This is on a 98 Explorer with 5.0L engine.
The CEL turned on and I pulled the infamous P0401 code. KOER showed P1408 - EGR flow out of range. I found the DPFE dead, and outputting maximum flow (full voltage) all the time, even with the tubes disconnected. The scanner reports it, and I also measured it directly.
So far so good, but here is the strange thing: when I run KOEO it reports P1409. According to the FSM, P1409 is a regulator circuit failure, and it tells me to check the solenoid resistance, power supply, shorts, opens, etc. Everything is fine, leaving a failure of the driver circuit in the PCM the only option. While it's not impossible, I am finding it unlikely that the PCM has two unrelated problems: not detecting the out of range DPFE reading and not driving the solenoid. Is anyone aware of a TSB or something like that which corrects the interpretation of P1409 in response to the on-demand test. If it were DPFE out of range and not a regulator circuit problem (or possibly either one of the two), everything would make sense.
Thanks,
IK