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P0406 OBD-II Trouble Code: Exhaust Gas Recirculation Sensor "A" Circuit High

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P0406 code definition

P0406 is a general ODB2 trouble code indicating a fault within the exhaust gas recirculation EGR circuit. This code is similar to P0400, P0401, P0402, P0403, P0404, P0405, P0407, P0408, P0409.

What the P0406 code means

P0406 means that the exhaust gas recirculation (EGR) sensor A has high circuit voltage. The ECU detects this high voltage and sets a Check Engine Light. The Check Engine Light will be illuminated on the dashboard.

What causes the P0406 code?

  • Failed EGR valve
  • Excessive carbon buildup
  • Open or short in the wiring harness
  • Poor electrical connection
  • Leak in the vacuum line to EGR valve

What are the symptoms of the P0406 code?

  • In most circumstances the driver may not notice any symptoms other that then illuminated Check Engine Light.

  • Some vehicles may have a slight engine hesitation and fluctuating RPMs.

  • In rare cases the vehicle may have some pinging at higher load and engine stalling.

How does a mechanic diagnose the P0406 code?

  • Uses a scan tool to check for any history, pending and current codes

  • Notes freeze frame data, such as vehicle temperature, run time, and load when the fault occurred

  • Clears the code

  • Performs a test drive trying to duplicate the conditions from the freeze frame data

  • Performs a visual inspection for damaged or worn wiring, broken vacuum lines, and loose electrical connectors

  • Uses the scan tool to view EGR position upon startup and running and manifold pressure

  • Inspects EGR valve for carbon buildup causing it to not open and close properly

Common mistakes when diagnosing the P0406 code

Diagnosis of the P0406 code can be a simple matter or turn into a nightmare if step by step diagnosis is not performed and every step needed completed. This can cause the real problem to be over looked and unneeded repairs performed.

How serious is the P0406 code?

P0406 has a wide range of symptoms that can vary from just the Check Engine Light being on to a vehicle that won't stay running or drives poorly. In vehicles with drivability concerns care should be taken when driving.

The P0406 code should not prevent the vehicle from being driven to a safe location after the fault occurs.

What repairs can fix the P0406 code?

  • Replacing the EGR valve
  • Repairing or replacing wiring harness as needed
  • Repairing poor electrical connections
  • Replacing the vacuum line
  • Cleaning excessive carbon buildup

Additional comments for consideration regarding the P0406 code

In some cases the EGR valve and system may be able to be cleaned. There are specialized cleaners that are used to break up the carbon so it can be cleaned.

Cleaner instructions must be followed but some EGR valves may be able to have the carbon removed and work properly instead of needing replacement.

Need help with a P0406 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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