AutoCodes – Buick – U1821 Buick

U1821 Buick Code - Lost Communication With 14V Power 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 14V Power Module, 14V Power Module harness is open or shorted, 14V Power 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: U1821 Buick indicates Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus.
Common causes: Common causes include Faulty 14V Power Module, 14V Power Module harness is open or shorted, 14V Power 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 568

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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Table of contents Created and updated by William Orellana on Jun 07, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U1821 Buick 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 set when a supervised periodic message that includes the transmitter device availability has not been received.

OBDII Code U1821 Buick - Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus - AutoCodes.com — U1821 Buick Code - Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus

What does this mean?

What are the Possible Causes of the DTC U1821 Buick?

Faulty 14V Power Module
14V Power Module harness is open or shorted
14V Power Module circuit poor electrical connection

How to Fix the DTC U1821 Buick?

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 U1821 Buick 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.

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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 U1821 Buick Code

What does OBDII code U1821 mean on a Buick?

Code U1821 indicates a loss of communication with the 14V Power Module on the Powertrain Expansion Communication Bus, which is responsible for managing power distribution in the vehicle.

What are the symptoms of code U1821 in a Buick?

Common symptoms include illuminated warning lights (such as the check engine light), difficulty starting the vehicle, erratic electrical behavior, and possible reduced engine performance.

What causes the U1821 code to appear?

Possible causes include a faulty 14V Power Module, damaged wiring or connectors in the communication bus, power supply issues, or a malfunctioning control module.

Can I drive my Buick with code U1821?

While the vehicle may still operate, driving with this code is not recommended as it could lead to further electrical issues or even loss of critical power functions.

How do you diagnose code U1821 on a Buick?

Diagnosis involves using a scan tool to confirm the code, inspecting the wiring and connectors in the communication bus, checking the power and ground connections to the 14V Power Module, and testing the module itself.

What tools are needed to fix code U1821 in a Buick?

Tools typically include an OBDII scanner, a multimeter for checking electrical continuity and voltage, and possibly a wiring diagram for troubleshooting.

What repairs can fix code U1821?

Repairs may involve replacing the 14V Power Module, repairing or replacing damaged wiring or connectors, or reprogramming or replacing a faulty control module.

How much does it cost to fix code U1821 on a Buick?

Repair costs can vary widely, ranging from $100 for simple wiring repairs to $1,000 or more if the 14V Power Module or a control module needs replacement.

Can a low battery cause code U1821?

Yes, a low or failing battery can result in communication issues on the powertrain bus, potentially triggering the U1821 code.

Does code U1821 require reprogramming after repairs?

In some cases, reprogramming of the 14V Power Module or related control modules may be necessary after repairs to clear the code and restore proper communication.