AutoCodes – Generic – B3420

B3420 Code - Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal

Quick Answer

The front and rear suspension position sensors provide the headlamp control module with front and rear suspension position information. Common causes include Faulty Headlamp Leveling Control Module Rear Axle Sensor, Headlamp Leveling Control Module Rear Axle Sensor harness is open or shorted, Headlamp Leveling Control Module Rear Axle Sensor 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: B3420 indicates Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal.
Common causes: Common causes include Faulty Headlamp Leveling Control Module Rear Axle Sensor, Headlamp Leveling Control Module Rear Axle Sensor harness is open or shorted, Headlamp Leveling Control Module Rear Axle Sensor 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 5,479

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 Mar 08, 2020

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code B3420 Description

The front and rear suspension position sensors provide the headlamp control module with front and rear suspension position information. Each sensor receives a 5 V reference, signal, and low reference circuits from the headlamp control module. The sensors are connected to the control arms at the front and rear suspension. As the vehicle travels, the suspension compresses and rebounds moving the suspension position sensor arms. This causes the signal output of the sensors to change. The headlamp control module compares the information from the front and rear suspension position sensors and adjusts the headlamp leveling as needed. The Diagnostic Trouble Code (DTC) will set when the headlamp control module detects no signal and low voltage on the sensor signal line.

OBDII Code B3420 - Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal - AutoCodes.com — B3420 Code - Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal

What does this mean?

What are the Possible Causes of the DTC B3420?

Faulty Headlamp Leveling Control Module Rear Axle Sensor
Headlamp Leveling Control Module Rear Axle Sensor harness is open or shorted
Headlamp Leveling Control Module Rear Axle Sensor circuit poor electrical connection
Faulty Headlamp Leveling Control Module

How to Fix the DTC B3420?

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 does this mean?

Code Tech Notes

B3420 02: Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal Circuit Short to Ground
B3420 05: Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal Circuit High Voltage/Open
B3420 08: Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal Circuit Performance - Signal Invalid

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B3420 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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Information for Specific Makes

B3420 Buick — Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal
B3420 Cadillac — Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal
B3420 Chevrolet — Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal
B3420 GMC — Automatic Headlamp Leveling Control Module Rear Axle Sensor Signal

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 B3420 Code

1. What are the common symptoms of OBDII code B3420?

The common symptoms of OBDII code B3420 include malfunctioning automatic headlamp leveling control system, inaccurate headlight aiming, and dashboard warning light illumination.

2. What can cause the OBDII code B3420 to appear?

The OBDII code B3420 is typically triggered by a fault in the rear axle sensor signal of the automatic headlamp leveling control module. This can be due to sensor damage, wiring issues, or module malfunctions.

3. How can I diagnose the cause of OBDII code B3420?

Diagnosing OBDII code B3420 involves using a diagnostic scan tool to read the code from the vehicle's computer system. Further testing of the automatic headlamp leveling system, rear axle sensor, and related wiring may be needed to pinpoint the exact cause.

4. Is it safe to drive with OBDII code B3420 active?

While it may be safe to drive with OBDII code B3420 activated, it is important to address the underlying issue promptly to ensure proper functioning of the automatic headlamp leveling system, which is crucial for visibility and safety during night driving.

5. How can I repair OBDII code B3420?

Repairing OBDII code B3420 involves troubleshooting the automatic headlamp leveling control module, rear axle sensor, and wiring to identify and fix the root cause of the issue. This may include replacing a faulty sensor, repairing damaged wiring, or reprogramming the control module.

6. Can OBDII code B3420 be intermittent?

Yes, OBDII code B3420 can sometimes be intermittent, especially if the issue is related to loose connections, intermittent sensor faults, or sporadic wiring problems. It is important to address intermittent issues promptly to prevent further complications.

7. Can a DIY enthusiast fix OBDII code B3420 at home?

While some DIY enthusiasts may have the skills to diagnose and repair OBDII code B3420 at home, it is recommended to consult a professional mechanic for a proper diagnosis and repair to ensure the issue is resolved correctly and safely.

8. Will resetting the OBDII code B3420 make it go away permanently?

Resetting the OBDII code B3420 may temporarily turn off the warning light, but if the underlying issue is not addressed, the code is likely to reappear. It is important to diagnose and repair the root cause of the code for a permanent solution.

9. How much does it cost to repair OBDII code B3420?

The cost of repairing OBDII code B3420 can vary depending on the cause of the issue, the extent of the repair needed, and labor rates in your area. It is advisable to obtain a few quotes from reputable mechanics to compare costs.

10. Can OBDII code B3420 affect vehicle emissions or performance?

While OBDII code B3420 is primarily related to the automatic headlamp leveling system, unresolved issues with this code could potentially affect other vehicle systems or performance if left unaddressed. It is best to resolve the code promptly to prevent any secondary issues.