Q: I have a 2005 Chrysler Town and Country Touring with 3.8 liter V-6. I just saw the “check engine” light come on, and the scan-tool code is P0406. From what I’ve seen on the Web, there is 98 percent probability that it’s the exhaust gas recirculation valve. Looks like I can replace it myself, but is there a way I can confirm the bad part before investing $60-$100 for the part? My scan tool is a basic, not Chrysler-specific.

— Jim Cauble

A: Jim, it’s neat to see folks communicating with their cars and trucks as you have.

Diagnostic trouble code P0406 indicates the EGR valve position sensor voltage is abnormally high. The sensor receives five volts from the engine control computer and returns a portion of this voltage depending on pintle, or valve plunger, position. The feedback voltage varies from high to low as the valve transitions from closed to open. An abnormally high voltage can result from the valve failing to open or move properly, a faulty position sensor, or a wiring fault.

According to Identifix, a highly useful professional information database, about 95 percent of the time, renewal of the Town and Country EGR fixes the P0406 trouble code. What seems to happen most is a fault within the feedback sensor, or the valve fails to move as it should. To really be sure of the exact cause of the fault, a professional grade scan tool is needed to command the valve while observing position sensor signals. If the valve fails to move, steps are taken to determine the cause. If the valve moves (engine idle becomes very rough), but the sensor voltage remains high, tests are run to determine if the cause is the sensor or circuit.

I normally cringe at the thought of throwing parts at a car because of a trouble code, but in this case it seems reasonable. Before ordering a replacement EGR valve, check the electrical connector of the existing one for looseness or corrosion. And if renewing the part, be sure to use a high-quality, snug-fitting 8mm socket, as the bolt heads are easy to round off.