Dodge Ram P0406: EGR Sensor “A” → Circuit High

P0406 This is the generic OBDII Diagnostic Code.  It refers to the EGR signal.  In this case, it means that the signal coming from the EGR system is higher than the specified range  Since it is a generic code, it has the same meaning for the Dodge Ram As it would for any other vehicle.  

The EGR system allows a certain amount of the Ram’s exhaust to re-enter the combustion chamber, which helps lower the emissions coming from your Ram’s exhaust.  When the EGR system has an issue, usually the only thing you’ll notice is the check engine light.  

P0406:  EGR Sensor “A” → Circuit High

P0406 Symptoms:  Dodge Ram

Since the EGR valve is part of the emissions system, there aren’t always symptoms associated with P0406 (other than the service engine soon light).  

These are some of the symptoms that are most commonly associated with P0406 if they're present.

• The engine can be slowed or raked.
• Check engine light
• Higher combustion temp
• Emissions have increased

P0406 Causes:  Dodge Ram

P0406 can almost always be caused either by wiring issues, or a defective EGR Valve.  We’ll go over both of them in better detail directly below.

Bad EGR Valve

You can use a scan tool to tell the EGR valve that it is open if you have one.  The EGR valve may not open if it is refusing to do so, you should check the wiring harness for any voltage that runs to the EGR.  The EGR valve can be replaced if the voltage reading is acceptable.  There’s plenty on testing this wiring in the next section.

CarbonEGR circuits can be stuck by junk and even ice.  P0406 most often occurs due to the EGR Valve.  It is possible to save money by replacing the EGR valve without first testing.

If the EGR valve is installed, They are very affordable.  

Problems with Wiring

The wiring harness is a great place to begin diagnosing the problem with P0406 on your Ram.  It is the most common problem because the wiring harness to the EGR is located by the hot engine.

Locate the EGR valve where the wiring harness begins.  Are there visible damage signs on the plugin?  If it doesn’t, go ahead and inspect the wiring harness for any damage.  You’ll be looking for frayed wiring.  It is important to inspect every place it touches the engine or frame.

To check the voltage at the harness, you’ll need a volt meter.  The voltage at the reference Circuit should be checked.  If it’s at 5 volts, but the EGR Valve won’t open, that’s a pretty good indication that the EGR is bad. 

It is a sign of a problem with your wiring if you receive 12 volts instead of 0 voltages.  Here’s a great writeup on diagnosing your wiring issues Source: AA1Car.com

Conclusion

Most of the time, when P0406 is thrown, it’ll be the EGR valve that is the cause.  However, it is still recommended to check the wiring and test it before purchasing a replacement. 

Please leave comments below if you have any suggestions.  We wish you all the best in diagnosing your Ram