AutoCodes – Generic – U1091

U1091 Code - Invalid Or Missing Data For Non-Legislated Diagnostics

Quick Answer

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Common causes include Faulty Module that is not communicating, Module harness is open or shorted, 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: U1091 indicates Invalid Or Missing Data For Non-Legislated Diagnostics.
Common causes: Common causes include Faulty Module that is not communicating, Module harness is open or shorted, 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 5,008

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 Apr 22, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U1091 Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, the Diagnostic Trouble Code (DTC) is set.

OBDII Code U1091 - Invalid Or Missing Data For Non-Legislated Diagnostics - AutoCodes.com — U1091 Code - Invalid Or Missing Data For Non-Legislated Diagnostics

What does this mean?

What are the Possible Causes of the DTC U1091?

Faulty Module that is not communicating
Module harness is open or shorted
Module circuit poor electrical connection

How to Fix the DTC U1091?

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 U1091 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 U1091 Code

What does OBDII code U1091 mean?

Code U1091 indicates that the vehicle's control modules are not receiving or sending valid data related to non-legislated diagnostics, often due to communication issues on the network.

What are common symptoms of code U1091?

Common symptoms include the check engine light being illuminated, issues with system monitoring, reduced engine performance, or no noticeable symptoms at all.

What causes code U1091 to appear?

Possible causes include faulty or failing control modules, wiring issues such as damaged or corroded connections, or problems with the Controller Area Network (CAN) bus communication system.

Can a loose or corroded connection trigger U1091?

Yes, a loose, damaged, or corroded wiring connection in the communication network can cause this code to appear.

How do you diagnose code U1091?

Diagnosis typically involves scanning for additional codes, inspecting the wiring and connectors in the CAN bus system, and testing the functionality of the involved control modules.

Is U1091 a serious issue?

While it may not immediately affect drivability, it can indicate underlying communication problems that could lead to more significant issues if left unaddressed.

Can clearing the code fix U1091?

Clearing the code may temporarily remove it, but the underlying issue must be diagnosed and repaired to prevent it from recurring.

What tools are needed to resolve U1091?

An OBDII scanner, a multimeter for testing electrical connections, and access to the vehicle’s wiring diagrams are typically necessary for diagnosing and repairing U1091.

Can a failing control module cause U1091?

Yes, a malfunctioning control module can fail to send or receive data correctly, leading to this code.

What steps should be taken to fix code U1091?

Inspect and repair any damaged wiring or connectors, ensure the control modules are functioning properly, and update or reprogram software if necessary.