AutoCodes – Generic – C128B

C128B 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 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 1,977

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 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 - ABS Master Cylinder Pressure Sensor Offset Error - AutoCodes.com — C128B Code - ABS Master Cylinder Pressure Sensor Offset Error

What does this mean?

What are the Possible Causes of the DTC C128B?

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?

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 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

C128B Buick — ABS Master Cylinder Pressure Sensor Offset Error
C128B Cadillac — ABS Master Cylinder Pressure Sensor Offset Error
C128B Chevrolet — ABS Master Cylinder Pressure Sensor Offset Error
C128B GMC — ABS Master Cylinder Pressure Sensor Offset Error

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 Code

1. What are the common symptoms of OBDII code C128B (ABS Master Cylinder Pressure Sensor Offset Error)?

- Common symptoms include the ABS warning light illuminating on the dashboard, issues with the ABS system functionality, and potential loss of brake assistance.

2. What are the possible causes of OBDII code C128B?

- The code C128B can be triggered by a malfunction in the ABS master cylinder pressure sensor, a wiring issue, or a faulty ABS control module.

3. How can I diagnose the ABS Master Cylinder Pressure Sensor Offset Error?

- Diagnosing this error typically involves using a professional OBDII scanner to retrieve the specific fault code, inspecting the ABS sensor and related wiring for damage, and testing the sensor's functionality.

4. Can I continue driving with OBDII code C128B present?

- It is not recommended to drive with the ABS Master Cylinder Pressure Sensor Offset Error active, as it can affect the proper functioning of the ABS system and compromise brake performance.

5. How can I repair OBDII code C128B?

- Repairing this code may involve replacing the faulty ABS master cylinder pressure sensor, repairing any damaged wiring, or reprogramming the ABS control module to recalibrate the sensor.

6. Will OBDII code C128B cause my vehicle to fail an emissions test?

- While the ABS Master Cylinder Pressure Sensor Offset Error is not directly related to emissions, it is still a critical safety issue that should be addressed promptly.

7. Is it possible to reset OBDII code C128B without fixing the underlying issue?

- Resetting the code without addressing the root cause, such as a faulty sensor or wiring problem, will likely result in the error code reappearing once the ABS system is retested.

8. How much does it typically cost to repair OBDII code C128B?

- The cost of repairing OBDII code C128B can vary depending on the specific cause of the issue, but it may involve costs for parts and labor ranging from $200 to $500 or more.

9. Are there any preventive measures to avoid OBDII code C128B in the future?

- Regular maintenance and inspections of the ABS system components, including the master cylinder pressure sensor, can help prevent issues that may trigger code C128B.

10. Can I clear OBDII code C128B using a basic code reader?

- Clearing OBDII code C128B may be possible with a basic code reader, but it is important to address the underlying problem to prevent the code from reoccurring.