Ford Ranger P0406: EGR Sensor “A” → Circuit High

P0406 It is an 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 Ford Ranger As it would for any other vehicle.  

The EGR system allows a certain amount of the Ranger’s exhaust to re-enter the combustion chamber, which helps lower the emissions coming from your Ranger’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:  Ford Ranger

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.

• Engine surging and/or stalling
• Check engine light
• Higher combustion temperature
• Emissions have increased

P0406 Causes:  Ford Ranger

Most of the time P0406 can be explained by bad EGR Valve or wiring.  We’ll go over both of them in better detail directly below.

Valve for EGR - Bad

A good scanner tool can be used to force the EGR to open.  It is worth checking the wiring harness to make sure the EGR valve opens.  It is possible to replace the EGR valve if it's OK.  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.  Blindly replacing it without testing can lead to a costly repair.

It could be the EGR valve. These are quite affordable.  

The Wiring of Issues

The wiring harness is a great place to begin diagnosing the problem.  The wiring harness connecting to the EGR valve in your Ranger is the most likely to be the cause of the problem.

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. 

A wiring problem is indicated if you have 12 volts and 0 volts.  Here’s a great writeup on diagnosing your wiring issues From 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.  Good luck diagnosing your Ranger!