P279B GMC 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 GMC 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.
Code P279B GMC Description
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.
What are the Possible Causes of the DTC P279B GMC?
- 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 GMC?
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 GMC 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 GMC Models
- P279B 2014 GMC Sierra — Four Wheel Drive Low Range Performance
- P279B 2015 GMC Sierra — Four Wheel Drive Low Range Performance
- P279B 2016 GMC Sierra — Four Wheel Drive Low Range Performance
- P279B 2017 GMC Sierra — Four Wheel Drive Low Range Performance
- P279B 2018 GMC Sierra — Four Wheel Drive Low Range Performance
Frequently Asked Questions about P279B GMC Code
1. What does the OBDII code P279B mean on a GMC vehicle?
The P279B code indicates an issue with the Four-Wheel Drive (4WD) Low Range Performance, meaning the transfer case may not be engaging or functioning properly in low range mode.
2. What are the common symptoms of the P279B code?
Common symptoms include the 4WD warning light illuminating, inability to engage low range mode, reduced off-road performance, or unusual noises from the transfer case.
3. What causes the P279B code to appear on a GMC vehicle?
Possible causes include a faulty transfer case shift motor, damaged wiring or connectors, a malfunctioning transfer case control module, or mechanical issues within the transfer case.
4. Can driving with the P279B code damage my GMC?
While you can typically drive in 2WD or high-range 4WD, ignoring the issue may worsen transfer case or drivetrain damage over time if not addressed.
5. How do I diagnose the P279B code on my GMC?
Start by checking the transfer case wiring and connectors for damage or corrosion, inspecting the shift motor, and using a diagnostic scanner to monitor the transfer case control module's performance.
6. How do I fix the P279B code on a GMC vehicle?
Repairs may include replacing the transfer case shift motor, repairing damaged wiring, reprogramming or replacing the transfer case control module, or addressing internal transfer case issues.
7. Is the transfer case shift motor often the cause of the P279B code?
Yes, a malfunctioning transfer case shift motor is a common cause, as it may fail to properly engage low range mode.
8. Can low transfer case fluid cause the P279B code?
Yes, low or contaminated transfer case fluid can lead to poor performance and trigger the P279B code.
9. How much does it cost to repair the P279B code on a GMC?
Repair costs vary but typically range from $200 to $1,500, depending on whether the issue is with the shift motor, wiring, or transfer case.
10. Can I clear the P279B code without fixing the issue?
You can clear the code with a diagnostic scanner, but it will likely return if the underlying problem isn’t resolved.
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