#2 Diode to PCM Mr. Mike T. Please help - F150online Forums

#2 Diode to PCM Mr. Mike T. Please help

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Old 11-01-2001, 08:40 AM
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Join Date: Jun 2001
Location: Henderson Nv. USA
Vehicle: 1997 Ford F-150
Posts: 51
Unhappy #2 Diode to PCM Mr. Mike T. Please help

Hello to you all.
Mike can you help me please, infact does anyone know why my
#2 Diode for the PCM blows out on me. Which is located in the power distribution box. I mean all that is left is the 2 spades and then the engine does not run of coarse.
This is the second time. The first time it had blown right out and I replaced it and I checked it last night by changew and all the black plastic has been burnt off of the diode exposing the inside ( looks like a transistor or something) but it hasn't lost contact yet.
What is the purpose of this diode?
Would the chip be causing the problem?
Need help soon don't want truck to burn up, Greatly Appreciated
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Old 11-01-2001, 06:20 PM
JMC JMC is offline
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Join Date: Dec 1997
Location: Windsor,Ontario,Canada
Vehicle: 2000 Ford F-150 4x4
Posts: 9,398

The #2 diode stops current from flowing backwards fron the PCM Power Relay to the Ignition coils. If you are continiously blowing this Diode I would look at the PCM power relay. Replace it with a known good one and see if the diode blows. I suspect the relay is shorted to ground and blowing the Diode.


Jean Marc Chartier
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Old 11-04-2001, 03:13 PM
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Join Date: Mar 1998
Location: Virginia
Vehicle: 2001 Ford F-150 SVT
Posts: 13,385
Hi Jim,

As we have discussed with you previously, this has nothing to do with your Superchip. If that diode blows 15 times more in the future (heaven forbid!!), it will still have nothing to do with your Superchip, my friend.

I would suggest checking out the information & advice kindly offered by JMC in this regard in an attempt to get to the actual underlying problem, which has nothing to do with the Superchip itself.

Speaking of JMC, many thanks to JMC for his specific response, & we hope that leads you on your way to getting this diode-busting problem solved permanently. Please do let us know what happens when you follow up on this Jim.

Good luck!
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Old 11-07-2001, 09:55 AM
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Join Date: Jun 2001
Location: Henderson Nv. USA
Vehicle: 1997 Ford F-150
Posts: 51
Thanks to both of you I think that changing the PMC relay will work. What's so strange was that the diode didn't just blow and that was it but on 2 different occasions it slowly melted away and disconnected when there was just the 2 spades left.
Thanks again guys I'll let you know if it acts up anymore. Jim
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