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Discussion Starter · #1 ·
I have a 99 Powerstroke in an F450

No Start
No Glow Plug light
No Tach
No check engine light flash
No code reader communication to PCM (data link does have 12V)
PCM 12V at pins 71 and 97
PCM ground at pins 25, 51, 77, 103
PCM relay receives 12V and gives 12V
IDM relay does not come on due to no ground signal from PCM (will worked when jumpered)

My initital diagnosis was the PCM. I sent it to AES module repair. Got the PCM back and having all the same conditions. They said it might be the IDM but after reading the wiring diagram of the PCM and components it doesn't seem likely. Anyone have a similar experience? Did they just not rebuild the PCM correctly?
 

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Discussion Starter · #3 ·
update

So I pulled the 42 way connector and low and behold the wait to start light came on and the code reader has connection with the PCM.

The MAP and EBP were already unplugged.
I unplugged the CPS and plugged the 42 way connector back in.
Got a wait to start and code reader connectivity.

Must the CPS right? Well whether the CPS is plugged in or not, if I crank and then try to restart the key, the PCM goes back to the way it was (no WTS no code reader). Then if I unplug the 42 way connector and try again everything is back to normal. I go to crank and it happens again.

I also am getting a little buzz from something (relay?) under the dash for a couple seconds before the WTS light comes on every time the key goes from off to the ignition on position.

To note, the batteries I am using are very dead even though I charged them. I'm gonna charge another pair and try again.

New symptoms ring any bells?
 

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You may have a short in 5V VREF circuit that the PCM generates either to ground or to another circuit. The Vref circuit powers the sensors to send a signal back to the PCM. If that's shorted out, the truck will NOT start. You may have to get out the multimeter to check. Unplug all the sensors and the 42 pin harness and check the circuit resistance to ground on the engine and against every other wire in the engine harness bundle. If you find anything with less than infinite resistance, you have your work cut out for you tracking down the problem in the harness. Vref should be the brown/white wire (pin 21 on the 42 pin connector). Can you get it to read any codes at all?
 

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Discussion Starter · #5 ·
I got the truck running but didn't really fix anything. I plugged in the 42 way connector and the computer didn't work. I then unplugged each sensor and after I unplugged the IPR the computer came back on. I started plugging sensors back in and the computer worked even after the IPR was plugged back in. So I cranked it and it started and ran as usual. I'm pretty sure there's a short or something that got bumped when I was plugging sensors in and out but I still don't know where.

Also to note, my 42 way connector 10mm bolt is stripped and won't tighten the harness. Since pulling the harness out changes whether the computer works or not it seems like the connectivity is ok when it's plugged in.
 

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I'm pretty sure there's a short or something that got bumped when I was plugging sensors in and out but I still don't know where.
I'd bet the farm on that.

The trick to troubleshooting that kind of stuff is to change ONE thing, Test, change another ONE thing, Test, etc, etc, etc.

Hope it either stays running or you can track down the issue.
 

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Next time this happens and it likely will.. mess with one, test, mess with the next and keep going until you know which it is.
 

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Discussion Starter · #8 ·
Yeah, I did do that. When it wasn't working I unplugged each sensor one at a time until it worked again (IPR being the culprit).

Then I did it in reverse order plugging them in one at a time. But of course plugging in the IPR didn't make it not work again, so it must be something in that area but not the sensor itself.

Thanks for the feedback, all the forums on this subject have been helpful to getting to the point where it works again.
 
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