AutoCodes – GMC – P279B 2018 GMC Sierra

P279B 2018 GMC Sierra Code - Four Wheel Drive Low Range Performance

Quick Answer

The Engine Control Module (ECM) uses the following two ways to determine if the transfer case is in 4WD Low, 4WD High, or Neutral. Common causes include Reprogram Engine Control Module (ECM), Faulty Engine Control Module, Engine Control Module harness is open or shorted. 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: P279B 2018 GMC Sierra indicates Four Wheel Drive Low Range Performance .
Common causes: Common causes include Reprogram Engine Control Module (ECM), Faulty Engine Control Module, Engine Control Module harness is open or shorted.
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 245

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 Aug 29, 2022

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P279B 2018 GMC Sierra Description

The Engine Control Module (ECM) uses the following two ways to determine if the transfer case is in 4WD Low, 4WD High, or Neutral.
1. The first way is to compare the transmission output speed sensor to the transfer case output speed sensor in order to calculate the transfer case range.
2. The second way is to use a LAN message sent by the transfer case shift control module to the ECM.
The ECM uses this message to determine motor torque required and transmission shifting.
The internal fault detection is handled inside the control module. No external circuit diagnosis is involved.
If the first way and second way of determining transfer case range do not match while in 4WD Low, 4WD High or Neutral, then the Diagnostic Trouble Code (DTC) is set.

OBDII Code P279B 2018 GMC Sierra - Four Wheel Drive Low Range Performance - AutoCodes.com — P279B 2018 GMC Sierra Code - Four Wheel Drive Low Range Performance

What does this mean?

What are the Possible Causes of the DTC P279B 2018 GMC Sierra?

Reprogram Engine Control Module (ECM)
Faulty Engine Control Module
Engine Control Module harness is open or shorted
Engine Control Module circuit poor electrical connection
Transmission internal mechanical problems

How to Fix the DTC P279B 2018 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 P279B 2018 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 P279B 2018 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 P279B 2018 GMC Sierra Code

1. What does the OBDII code P279B mean on a 2018 GMC Sierra?

P279B indicates a "Four Wheel Drive Low Range Performance" issue, meaning the vehicle's system is detecting a problem with engaging or performing in 4WD low range mode.

2. What are the common symptoms of a P279B code on a GMC Sierra?

Symptoms include trouble shifting into 4WD low, a 4WD warning light on the dashboard, reduced off-road performance, and possibly a check engine light.

3. What causes the P279B code to appear on a 2018 GMC Sierra?

Common causes include a faulty transfer case motor, wiring issues, a damaged 4WD control module, or mechanical problems in the transfer case.

4. Can a bad transfer case motor trigger the P279B code?

Yes, a malfunctioning transfer case motor can prevent proper engagement of 4WD low range and trigger the P279B code.

5. How is the P279B code diagnosed in a 2018 GMC Sierra?

Diagnosis typically involves scanning for codes with an OBDII scanner, inspecting the transfer case motor, checking the wiring and connectors, and testing the 4WD control module.

6. Is it safe to drive with the P279B code active?

While the vehicle may still operate in 2WD or 4WD high, using 4WD low could cause further damage. It is best to address the issue promptly.

7. How can I fix the P279B code on my GMC Sierra?

Repairs may involve replacing the transfer case motor, repairing wiring issues, reprogramming or replacing the 4WD control module, or servicing the transfer case if it is mechanically damaged.

8. Can low transfer case fluid cause a P279B code?

Yes, low or contaminated transfer case fluid can lead to mechanical issues that affect 4WD low performance, potentially triggering this code.

9. Will resetting the code fix the P279B issue?

Clearing the code without addressing the underlying issue is only a temporary solution. The code will likely return if the problem persists.

10. How much does it cost to repair a P279B code on a 2018 GMC Sierra?

Repair costs vary depending on the issue. Replacing a transfer case motor may cost $300-$700, while more extensive repairs like transfer case servicing or module replacement can exceed $1,000.