AutoCodes – Generic – C0638

C0638 Code - Left Front Normal Force Circuit High

Quick Answer

The Continuously Variable Road Sensing Suspension (CVRSS) module estimates the road surface and communicates that information to the Electronic Brake Control module (EBCM). Common causes include Faulty Electronic Brake Control module (EBCM), Electronic Brake Control module (EBCM) harness is open or shorted, Electronic Brake Control module (EBCM) 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: C0638 indicates Left Front Normal Force Circuit High.
Common causes: Common causes include Faulty Electronic Brake Control module (EBCM), Electronic Brake Control module (EBCM) harness is open or shorted, Electronic Brake Control module (EBCM) 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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 2,255

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 Jul 30, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code C0638 Description

The Continuously Variable Road Sensing Suspension (CVRSS) module estimates the road surface and communicates that information to the Electronic Brake Control module (EBCM). The CVRSS module provides a Pulse Width Modulation (PWM) signal to the EBCM through the left and right normal force signal circuits. The CVRSS module sends each normal force value twice to the EBCM. The possible values of the PWM duty cycle are 20%, 40%, 60% and 80%, with the valid range from 10-90%. The EBCM uses this information to provide improved rough-road braking performance.

OBDII Code C0638 - Left Front Normal Force Circuit High - AutoCodes.com — C0638 Code - Left Front Normal Force Circuit High

What does this mean?

What are the Possible Causes of the DTC C0638?

Faulty Electronic Brake Control module (EBCM)
Electronic Brake Control module (EBCM) harness is open or shorted
Electronic Brake Control module (EBCM) circuit poor electrical connection

How to Fix the DTC C0638?

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 C0638 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 C0638 code?

Need more information on how to fix the C0638 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the C0638 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

C0638 Buick — Left Front Normal Force Circuit High
C0638 Cadillac — Left Front Normal Force Circuit High
C0638 Chevrolet — Left Front Normal Force Circuit High
C0638 GMC — Left Front Normal Force Circuit High

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 C0638 Code

What does the OBDII code C0638 mean?

The OBDII code C0638 indicates a problem with the left front normal force circuit, specifically that the circuit is reading a high voltage or signal that is outside the expected range.

What are common symptoms associated with code C0638?

Common symptoms may include warning lights on the dashboard, such as the ABS or traction control light, and potentially altered handling characteristics or stability issues while driving.

What could cause the C0638 code to trigger?

Causes can include a faulty left front wheel speed sensor, damaged wiring or connectors in the normal force circuit, or issues with the ABS control module.

Can I drive my vehicle with code C0638?

While you can technically drive your vehicle, it is not recommended due to potential safety issues like decreased braking efficiency or compromised traction control.

How can I diagnose the C0638 code?

To diagnose the C0638 code, check the vehicle's wiring and connections for damage, test the left front wheel speed sensor for proper operation, and use a scan tool to assess the ABS control module for additional codes.

What repairs can be made to fix code C0638?

Repairs may include replacing a faulty left front wheel speed sensor, repairing damaged wiring or connectors, or replacing the ABS control module if it is determined to be faulty.

Is code C0638 a serious issue?

Yes, code C0638 can be serious because it affects the vehicle's braking and stability control systems, which are crucial for safe driving.

How can I reset the C0638 code after repairs?

After making the necessary repairs, you can reset the C0638 code using an OBDII scanner, or by disconnecting the vehicle's battery for a few minutes and then reconnecting it.

What should I do if the C0638 code returns after repairs?

If the C0638 code returns, it is advisable to recheck all connections and components involved in the normal force circuit and consider seeking professional diagnostic help to identify any underlying issues.