By Samuel The P1399 code on your GMC vehicle indicates an issue with the exhaust gas recirculation (EGR) system, which can lead to decreased engine performance, poor fuel economy, and higher emissions.
Symptoms of this issue include rough idling, lack of power, and poor fuel efficiency.
The problem could be a faulty EGR valve, blockage in the vacuum hose, or a worn-out temperature sensor.
To fix the issue, you'll need to diagnose the problem using a code reader and other tools, then follow a step-by-step repair guide.
What does this Code Mean
When your GMC's computer shows a P1399 code, it means there's a problem with the exhaust gas recirculation (EGR) system.
The EGR system helps reduce bad emissions by sending some of the engine's exhaust gas back into the cylinders.
If the EGR system isn't working right, it can cause more emissions, make the engine work less well, and even damage the engine.
You need to fix this problem as soon as possible to prevent more damage.
What are the Symptoms
The symptoms of a P1399 code issue with the EGR system may include:
- Decreased engine performance: The engine lacks power or hesitates when accelerating.
- Rough idling: The engine idles unevenly or stalls frequently.
- Poor fuel economy: Fuel consumption increases significantly.
- Increased emissions: The vehicle emits more pollutants than usual.
- Illuminated "check engine" light: The warning light on the dashboard comes on.
What are the Causes
The P1399 code issue with the EGR system is caused by several factors.
These factors include:
- A faulty or clogged EGR valve, which can prevent the system from working properly and trigger the P1399 code.
- A blockage or leak in the vacuum hose, which can disrupt the EGR system's operation and result in the code.
- A faulty or worn-out EGR temperature sensor, which can provide incorrect readings and cause the EGR system to malfunction.
- Using poor or low-quality fuel, which can lead to deposits and residue buildup in the EGR system and cause it to malfunction.
- A faulty PCM or programming issues, which can trigger the P1399 code in some cases.
What Tools are Needed to Diagnose
To diagnose the P1399 code issue in your GMC, you need these essential tools:
- A code reader or scan tool to retrieve and display the P1399 code
- A multimeter to measure voltage and resistance in the engine control system
- A wiring diagram to trace the circuit and identify potential issues
- A vacuum gauge to test engine vacuum levels
- A fuel pressure gauge to monitor fuel system performance
How to fix Step by Step
Step 1: Retrieve the trouble code using a scan tool to identify the faulty exhaust gas recirculation (EGR) system.
Step 2: Inspect the EGR valve and its electrical connector for signs of corrosion or damage.
Step 3: Replace the faulty components if you find any issues with the EGR valve or its electrical connector.
Step 4: Check the EGR valve's vacuum hose for blockages or kinks, and repair or replace it as needed.
Step 5: Clear the trouble code and test-drive your vehicle to ensure the repair is successful.
What are the Common Diagnosis Mistakes
When dealing with a P1399 GMC trouble code, avoid misdiagnosis to save time and money.
Misdiagnosis can lead to replacing unnecessary parts, which is costly and frustrating.
Common misdiagnosis mistakes include:
- Not checking the basics, like ensuring the gas cap is tight and the fuel level is adequate
- Ignoring other related trouble codes
- Not checking fuel pressure and volume
- Overlooking possible vacuum leaks
- Not consulting the repair manual or online resources for specific troubleshooting guides
What is the Repair Cost
The repair cost for the P1399 GMC trouble code is $300 to $600, depending on the problem.
If it's the sensor, it's $150 to $300 plus labor.
Wiring or connector issues are $100 to $200.
Reprogramming the engine control module adds $100 to $200.
Can I drive safely with this code?
You can still drive safely with the P1399 code, but monitor your vehicle's performance closely for decreased engine performance, poor fuel efficiency, or unusual noises.