Rod do you know if the PCM grounds the 4 02 heater pins when the ECT reads cold and removes the ground when the ECT reads hot? I presume those pins are not grounded all the time, or are they?

 

I don't find anything that explicitly states, but the purpose of the heaters is to get the sensors up to operating temperature quickly (when the older vehicles would have been in open loop). There'd really not be a need for the O2 heaters to be powered/grounded once the exhaust is up to temperature. The troubleshooting manual instructs the technician to check for continuity to the PCM, not to check for ground reference.

-Rod

 

Yeah it makes sense to check the wiring. I was thinking if the 4 pins are permanently grounded theres no way the PCM could be bad, but if the PCM turns the heaters on & off it could be a bad PCM.

It will be interesting to see what ojh finds on this.

 

I replaced the PCM. It started and runs without faults but from what I read it'll take a while, maybe 20 minutes of driving time?
I'm hopeful. I took apart another large connector, applied a light coat of dielectric grease to the pins then plugged & unplugged it 2-3times before tightening the bolt. There's a big one at the transmission I should exercise too.

 

I'm not sure how long it takes for a detected fault to turn into a CEL, and if your new PCM has solved the problem we may never know.

Thanks for the update and hopefully your problem is solved.

 

Well, it did't take long at all for the 'check engine' light to pop on. So much for an easy fix, I'm going to have to put my electricians' hat on and dig into this thing.
On the bright side, I now have a 'good' spare PCM with my VIN# and everything all ready to go when I need it!
I am so swamped with work it is liable to be weeks before I get to it. I will let you know what I find. Thanks for all the help and encouragement.

 

Well that sucks, did you ever verify that you are getting the 12 volts at fuse 11 etc. and are you still getting the same 4 trouble codes.

The PCM is'nt seeing the 12 volts on any off the 4 pins so like Rod said it must be a wiring problem

 

And in the laughter is the best medicine dept. do a google search on "school answering machine" and have a good laugh courtesy of out friends in Australia. It's 1 minute and 50 seconds.

 

One other thought, since the PCM is new you might get a trouble code P1000, which simply means the truck needs to be driven normally for a couple days to reset the diagnostic monitors.

 

Nice thought. I just went and checked, the codes are the same as recorded in Post #9.

 

Bummer, if you can figure out where the missing 12 volts is going this problem will go away. Keep us posted & good luck with it.

 

Whelp, I got good news! I dug out the old flux capacitor resistan-o-meter and discovered the counter rotational dinglearm was causing irregularities in the flux field - we all know happens then, the inverse parameter switch just got hung up and couldn't release!
In reality, you guys were right all along. It was the fuse. The 02 heater circuits are fuse #11, and I checked #11 a dozen times. Except, there is a difference between Maxi fuse #11 and mini fuse# 11! In that little fuse box they have duplicate numbers and distinguish between them by calling it 'Maxi' fuse or 'Mini' fuse.
The PO had added circuits to the truck, they had snagged a wire into mini fuse #11 and it ran to a box for employees to fill it at the pump with their badges, they had a reciever & transmitter connected to that circuit. I pulled all the wires, boxes and fuse not even thinking the circuit actually supplied something on the truck. I thought I was cleaning up some creative wiring.
It is back to running sweet as ever again. Time for some shocks, lets see if I screw that up.
thanks for all your help!

 

Glad to hear you got it figured out. Hopefully those PCMs were not too pricey.

-Rod

 

If Ford had wired anything else to mini fuse 11 you'd have know right away it was blown. But fixed is good congrats on that