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Re: 2003 ford expedition check engine light is on. It is...
This DTC says nothing about changing the sensor or the connector or pig tail ! It's a circuit voltage low code P0405 - DPF EGR Sensor Circuit Low Voltage Detected
See DTC P1400
Problem with wiring or PCM ! P1400 - DPF EGR Sensor Circuit Low Voltage Detected
The EGR monitor checks the DPF EGR sensor signal to the PCM for low voltage. The test fails when the average voltage to the PCM drops to a voltage less than the minimum calibrated value.
DPFEGR circuit short to GND
Damaged DPF EGR sensor
VREF short to GND
A DPF EGR PID reading less than 0.2 volt with the key ON and engine OFF or running, indicates a hard fault.
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I'm probably not going to be able to give you a proper diagnosis without knowing which codes are setting the check engine light. There are about 300 problems that can set the light. Most common thing for your vehicle with not running bad is what they call the DPFE (differential pressure feedback) sensor. It's basically a vacuum/pressure monitor for the EGR system and they get stopped up or corrode as they have exhaust gases running through them and are made from aluminum or plastic. If you post code numbers (go to advance or autozone and they will read them for free) and I can give you a better idea of what the problem is.
There could be many issues. These codes read your engine is running too lean. Check : all your vacuum hoses for leaks, PCV valve and hose, MAF sensor. This may require an experienced technician to figure this out. Hopefully I help'd!!
Go to Autozone or Oreillys for a free scan. The "check light" may have diagnosed the problem. Usually it is a TPS -throttle position sensor or some part in the EGR circuit. If it does diagnose "EGR" flow problems you should clean under the airhorn to remove the soot buildup.
Remember to disconnect the battery cable for 10 minutes to clear the trouble codes after working on the truck.