P279A 2018 GMC Sierra Code - Four Wheel Drive High 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
- P279A 2018 GMC Sierra indicates Four Wheel Drive High 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 P279A 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 P279A 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 P279A 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 P279A 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 P279A 2018 GMC Sierra code?
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Frequently Asked Questions about P279A 2018 GMC Sierra Code
1. What does the OBDII code P279A mean on a 2018 GMC Sierra?
P279A indicates an issue with the Four-Wheel Drive (4WD) High Range Performance, which means the system is not functioning as expected in 4WD high mode.
2. What are the common symptoms of code P279A on a 2018 GMC Sierra?
Symptoms may include the 4WD system not engaging properly, illumination of the Check Engine Light or Service 4WD light, and reduced off-road or traction performance.
3. What causes the P279A code on a GMC Sierra?
Potential causes include a malfunctioning transfer case motor, damaged wiring or connectors in the 4WD system, a faulty transfer case control module, or mechanical issues within the transfer case itself.
4. Can driving with the P279A code damage my GMC Sierra?
Driving with this code may not immediately harm the vehicle, but it can lead to reduced traction in challenging conditions and potential long-term damage to the 4WD system if left unresolved.
5. How is the P279A code diagnosed?
A technician typically uses a scan tool to read the code, inspects the transfer case motor and wiring, checks for mechanical wear in the transfer case, and tests the transfer case control module for faults.
6. How can I fix the P279A code on my 2018 GMC Sierra?
Repairs may include replacing the transfer case motor, repairing or replacing damaged wiring or connectors, updating or replacing the transfer case control module, or addressing mechanical damage in the transfer case.
7. Is the P279A code covered under warranty for a 2018 GMC Sierra?
Coverage depends on your warranty terms. If your vehicle is still under a powertrain or drivetrain warranty, it may cover repairs related to the 4WD system.
8. Can low transfer case fluid cause the P279A code?
Yes, low or contaminated transfer case fluid can cause mechanical issues, which may trigger the P279A code. Checking and replacing the fluid is a good first step.
9. How much does it cost to repair the P279A code on a GMC Sierra?
Repair costs can vary depending on the exact issue but may range from $200 for minor repairs like wiring fixes to $1,500 or more for replacing the transfer case motor or control module.
10. Can I fix the P279A code myself?
If you're experienced with automotive repairs, you may be able to inspect and replace components like the transfer case motor or fluid. However, diagnosing electrical or control module issues may require professional tools and expertise.
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