AutoCodes – Cadillac – U1821 Cadillac

U1821 Cadillac 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 Cadillac 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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 523

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 07, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

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

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 Cadillac?

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 Cadillac 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 U1821 Cadillac code?

Need more information on how to fix the U1821 Cadillac code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the U1821 Cadillac code diagnosed by a professional: Find a repair shop in your area

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 Cadillac Code

1. What are the common symptoms of OBDII code U1821 in a Cadillac related to lost communication with the 14V power module?

- Common symptoms include issues with vehicle starting, rough idling, poor performance, and dashboard warning lights.

2. What are some potential causes of the U1821 code in a Cadillac?

- Possible causes include a faulty 14V power module, damaged wiring or connectors, software issues, or a malfunctioning powertrain control module (PCM).

3. How can I diagnose the U1821 code in my Cadillac?

- Diagnosis involves checking the wiring and connectors for damage, testing the 14V power module, and verifying communication between the modules using a diagnostic scanner.

4. Can I drive my Cadillac with the U1821 code present?

- It is not recommended to drive the vehicle with the U1821 code as it can lead to further damage and potential safety hazards. It's best to address the issue promptly.

5. How can I repair the U1821 code in my Cadillac?

- Repair may involve replacing the faulty 14V power module, repairing damaged wiring or connectors, updating software, or reprogramming the PCM.

6. Is it possible to reset the U1821 code in a Cadillac without fixing the underlying issue?

- While clearing the code may temporarily turn off the warning light, the issue causing the code will persist and likely trigger the code again until properly addressed.

7. Can a DIY enthusiast fix the U1821 code in a Cadillac?

- Depending on the individual's skill level and access to tools, some DIY enthusiasts may be able to diagnose and repair the U1821 code, but professional help is recommended for complex issues.

8. How much does it cost to repair the U1821 code in a Cadillac?

- Repair costs can vary widely depending on the specific cause of the issue, parts needed, and labor rates. It's best to consult a mechanic for an accurate estimate.

9. Are there preventive measures to avoid the U1821 code in a Cadillac?

- Regular maintenance, including checking and maintaining the electrical system, can help prevent issues leading to the U1821 code. Promptly addressing any warning lights is also crucial.

10. How long does it typically take to repair the U1821 code in a Cadillac?

- The repair time can vary based on the complexity of the issue, availability of parts, and the mechanic's workload. Some repairs can be completed within a few hours, while others may take longer.