P279C GMC Code - Four Wheel Drive Neutral 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
- P279C GMC indicates Four Wheel Drive Neutral 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 P279C 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 P279C 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 P279C 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 P279C 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.
Need more information about the P279C GMC code?
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Need Help with the Code?
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Information for Specific GMC Models
- P279C 2014 GMC Sierra — Four Wheel Drive Neutral Range Performance
- P279C 2015 GMC Sierra — Four Wheel Drive Neutral Range Performance
- P279C 2016 GMC Sierra — Four Wheel Drive Neutral Range Performance
- P279C 2017 GMC Sierra — Four Wheel Drive Neutral Range Performance
- P279C 2018 GMC Sierra — Four Wheel Drive Neutral Range Performance
Frequently Asked Questions about P279C GMC Code
1. What does the OBDII code P279C mean on a GMC vehicle?
P279C indicates a "Four Wheel Drive Neutral Range Performance" issue, meaning the vehicle's transfer case system is not engaging or operating in the neutral range as expected.
2. What are common symptoms of the P279C code?
Symptoms may include the 4WD system not shifting into neutral, the service 4WD light illuminating, unusual noises from the transfer case, or the vehicle being stuck in a specific drive mode.
3. What causes the P279C code to be triggered?
Common 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 I continue driving with the P279C code?
While the vehicle may still be drivable in some cases, ignoring this code can lead to further damage to the 4WD system. It’s best to address the issue promptly.
5. How is the P279C code diagnosed?
A technician will use a scan tool to verify the code, inspect the transfer case wiring and connectors, test the transfer case shift motor, and check for mechanical issues in the transfer case assembly.
6. How do I fix the P279C code on my GMC?
Repairs may involve replacing the transfer case shift motor, repairing damaged wiring or connectors, reprogramming or replacing the transfer case control module, or addressing internal transfer case damage.
7. Can a bad transfer case motor cause the P279C code?
Yes, a faulty transfer case shift motor is a common cause of this code as it prevents the system from shifting into the neutral range.
8. How much does it cost to fix the P279C code?
Repair costs can vary widely but may range from $300 to $1,500 depending on whether the issue is electrical (e.g., wiring or motor replacement) or mechanical (e.g., transfer case repair).
9. Can a software update fix the P279C code?
In some cases, a software update for the transfer case control module may resolve the code if it’s caused by a programming issue.
10. What tools are needed to diagnose the P279C code?
A professional-grade scan tool, a multimeter for testing electrical components, and potentially specialized tools for inspecting or disassembling the transfer case are needed for diagnosis.
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