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All of this was complicated by the fact that circuit diagram we had, post above, was WRONG.
Well, the diagram you posted was for a 2009. You indicated you have a 2008.
The 2008 starting circuit for the diesel had two versions, an early and a late production, of the starter circuits according to the EVTM. Sounds like you may have had the early production model and didn't realized it until recently. The late-2008 diagram is similar to the 2009 diagram posted but there are some differences (which I haven't dug into).
Here is the complete diagram for 2008 late production F250
This includes important items missing from the ones posted above. This has CDIM located between the battery and the ignition switch. For automatic transmissions it includes the TCM connection to the PCM.
If you are debugging a starting problem using these circuits it is important to know that the PCM controls the cranking process by shifting the yellow wire from +12V to GND as needed.
I thought all late production trucks would have CDIM. Is this not the case?
IIRC, it was required on late 2008 models built to California or green state emissions standards. If your underhood emissions compliance tag says "California", then that's what it has.
Did you find that the the CDIM was working okay and that the problem was downstream at or in the ignition switch?
The truck came from Texas. I think it was first registered there. But I bought used so...
I am curious to know why emissions states care about CDIM. This is purely an anti-theft feature, part of PATS (Passive Anti-theft System). here is a video I just found on PATS in the 2008 F250. He does not include the CDIM in his bench set up. The video is focused on the flashing "lock" dash light whereas the CDIM is the action end of things that actually switch off power to the ignition switch to disable the truck.
I forgot part of your question, yes, it seems the CDIM is functioning as intended.
The ignition switch contacts in START position appear to be faulty. We can see with a DVM that the concats close only for part of the key rotation then often (but not always!) go back open.
where you bring up the CA emissions "Diesel Engine Idle Shutdown" using the CDIM to turn the motor off if left idling too long.
The "out" for our F250 is that the GVRW is less than 14000 lbs, so F250 of that year in CA should be exempt from this.
Anyway... perhaps Ford put the CDIM to dual use? It would be a simple matter to take a PATS device and reprogram it to shut the truck down if left idling.
Now you have me curious. I'll dig out the component location map and try to lay eyes on a CDIM. That'll take a while as the truck lives with my son now. About an hour south of here.
One thing I found one time was if the transmission shift cable was adjusted wrong, the TCM wouldn’t send out the “ok to start” message to the pcm, cluster showed the right gear and no codes, the cable was adjusted basically past park on the transmission (not towards reverse) and required you to pull the shifter just below the park detent for it to start, I believe neutral worked correctly to start.
I found it when using forscan and monitoring all the start condition pids ( don’t t remember the exact ones off hand). If I was in situation I would hook up forscan and monitor the ignition switch in the SJB/BCM, start request in pcm, pats ok to start just to name a few.
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