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

P0406 It is an OBDII diagnostic code.  This code deals with signals coming from EGR systems.  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 Escape As it would for any other vehicle.  

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

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).  

Below are the top symptoms of P0406 that can be found when they occur:

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

P0406 Causes:  Ford Escape

P0406 can almost always be traced to wiring or EGR Valve problems.  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.  It is possible to replace the EGR valve if it's OK.  There’s plenty on testing this wiring in the next section.

CarbonThe EGR circuit can become stuck from junk or ice, as well as other substances.  P0406 can be caused by the EGR valve.  It is possible to save money by replacing the EGR valve without first testing.

If the EGR valve is installed, These are quite affordable.  

Problems with Wiring

You can start to diagnose P0406 problems in Escape's wiring harness.  It is more likely that it is because the EGR valve wiring harness 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.  You should inspect any area where it comes in contact with the frame or engine.

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 Source: AA1Car.com

Conclusion

Most of the time, when P0406 is thrown, it’ll be the EGR valve that is the cause.  But it's still worth checking the wiring and testing it before you buy a new one. 

Please leave comments below if you have any suggestions.  Good luck diagnosing your Escape!