Intersting problem. 2002 escape V6 had CEL on, drove it like that for years (VERY DUMB). Car lost power, blew out cats and melted DPFE.

Replaced cats and DPFE, CEL still on. Code P0402 (excessive EGR)
Then replaced EGR valve, EGR solenoid. Still got P0402.

Did voltage test on DPFE. Probed the SIG wire with KOEO (key on engine off), got ~1 volt (normal). Then start car, get 4.5V (should still be 1V).
So I disconnected DPFE from EGR tubing, and still get 4.5 V, so this tells me there is an electrical problem rather than actual EGR flow.

Next still with KOEO and sensor removed from tubing, Applied vacuum to the downstream port, watched the voltage climb up to 4.5V with increasing vacuum, like it should. This says DPFE is working properly, in theory.

So now I'm thinking there's a wiring problem. Like a short between VREF and SIG. Since the DPFE gives the correct voltage with KOEO, but not with engine on, I'm thinking that rather than a short between the two wires maybe this is a PCM problem?

So I completely remove DPFE and I probe the SIG wire and get +5V at both KOEO and with engine running. But with the sensor attached, at SIG I get +1V with KOEO, and +4.5V with engine on.

I'm thinking of trying yet another DPFE sensor, but I suspect this will not fix the problem. Does anybody have any insight?

Thanks,

Joe

 

get a vacuum gauge and check your engine vacuum since that's the thing that's "driving" the sensor. Sounds like you might have a vacuum leak.

 

Hey bud, thanks for the reply.
Problem is fixed.
It wasn't a vacuum problem. When I disconnected the vacuum line to the EGR I was still getting 5v with the EGR valve completely closed. So I new I either had a sensor problem or a wiring/PCM problem. So I traded in for a new DPFE sensor (even exchange, no cost), which then melted off again!

I relented and took it to Ford, which charged me $92 to "diagnose" the problem. They said it was the DPFE wiring harness and sensor (which had melted). They wanted to replace the sensor as well as the whole wiring harness (which was a little melted but still functional) and charge me $380!!!! And then he said he wasn't sure that would fix the problem, but we had to do that before further diagnosis could be done! This was starting to get really expensive. Well after spending roughly $1700 on cats I wasn't thrilled with this. I asked why he thought the harness was bad. He couldn't verbalize this to me. I said in my mind there are only two reasons to replace wiring. Either the wires are broken or they are shorted. He said he thought neither were the case. He didn't even say whether my PCM was functioning correctly, which I told him was basically what I was wanting to know. So I said thanks (for nothing) and paid the $92 (waste of money). Now back to square one. I started to wonder whether the aftermarket sensor was the reason for the weird voltages. I figured trying an OEM sensor was cheaper than a new PCM, or than Ford's $380 cost to replace a functioning wiring harness. So I turned around and went to their parts counter to get an OEM DPFE sensor for $75. Well, this fixed the problem! I was getting the correct voltages then, and no more problems now. The aftermarket sensor I got from Advance auto was a piece of junk!! My amateur explaination is that the junk sensor was sending out 5v, telling the system that the EGR was open inappropriately. Consequently, a signal was sent to keep the EGR closed. Since the EGR would never open, the exhaust gas got hotter, which then melted the sensor.

So, after wasting $92 at ford for a non-diagnosis, and weeks of headaches and a non-working escape, problem fixed.

This reaffirmed my position of avoiding dealer auto mechanics (it was a moment of weakness and WILL NOT happen again).

Lessons to be learned are:

1. Don't ignore your CEL lest ye waste hundreds on catalytic converters.
2. Beware dealer mechanics - you are smart enough to figure out plenty for a lot less money! I saved over $200 by not listening to them (even with wasting $92 by going to them in the first place - so i could've saved $300 by NOT!)
3. If you have replaced parts and things still aren't functioning right, start suspecting the NEW part!
4. BEWARE AFTERMARKET DPFE SENSORS!! (and other aftermarket parts for that matter). Sometimes the extra cost of OEM parts is money well spent.

I hope this information helps someone.