain expansion communication bus, which may cause malfunctions in critical vehicle systems.

2. What are the common symptoms of code U1818?

Symptoms may include a check engine light, reduced engine performance, transmission shifting issues, or failure to start.

3. What causes the U1818 code to appear?

Common causes include faulty wiring or connectors in the communication bus, a malfunctioning ECM, software issues, or network interference.

4. Can a dead battery trigger the U1818 code?

Yes, a weak or dead battery can disrupt communication on the powertrain bus, potentially triggering this code.

5. Is it safe to drive with a U1818 code?

Driving with this code is not recommended, as it may lead to unpredictable engine or transmission behavior.

6. How can I diagnose the U1818 code?

Start by inspecting the wiring and connectors for damage or corrosion, check for other related codes, and test the ECM communication circuits with a scan tool.

7. Can a faulty ECM cause the U1818 code?

Yes, a malfunctioning ECM can fail to communicate properly with the powertrain bus, resulting in this code.

8. What tools are needed to troubleshoot the U1818 code?

Youâ€™ll need an OBDII scan tool, a multimeter for testing wiring, and potentially an oscilloscope to analyze communication signals.

9. How do I fix the U1818 code?

Repairs may involve repairing or replacing damaged wiring, cleaning or replacing corroded connectors, updating ECM software, or replacing the ECM if necessary.

10. Will clearing the code fix the issue permanently?

Clearing the code may reset the system temporarily, but the underlying issue causing the communication loss must be addressed to prevent the code from returning.