P279C 2018 GMC Sierra 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 2018 GMC Sierra 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 2018 GMC Sierra 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 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 P279C 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 P279C 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 P279C 2018 GMC Sierra code?
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Frequently Asked Questions about P279C 2018 GMC Sierra Code
1. What does the OBDII code P279C indicate on a 2018 GMC Sierra?
The P279C code on a 2018 GMC Sierra indicates an issue with the "Four Wheel Drive Neutral Range Performance," suggesting a malfunction in the transfer case's ability to switch into or out of neutral.
2. What are the common symptoms of code P279C in a 2018 GMC Sierra?
Common symptoms include the inability to switch the four-wheel drive system into or out of neutral, unusual noises from under the vehicle, the 4WD light blinking or remaining on, and possibly the vehicle failing to engage or disengage four-wheel drive mode.
3. What causes the P279C code to appear on my 2018 GMC Sierra?
Potential causes for the P279C code include a faulty four-wheel drive switch, damaged wiring or connectors in the four-wheel drive system, a defective transfer case actuator, or issues with the transfer case control module.
4. How can I diagnose the P279C code on my 2018 GMC Sierra?
Diagnosis involves using a scan tool to read the fault code and inspecting the four-wheel drive system components such as the switch, wiring, and actuator. Checking for additional diagnostic trouble codes can also help pinpoint the specific malfunction.
5. What are the repair steps for fixing code P279C on a 2018 GMC Sierra?
Repair steps typically include checking and replacing the four-wheel drive switch if faulty, repairing or replacing damaged wiring or connectors, replacing a faulty transfer case actuator, or reprogramming or replacing the transfer case control module if necessary.
6. Is it safe to drive my 2018 GMC Sierra with the P279C code active?
While you might still be able to drive your vehicle, it's advised to address the issue promptly as it affects the performance of the four-wheel drive system, which can be crucial in certain driving conditions and might lead to further damage if ignored.
7. Can a P279C code affect the fuel economy of my 2018 GMC Sierra?
Yes, if the four-wheel drive system is stuck in one mode due to this issue, it could potentially affect the fuel economy by causing the vehicle to operate less efficiently than designed.
8. What tools are necessary to diagnose the P279C code on a 2018 GMC Sierra?
Essential tools include a professional-grade scan tool capable of reading and clearing codes, as well as accessing real-time data from the four-wheel drive system, and basic hand tools for inspecting and repairing physical components like switches and actuators.
9. How long does it typically take to fix the P279C code on a 2018 GMC Sierra?
The repair time can vary based on the specific cause of the code, ranging from an hour for simple switch replacements to several hours for more complex issues such as wiring repairs or actuator replacements.
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