Understanding P0406: Exhaust Gas Recirculation Sensor A Circuit Low

Introduction to P0406

What is P0406?

P0406 is a generic OBD-II trouble code indicating a problem with the circuit of the Exhaust Gas Recirculation (EGR) sensor A. The code is usually triggered when the car’s computer, also known as the Powertrain Control Module (PCM), detects a voltage signal from the EGR sensor that’s outside the normal range.

Causes of P0406

This trouble code can be caused by a number of issues, such as a faulty EGR sensor, damaged wiring, or problems in the PCM itself.

Detailed Analysis of P0406

Role of the EGR System in a Vehicle

Function of the EGR Sensor

The EGR system helps to reduce the amount of harmful gases emitted by a vehicle by recirculating a portion of the exhaust gases back into the engine’s combustion chamber. The EGR sensor, specifically, monitors and controls this process.

What Happens When P0406 Error Occurs

Impact on Vehicle Performance

When the P0406 error code is activated, it can lead to a variety of performance issues in the vehicle, such as power loss, reduced fuel efficiency, or increased emissions.

car vertical

Troubleshooting P0406

Symptoms of P0406

Common symptoms of the P0406 code include rough idling, reduced power, increased fuel consumption, and sometimes a Check Engine light.

Diagnosing P0406

Diagnostic Tools

To diagnose this code, you will need a professional OBD-II scanner.

Diagnostic Procedure

The diagnostic process includes checking the EGR valve, wiring, and PCM for faults.

Repairing P0406

Replacement of EGR Sensor

If the EGR sensor is found to be at fault, it will need to be replaced.

Cost Considerations

The cost to replace an EGR sensor can vary depending on the make and model of your vehicle.

Prevention Tips for P0406

Regular maintenance and inspections of the EGR system can help prevent the P0406 code from appearing.


Understanding and fixing the P0406 code is crucial to maintaining the performance and emissions standards of your vehicle. With the right knowledge and tools, it’s a task that can be managed effectively.


  1. What does P0406 mean?
  • P0406 is a specific OBD-II trouble code that indicates a high voltage issue with the circuit of the Exhaust Gas Recirculation (EGR) Sensor A.
  1. What are the symptoms of a P0406 code?
    • Symptoms can include reduced vehicle performance, rough idling, increased fuel consumption, and an illuminated Check Engine light.
  2. How do I fix a P0406 code?
    • Fixing a P0406 code may involve replacing a faulty EGR sensor, repairing damaged wiring, or in some cases, even replacing the PCM.
  3. What causes a P0406 code?
    • The code is typically caused by a faulty EGR sensor, damaged wiring or connectors, or problems with the PCM.
  4. Can I drive my car with a P0406 code?
    • While you might be able to drive your car with a P0406 code, it’s not recommended due to the potential damage to the engine and the environment caused by improper exhaust gas recirculation.