AutoCodes – Generic – B2791

B2791 Code - Communication Condition Failure Between ECM

Quick Answer

This Diagnostic Trouble Code (DTC) is output when the ID Code Box does not respond to a verification request signal from the Engine Control Module (ECM). Common causes include Faulty ID Code Box, ID Code Box harness is open or shorted, ID Code Box 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: B2791 indicates Communication Condition Failure Between ECM.
Common causes: Common causes include Faulty ID Code Box, ID Code Box harness is open or shorted, ID Code Box 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 1,288

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 Feb 06, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code B2791 Description

This Diagnostic Trouble Code (DTC) is output when the ID Code Box does not respond to a verification request signal from the Engine Control Module (ECM).

OBDII Code B2791 - Communication Condition Failure Between ECM - AutoCodes.com — B2791 Code - Communication Condition Failure Between ECM

What does this mean?

What are the Possible Causes of the DTC B2791?

Faulty ID Code Box
ID Code Box harness is open or shorted
ID Code Box circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC B2791?

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 B2791 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 B2791 code?

Need more information on how to fix the B2791 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the B2791 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

B2791 Lexus — Communication Condition Failure Between ECM
B2791 Nissan — Electric Compressor Low Speed High Load
B2791 Scion — Communication Condition Failure Between ECM
B2791 Toyota — Communication Condition Failure Between ECM

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 B2791 Code

1. What are the common symptoms of OBDII code B2791 related to Communication Condition Failure Between ECM?

- Common symptoms include the check engine light being illuminated, issues with engine performance, and possible problems with vehicle transmission.

2. What are the potential causes of OBDII code B2791?

- The code B2791 can be triggered by issues such as faulty ECM connections, damaged wiring harnesses, or a malfunctioning ECM itself.

3. How can I diagnose the Communication Condition Failure Between ECM issue?

- Diagnosing this issue typically involves using a scan tool to retrieve the specific fault code, checking the ECM connections for any loose or damaged wires, and testing the ECM for proper functionality.

4. Can I drive my vehicle with OBDII code B2791 present?

- It is not recommended to drive your vehicle with the B2791 code active, as it can lead to potential performance issues and further damage if left unresolved.

5. How can I repair OBDII code B2791?

- Repairing code B2791 involves addressing the root cause, which may include fixing faulty connections, repairing damaged wiring, or replacing the ECM if necessary.

6. Will resetting the ECM clear the B2791 code?

- Resetting the ECM may temporarily clear the code, but it is important to diagnose and address the underlying issue causing the Communication Condition Failure to prevent the code from reoccurring.

7. Can a DIY enthusiast fix OBDII code B2791?

- Depending on the cause of the issue, DIY enthusiasts with automotive repair experience may be able to address the B2791 code by checking and repairing connections or wiring. However, more complex issues may require professional help.

8. Is it necessary to visit a mechanic for OBDII code B2791?

- If you are unsure about diagnosing or repairing the B2791 code yourself, it is recommended to visit a qualified mechanic who can properly identify and fix the issue to prevent further complications.

9. How much does it cost to repair OBDII code B2791?

- The cost of repairing the B2791 code can vary depending on the underlying cause and the extent of the repairs needed. Costs may include parts and labor for repairing connections, wiring, or replacing the ECM.

10. Are there any preventive measures to avoid OBDII code B2791 in the future?

- To prevent the Communication Condition Failure Between ECM issue, regular maintenance checks, ensuring proper connections, and addressing any warning signs promptly can help avoid triggering the B2791 code.