Cold Codes: P0406

I've been working with trouble codes and self-diagnostic systems since.. well, since they became part of car repair. The earliest systems were very different than OBDII. With OBDII there are more standardized aspects to testing. For instance, generic OBDII trouble codes all mean the same thing no matter the manufacturer. A P0406 breaks down to, P=Powertrain, 0=Generic, 4=Auxilary Emissions. The last two digits, 06 define the problem; EGR Position Sensor Circuit High. Notice that it does not say the problem is a bad EGR valve, a bad PCM, or anything about what is needed to repair the problem. The PCM uses a voltage signal output from the EGR position sensor to verify EGR valve operation. The code description is saying that there is a problem with the sensor voltage on that circuit. I will step back just a bit more, it is saying that there MAY be a problem with the sensor voltage on that circuit. Finding why the code set instead of what the code is, that is where actual diagnostics begin. The code P0406 means the same for each manufacturer but the system in place for EGR sensor monitoring would likely be different, which would make the testing different. The next step would be to verify the problem. 

A 2011 Jeep Wrangler, 4x4 3.8:

On the Jeep you would need to monitor the sensor signal looking for not only the correct voltage while commanding EGR but looking with a scope for a clean signal. From that point, you go where your testing takes you. I will say that on the Jeep it is indeed usually a bad EGR position sensor, which is part and parcel with the valve itself. 

On other makes the wiring would vary but you would still be looking for the EGR position signal and for a problem with that signal. 

2005 Impala:

On the Impala the sensor is usually fine but the EGR valve is sticking. Still, both parts are made together. Do the testing and know what you need. Always remember that a trouble code is there to steer you to the system where a problem may be. It isn't there to tell you what you need to fix the problem. 

Thanks

Kenny@ggauto.repair