AutoCodes – GMC – B3420 GMC

B3420 GMC 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 GMC 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 865

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

What does this mean?

What are the Possible Causes of the DTC B3420 GMC?

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 GMC?

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 GMC 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 B3420 GMC Code

What are common symptoms of OBDII code B3420 GMC?

- Common symptoms of OBDII code B3420 GMC include malfunctioning automatic headlamp leveling control, erratic headlight behavior, and dashboard warning lights related to the headlamp system.

What are possible causes of OBDII code B3420 GMC?

- Possible causes of OBDII code B3420 GMC include a faulty rear axle sensor, damaged wiring or connectors, a malfunctioning automatic headlamp leveling control module, or a problem with the headlamp system calibration.

How can I diagnose the cause of OBDII code B3420 GMC?

- To diagnose the cause of OBDII code B3420 GMC, you can use a diagnostic scanner to retrieve the trouble code and perform a visual inspection of the rear axle sensor, wiring, and connectors. Testing the automatic headlamp leveling control module and recalibrating the headlamp system may also be necessary.

What are the repair options for OBDII code B3420 GMC?

- Repair options for OBDII code B3420 GMC include replacing the rear axle sensor if it is faulty, repairing any damaged wiring or connectors, replacing the automatic headlamp leveling control module if needed, and recalibrating the headlamp system to ensure proper functionality.

Can I drive my vehicle with OBDII code B3420 GMC?

- It is not recommended to drive your vehicle with OBDII code B3420 GMC, as the malfunctioning automatic headlamp leveling control system can affect headlight alignment and visibility, compromising safety on the road. It is best to address the issue promptly.

How much does it cost to repair OBDII code B3420 GMC?

- The cost to repair OBDII code B3420 GMC can vary depending on the specific cause of the issue, the parts needed for replacement, and labor costs. It is advisable to consult with a professional mechanic or dealership for an accurate estimate.

Is OBDII code B3420 GMC a common issue in GMC vehicles?

- OBDII code B3420 GMC related to the automatic headlamp leveling control module rear axle sensor signal may occur in certain GMC vehicles equipped with this system. It is not uncommon, and proper maintenance can help prevent this issue.

What should I do if OBDII code B3420 GMC keeps coming back after repair?

- If OBDII code B3420 GMC keeps coming back after repair, it is important to recheck the rear axle sensor, wiring, and connectors for any overlooked issues. The automatic headlamp leveling control module and headlamp system calibration should also be inspected for proper functioning. Consulting a professional may be necessary.