P0406 – Meaning, Causes, Symptoms, & Fixes

Code P0406 Definition

Exhaust Gas Recirculation Sensor “A” Circuit High

What Does P0406 Mean?

The P0406 code is the result of the exhaust gas circulation (EGR) sensor A having a high circuit voltage. This code is set when the ECM identifies the EGR voltage is higher than the specified range, thus triggering the check engine light to illuminate on the vehicle dashboard.

P0406 Symptoms*

  • Check engine light
  • Increased production of NOx emissions
  • Decreased engine performance
  • Engine stall
  • Engine pinging upon acceleration or higher speeds
  • Lower fuel economy

*No noticeable adverse conditions in some cases

P0406 Causes

  • Faulty EGR valve sensor
  • Open/Shorted EGR sensor circuit
  • Dirty EGR valve
  • Disconnected wiring in EGR circuit

Code P0406 Severity – Moderate

This trouble code will not prevent your vehicle from regular operation. Code P0406 has a variety of symptoms that could prevent your vehicle from running normally or increase the difficulty of driving. If this code persists, your vehicle should be capable of being driven to nearest dealership.

Code P0406 Common Diagnosis Mistakes

Prematurely replacing the EGR valve without visually inspecting the wiring of the EGR sensor circuit for disconnection.

P0406 Diagnosis

  • Tools Needed to Diagnose:

Difficulty of Diagnosis and Repair

  1. Check to see if there are any other codes along with P0406 and clear your Check Engine Light with FIXD.
  2. Check the freeze frame data for the load and associated temperature of your vehicle upon the code being set.
  3. Conduct a visual inspection of the EGR sensor circuit for shorted or disconnected wiring.
  4. Use FIXD to monitor the EGR while your engine is running and under load.
  5. Remove the carbon buildup within the EGR valve, this might be preventing it from opening or closing properly.
  6. If the problem persists, consider replacing the EGR valve.

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Comments 2

James C Bullard

February 17, 2019

Dumb question; This truck has a diesel engine. Do diesels even have an erg valve?


April 24, 2019


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