AutoCodes – GMC – P189A 2015 GMC Sierra

P189A 2015 GMC Sierra Code - Four Wheel Drive Range Secondary Signal Message Counter Incorrect

Quick Answer

The Magna Powertrain (MP) transfer case is a 1-speed automatic, Active Transfer Case (ATC). Common causes include Faulty Transfer Case Control Module, Transfer Case Control Module harness is open or shorted, Transfer Case 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: P189A 2015 GMC Sierra indicates Four Wheel Drive Range Secondary Signal Message Counter Incorrect.
Common causes: Common causes include Faulty Transfer Case Control Module, Transfer Case Control Module harness is open or shorted, Transfer Case 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.

Save to My Repairs My Repairs

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

Code Popularity 48

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 Jun 18, 2025

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 P189A 2015 GMC Sierra Description

The Magna Powertrain (MP) transfer case is a 1-speed automatic, Active Transfer Case (ATC). The MP ATC provides 3 modes, Auto 4WD, 4HI, and 2HI. The Auto 4WD position allows the capability of an active transfer case, which provides the benefits of on-demand torque biasing wet clutch and easy vehicle tuning through software calibrations. The software calibrations allow more features, such as flexible adapt ready position and clutch preload torque levels. The technology allows for vehicle speed dependent clutch toque levels to enhance the performance of the system. For example, the system is calibrated to provide 0–6.78 N•m (0–5 lb ft) of clutch torque during low speed, low engine torque operation, and predetermined higher torque for 40 km/h (25 mph) and greater. This prevents crow-hop and binding at low speeds and provides higher torque biases at higher vehicle speeds, in order to enhance stability. The Powertrain Control Module (PCM) monitors the Four Wheel Drive Range Secondary signal messages. The PCM sets the Diagnostic Trouble Code (DTC) when the Four Wheel Drive Range Secondary signal message counter is incorrect.

OBDII Code P189A 2015 GMC Sierra - Four Wheel Drive Range Secondary Signal Message Counter Incorrect - AutoCodes.com — P189A 2015 GMC Sierra Code - Four Wheel Drive Range Secondary Signal Message Counter Incorrect

What does this mean?

What are the Possible Causes of the DTC P189A 2015 GMC Sierra?

Faulty Transfer Case Control Module
Transfer Case Control Module harness is open or shorted
Transfer Case Control Module circuit poor electrical connection

How to Fix the DTC P189A 2015 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 P189A 2015 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 P189A 2015 GMC Sierra code?

Need more information on how to fix the P189A 2015 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P189A 2015 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 P189A 2015 GMC Sierra Code

What does the OBDII code P189A mean on a 2015 GMC Sierra?

P189A indicates that the Four Wheel Drive Range Secondary Signal Message Counter is incorrect, meaning there is a communication issue between the transfer case control module and other vehicle systems.

What are common symptoms of the P189A code on a 2015 GMC Sierra?

Symptoms may include the four-wheel-drive system not functioning properly, warning lights on the dashboard, or difficulty shifting into certain drive modes.

What causes the P189A code on a 2015 GMC Sierra?

Common causes include a faulty transfer case control module, wiring issues, or problems with the communication signals between modules.

Can a weak battery cause the P189A code on a 2015 GMC Sierra?

Yes, a weak or failing battery can affect communication signals and contribute to this code being triggered.

How do I diagnose the P189A code on a 2015 GMC Sierra?

Diagnosis typically involves scanning for other related codes, inspecting the transfer case control module, and checking the wiring and connections for damage or corrosion.

Is it safe to drive with the P189A code on a 2015 GMC Sierra?

Driving with this code may not be safe if it impacts your ability to switch into four-wheel drive or if the vehicle enters a failsafe mode. Prompt diagnosis and repair are recommended.

How can the P189A code be fixed on a 2015 GMC Sierra?

Repairs may include replacing the transfer case control module, fixing damaged wiring, or reprogramming the module to restore proper communication.

Does the P189A code require professional repair?

While some issues like checking connections can be done by a DIYer, diagnosing and repairing module-related problems often require professional tools and expertise.

Can updating software resolve the P189A code on a 2015 GMC Sierra?

Yes, in some cases, updating the vehicle’s control module software can resolve communication issues and clear this code.

What tools are needed to fix the P189A code on a 2015 GMC Sierra?

A professional-grade OBDII scanner, multimeter for testing electrical connections, and possibly reprogramming tools may be needed for proper diagnosis and repair.