Engine-Codes - Generic - U1821

U1821 - Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3  What is this?
Table of contents

U1821 Possible Causes

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

How is the U1821 code repair?

Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

What is the cost to diagnose the U1821 code

Labor: 1.0

The cost to diagnose the U1821 code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.
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Possible Symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

U1821 Meaning

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.

More Information

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Information for specific makes

  • U1821 BUICK Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus
  • U1821 CADILLAC Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus
  • U1821 CHEVROLET Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus
  • U1821 GMC Lost Communication With 14V Power Module On Powertrain Expansion Communication Bus

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