Technical Definition:

Exhaust Gas Recirculation (EGR) (Sensor A) Circuit High

Trouble Code: P0406
Address: 0x0406
System: Powertrain
Subsystem: Auxiliary Emission Controls
Technical Description:

Possible Causes:
  • EGR sensor signal circuit shorted to B+ (battery voltage)
  • EGR sensor signal circuit shorted to the 5 volt reference circuit to EGR
  • EGR sensor ground circuit open
  • EGR sensor signal circuit open
  • Bad EGR (internal failure on EGR sensor or solenoid)
  • Debris caught in valve and holding it open or closed

Possible Symptoms:
  • Increase in combustion temperatures (and NOx emissions)
  • MIL (Malfunction indicator lamp) illumination
  • Possible surging while driving
  • Possible intermittent stall

Possible Solutions:

If the vehicle starts and stalls or will not run with this code present, try unplugging the EGR valve and then restarting. If this makes no difference, remove the EGR valve and inspect for debris. Clean and reinstall. If this still doesn’t fix the problem, block off EGR port and attempt to start the engine. If this allows the engine to start, the EGR valve is stuck open and needs replaced. If unplugging the PCM controlled EGR valve allowed the engine to restart then there is likely a wiring problem, possibly a short holding a solenoid open.

Using a scan tool, view the EGR position on the datastream with the Key on Engine running and compare with the EGR desired position. If it reads normal, suspect an intermittent problem. If it shows 5 volts or higher, check the EGR sensor signal circuit for a short to the 5 volt reference wire or to B+. Repair as needed. Also check that there is a good ground path on the ground circuit. Repair any opens or shorts on ground circuit

On a vacuum controlled EGR valve with EGR solenoid: if unplugging the EGR valve vacuum source allows the engine to start, then suspect a bad EGR solenoid allowing vacuum to the EGR valve all the time. Replace the EGR solenoid as needed. If this code is present and your engine starts and runs just fine, suspect an open in the wiring. Inspect and repair any wiring problems. If the wiring checks out, replace the EGR valve. If the wiring to and from the EGR valve

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