AutoCodes – Generic – B2721

B2721 Code - PASS-Key Detection Circuit

Quick Answer

The Body Control Module (BCM) supplies a 5 volt signal and a ground circuit for the PASS-KeyÂ® system. Common causes include Faulty Ignition Key, Faulty Ignition Lock Cylinder, Faulty Body Control Module (BCM). 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: B2721 indicates PASS-Key Detection Circuit.
Common causes: Common causes include Faulty Ignition Key, Faulty Ignition Lock Cylinder, Faulty Body Control Module (BCM).
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 4,461

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 Jan 26, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code B2721 Description

The Body Control Module (BCM) supplies a 5 volt signal and a ground circuit for the PASS-KeyÂ® system. This allows the BCM to detect PASS-KeyÂ® resistance values. Inserting the PASS-KeyÂ® (with resistor pellet) in the ignition lock cylinder completes the PASS-KeyÂ® circuit. Contacts in the ignition lock cylinder mate with the pellet contacts. The BCM compares the resistance value of the key pellet to the valid resistance programmed into the BCM. If the proper resistance value is read, the BCM allows the following functions to occur: The theft deterrent relay to energize, The steering column to unlock and The BCM sends a message through the serial data line to the Powertrain Control Module (PCM) to enable fuel delivery. If the resistance value is incorrect, a malfunction is present and a DTC will set.

OBDII Code B2721 - PASS-Key Detection Circuit - AutoCodes.com — B2721 Code - PASS-Key Detection Circuit

What does this mean?

What are the Possible Causes of the DTC B2721?

Faulty Ignition Key
Faulty Ignition Lock Cylinder
Faulty Body Control Module (BCM)

How to Fix the DTC B2721?

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 B2721 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 B2721 code?

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Need Help with the Code?

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Information for Specific Makes

B2721 Buick — PASS-Key Detection Circuit
B2721 Cadillac — PASS-Key Detection Circuit
B2721 Chevrolet — PASS-Key Detection Circuit
B2721 Ford — Liftgate/Decklid Ajar Output Short To Ground Or Open
B2721 GMC — PASS-Key Detection Circuit
B2721 Infiniti — Rear Sonar Sensor Left Inner
B2721 Lincoln — Liftgate/Decklid Ajar Output Short To Ground Or Open
B2721 Mercury — Liftgate/Decklid Ajar Output Short To Ground Or Open
B2721 Nissan — Rear Sonar Sensor Left Inner

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 B2721 Code

1. What are the common symptoms of OBDII code B2721 PASS-Key Detection Circuit?

- The common symptoms include issues with starting the vehicle, intermittent stalling, and the security light staying on.

2. What are the possible causes of OBDII code B2721 PASS-Key Detection Circuit?

- Possible causes include a faulty ignition key, a malfunctioning PASS-Key module, wiring issues, or a problem with the ignition lock cylinder.

3. How can I diagnose the OBDII code B2721 PASS-Key Detection Circuit?

- Diagnosis involves checking the ignition key, inspecting the PASS-Key module and related wiring, and testing the ignition lock cylinder for proper operation.

4. Can I drive my vehicle with OBDII code B2721 PASS-Key Detection Circuit?

- It is not recommended to drive the vehicle with this code as it may lead to starting issues and potential stalling, posing a safety risk.

5. How do I repair OBDII code B2721 PASS-Key Detection Circuit?

- Repair typically involves replacing a faulty ignition key, repairing or replacing the PASS-Key module, addressing wiring issues, or fixing problems with the ignition lock cylinder.

6. Why is it important to fix OBDII code B2721 PASS-Key Detection Circuit promptly?

- Prompt repair is essential to ensure the proper functioning of the vehicle's security system and to prevent potential starting and stalling issues.

7. Can OBDII code B2721 PASS-Key Detection Circuit be reset without repairs?

- Resetting the code without addressing the underlying issue may temporarily turn off the warning light, but the problem will likely reoccur.

8. Are there any DIY tips for troubleshooting OBDII code B2721 PASS-Key Detection Circuit?

- DIY tips include checking the ignition key for damage, inspecting the PASS-Key module connections, and ensuring proper wiring connections.

9. How long does it typically take to repair OBDII code B2721 PASS-Key Detection Circuit?

- The repair time can vary depending on the specific cause of the code, but it may take anywhere from 1-3 hours to diagnose and fix the issue.

10. Can a mechanic help me with OBDII code B2721 PASS-Key Detection Circuit?

- Yes, a qualified mechanic with experience in automotive electrical systems can diagnose and repair OBDII code B2721 PASS-Key Detection Circuit efficiently.