AutoCodes – Cadillac – U1804 Cadillac

U1804 Cadillac Code - Lost Communication With Inside Rearview Mirror Control Module

Quick Answer

Modules connected to the Controller Area Network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Common causes include Faulty Inside Rearview Mirror Control Module, Inside Rearview Mirror Control Module harness is open or shorted, Inside Rearview Mirror 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: U1804 Cadillac indicates Lost Communication With Inside Rearview Mirror Control Module.
Common causes: Common causes include Faulty Inside Rearview Mirror Control Module, Inside Rearview Mirror Control Module harness is open or shorted, Inside Rearview Mirror 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 492

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
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Code U1804 Cadillac Description

Modules connected to the Controller Area Network (CAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module. A module with a CAN serial data circuits malfunction or which loses power during the current ignition cycle will have a Loss of Communication Diagnostic Trouble Code (DTC) set by other modules that depend on information from that failed module. If any of the CAN circuit are shorted to battery voltage, ground, or between them no communication is possible on the CAN serial data bus, a Diagnostic Trouble Code will set.

OBDII Code U1804 Cadillac - Lost Communication With Inside Rearview Mirror Control Module - AutoCodes.com — U1804 Cadillac Code - Lost Communication With Inside Rearview Mirror Control Module

What does this mean?

What are the Possible Causes of the DTC U1804 Cadillac?

Faulty Inside Rearview Mirror Control Module
Inside Rearview Mirror Control Module harness is open or shorted
Inside Rearview Mirror Control Module circuit poor electrical connection

How to Fix the DTC U1804 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 U1804 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.

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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 U1804 Cadillac Code

What does the OBDII code U1804 mean in a Cadillac?

The OBDII code U1804 indicates "Lost Communication With Inside Rearview Mirror Control Module," meaning the vehicle's computer is unable to communicate with the rearview mirror module.

What symptoms might a driver experience with the U1804 code?

Common symptoms include malfunctioning features of the rearview mirror, such as auto-dimming, GPS, or integrated camera functions, and potential warning lights on the dashboard.

What could cause the U1804 code to trigger?

Possible causes include a faulty inside rearview mirror control module, damaged wiring or connectors, a blown fuse, or issues with the vehicle's main communication network.

How can I diagnose the U1804 code?

To diagnose the U1804 code, start by checking the wiring and connectors for damage, testing the rearview mirror control module for functionality, and inspecting the vehicle's fuses related to the mirror system.

Are there any common repairs for the U1804 code?

Common repairs may involve replacing the inside rearview mirror control module, repairing damaged wiring or connectors, or replacing blown fuses.

Can I drive my Cadillac with the U1804 code active?

While it is generally safe to drive, you may experience issues with the rearview mirror's features, which could affect visibility and safety. It's advisable to address the code promptly.

How can I reset the U1804 code after repairs?

You can reset the U1804 code using an OBDII scanner by clearing the trouble codes from the vehicle's computer after completing the necessary repairs.

Is U1804 code specific to Cadillac vehicles?

No, the U1804 code is not exclusive to Cadillac; it can appear in various GM vehicles and other makes that utilize similar communication protocols.

What should I do if the U1804 code returns after repairs?

If the U1804 code returns after repairs, further diagnostic testing may be needed to identify underlying issues, such as problems with the vehicle's communication bus or additional faults in related modules.