AutoCodes – Scion – B2791 Scion

B2791 Scion 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 Scion 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 427

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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

What does this mean?

What are the Possible Causes of the DTC B2791 Scion?

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 Scion?

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 Scion 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 B2791 Scion Code

1. What does the OBDII code B2791 mean for a Scion?

Code B2791 indicates a communication failure between the Engine Control Module (ECM) and the immobilizer system, often related to the vehicleâ€™s anti-theft system.

2. What are common symptoms of code B2791 in a Scion?

Symptoms may include the engine not starting, the security light staying on or flashing, and stored trouble codes related to the immobilizer.

3. What causes code B2791 in a Scion?

Common causes include a faulty ECM, a malfunctioning immobilizer, damaged wiring or connectors, or a key that isnâ€™t programmed correctly.

4. Can a weak car battery trigger code B2791?

Yes, a weak or failing car battery can disrupt communication between the ECM and immobilizer, potentially triggering this code.

5. How is code B2791 diagnosed in a Scion?

A technician will use an OBDII scanner to confirm the code, inspect the wiring and connectors for damage, and test the ECM and immobilizer system for proper functionality.

6. Can I still drive my Scion with code B2791 active?

Likely not, as this code often results in the engine failing to start due to the immobilizer system preventing ignition.

7. How do you fix code B2791 in a Scion?

Repairs might include reprogramming the key, replacing faulty components like the ECM or immobilizer, and repairing or replacing damaged wiring or connectors.

8. Does code B2791 always mean the ECM is bad?

No, the issue could also lie with the immobilizer system, key programming, or wiring, so a thorough diagnosis is necessary.

9. How much does it cost to fix code B2791 in a Scion?

Repair costs can vary widely depending on the root cause, ranging from $100 for reprogramming the key to over $1,000 for ECM replacement.

10. Can a DIY approach fix code B2791 in a Scion?

Basic checks like inspecting wiring or replacing a weak battery might be done by DIYers, but reprogramming keys or diagnosing the ECM typically requires professional tools and expertise.