The latest vehicles contain an exhaust gas recirculation (EGR) system to control exhaust gas emissions. The EGR system has an EGR valve. The EGR valve regulates the recirculated exhaust gas. The powertrain control module (PCM) triggers the P0404 code when it monitors an issue with the performance of the EGR sensor A. This article explains the P0406 code causes, symptoms, and fixing.
P0406 Code Definition
P0406 stands for “Exhaust Gas Recirculation Sensor A Circuit High.”
What does the P0406 Code mean?
P0406 code indicates that your powertrain control module (PCM) detects a high voltage signal from the exhaust gas recirculation (EGR) sensor A.
Exhaust gas recirculation (EGR) is an emission control technology used in the latest vehicle models to reduce the emission of NOx.
The main function of the EGR system is to recirculate a definite amount of the exhaust to the combustion chamber to lower exhaust emissions. The emission of nitrogen oxide (NOx) is very hazardous to the environment. Therefore, ERG technology is introduced to control the emission of NOx.
The EGR system is most commonly used in diesel engines. The performance of the EGR system is observed by the powertrain control module (PCM).
Your PCM sets the diagnostic trouble code (DTC) P0406 code when it detects the voltage signal coming from EGR sensor A is higher than the preprogrammed range.
Causes of the P0406 Code
The P0406 engine code is triggered due to one or more of the following causes:
- Faulty EGR valve
- Excessive carbon buildup in the EGR valve
- Carbon buildup in the EGR sensor
- Open/short EGR sensor circuit
- Poor electrical connections
- Damaged or corroded wiring to the EGR valve
- EGR valve vacuum line leaks
- Clogged EGR passages
Symptoms of the P0406 Code
- Check engine light is flashing
- Rough idling
- Your vehicle is unable to pass the emission test because of increased NOx emissions
- A reduction in the engine performance
- Engine stalling
- Engine knocking
- Poor fuel economy
Read More: EGR Valve Parts and Function
How to Diagnose the P0406 Code
Follow the following steps to diagnose the P0406 code:
- Use an OBD-II scanner to check the PCM history, pending and existing codes
- Note the freeze frame data, such as vehicle load, run time, and temperature when the trouble code triggered
- Clear the PCM memory to clear the codes and perform a test drive. If the P0406 code returns, then perform further inspection to find the root cause of the problem.
- Visually inspect the connections and wires to the EGR system. Check for exposed wiring, loose connections, or damaged wires.
- Inspect the vacuum lines for a leak.
- Test the EGR position sensor by using a multimeter. Compare the multimeter readings with the readings written on the vehicle’s service manual.
- Inspect your EGR valve for carbon accumulation. If your EGR valve is clogged, remove it and clean it properly.
- Visually inspect the EGR sensor and EGR valve for damage.
- Inspect the PCM of your vehicle.
- Clear the trouble codes using an OBD-II scanner and perform a test drive.
Common P0406 Code Diagnostic mistakes
- Not properly inspecting all the parts
- Nor inspecting the wiring and connections
- Replacing the EGR sensor or EGR valve without inspecting the wiring and connections
- Replacing the unnecessary components
- Replacing the EGR valve without inspecting the vacuum system for leaks
- Installing the new EGR parts without testing them
P0406 Code Repair Cost
The P0406 code fixing or repairing cost depends on the nature of the repair. To fix this code, you need one of the below-given repairs:
| Parts | Cost |
| Vacuum leak repair | $90 to $220 |
| EGR valve replacement | $220 to $370 |
| MAF sensor replacement | $180 to $520 |
| EGR temperature sensor replacement | $210 to $240 |
| EGR pressure sensor replacement | $90 to $130 |
What repairs can fix the P0406 Code?
To fix the P0406 code, you need one or more of the following repairs:
- Clear the trouble codes and perform a test drive
- Repair or replace the damaged wires and connections
- Fix the vacuum leaks
- Replace the bad EGR valve
- Clean the carbon buildup in the EGR passages
- Replace the bad EGR pressure sensor
- Replace the faulty EGR position sensor
- Replace the faulty PCM
FAQ Section
How serious is the P0406 code?
The P0406 code is not a serious trouble code. This trouble code indicates an issue with your EGR valve. A faulty EGR valve may increase exhaust emissions. Exhaust gases are very harmful to the atmosphere. It may also lead to the failure of the engine’s internal parts. Therefore, you should fix the P0406 code as soon as possible.
Can a bad EGR position sensor cause P0406 code?
Yes, a bad EGR position sensor is one of the major causes of the P0406 code. An issue with the EGR position sensor (i.e., a short or high resistance in the sensor circuit) may lead to the high voltage condition indicated by the P0406 code.
Can I drive with code P0406?
Yes, you can drive with the P0406 code. But it is not recommended to drive with this code for a long time. This code indicates an issue with your EGR valve. A faulty EGR valve may damage the internal parts of the engine.
Can Carbon buildup in the EGR valve cause P0406 code?
Yes, the buildup of the carbon in the EGR valve affects its performance and causes the P0406 code.