AutoCodes – GMC – C128B 2017 GMC Sierra

C128B 2017 GMC Sierra Code - ABS Master Cylinder Pressure Sensor Offset Error

Quick Answer

The Electronic Brake Control Module uses inputs from the Electronic Brake Control Brake Pedal Position Sensor to determine when the brake is applied and how much force is used. Common causes include Faulty Electronic Brake Control Module (EBCM), Electronic Brake Control Module harness is open or shorted, Electronic Brake Control Module 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: C128B 2017 GMC Sierra indicates ABS Master Cylinder Pressure Sensor Offset Error.
Common causes: Common causes include Faulty Electronic Brake Control Module (EBCM), Electronic Brake Control Module harness is open or shorted, Electronic Brake Control Module 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 174

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 13, 2023

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code C128B 2017 GMC Sierra Description

The Electronic Brake Control Module uses inputs from the Electronic Brake Control Brake Pedal Position Sensor to determine when the brake is applied and how much force is used. The Electronic Brake Control Module monitors when the driver's foot is on the brake and locks the offset. The offset is locked when three out of the four inputs indicate the brake pedal is applied. The four inputs are brake pedal travel 1, brake pedal travel 2, master cylinder pressure sensor, and brake pedal position sensor. These inputs are used to determine the driver's braking intent which is used to control the amount of pressure applied to the wheels.
Brake pressure sensor information is communicated from the Electronic Brake Control Module (EBCM) to the Hybrid Control Processor (HCP). This information is used to schedule regenerative braking and engine autostops.
The Diagnostic Trouble Code (DTC) will be set when the Engine Control Module (ECM) detects a corrupted data message from the Electronic Brake Control Module.

OBDII Code C128B 2017 GMC Sierra - ABS Master Cylinder Pressure Sensor Offset Error - AutoCodes.com — C128B 2017 GMC Sierra Code - ABS Master Cylinder Pressure Sensor Offset Error

What does this mean?

What are the Possible Causes of the DTC C128B 2017 GMC Sierra?

Faulty Electronic Brake Control Module (EBCM)
Electronic Brake Control Module harness is open or shorted
Electronic Brake Control Module circuit poor electrical connection
Faulty Starter/Generator Control Module

How to Fix the DTC C128B 2017 GMC Sierra?

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 C128B 2017 GMC Sierra 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 C128B 2017 GMC Sierra code?

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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 C128B 2017 GMC Sierra Code

1. What does the OBDII code C128B mean on a 2017 GMC Sierra?

C128B indicates an ABS Master Cylinder Pressure Sensor Offset Error, meaning the brake pressure sensor is not reading properly or is out of calibration.

2. What are common symptoms of code C128B on a 2017 GMC Sierra?

Symptoms include illuminated ABS and traction control warning lights, reduced braking performance, or erratic brake pedal feel.

3. What causes code C128B on a 2017 GMC Sierra?

Common causes include a faulty master cylinder pressure sensor, wiring issues, sensor calibration problems, or a malfunctioning ABS module.

4. Can code C128B affect vehicle safety?

Yes, this code can compromise braking performance and safety systems like ABS and traction control, especially during emergency situations.

5. How do you diagnose code C128B on a 2017 GMC Sierra?

Diagnosis involves scanning for codes, inspecting the master cylinder pressure sensor and wiring, and verifying sensor readings using a diagnostic tool.

6. How can code C128B be fixed on a 2017 GMC Sierra?

Repairs may include replacing the master cylinder pressure sensor, repairing wiring issues, or recalibrating the sensor using a scan tool.

7. Can I drive my 2017 GMC Sierra with code C128B?

Driving is possible but not recommended, as the ABS system and traction control may not function correctly, compromising safety.

8. How much does it cost to repair code C128B on a 2017 GMC Sierra?

Repair costs can range from $100 to $400, depending on whether the sensor needs replacement or if wiring repairs are required.

9. Can I reset code C128B without fixing the issue?

Resetting the code without addressing the underlying issue may temporarily clear the light, but the problem will likely return.

10. Is code C128B a common issue for the 2017 GMC Sierra?

While not extremely common, this code can occur, especially if the master cylinder pressure sensor or ABS system experiences wear or electrical issues.