03' 6.0 tech help! no comm. with pcm, no inj. buzz

[ps_lane01]

Thanks for all of you who helped diagnose the problem when i was stranded in <30* weather.. Engine died randomly after no boost no power while driving. Went to start it again and no response from injectors fuel pump etc. tried looking at DTCs with sct tuner and it will not communicate with PCM at all. I figured it might be a neutral safety or transmission range sensor (whatever this truck has) so i unplugged PCM connectors one at a time... With the middle connector unplugged i was able to crank it with injectors, pumps etc but no start. When i was driving i was running a ground switch to the fan clutch because of my plow overheating the truck in the past.. maybe some correlation with the fan clutch being on that middle PCM connector? i have tried everything i could find on the inet to diagnose this problem...

Is there a way to test the PCM harness pins for grounds, resistance, etc? is there a sensor on that connector that will cause the PCM to not communicate with anything? I dont want to apply power or ground to a module or sensor and create more problems.. AND i dont know anyone local with another 6.0 PCM

You guys are amazing and happy new years to ya!


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[ps_lane01]

Bumpity bumpity bump, to the top i jump!

Has anyone experienced something like this or have any ideas?


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[aclem16]

If the PCM detects a short(excessive current flow)on the 5 volt reference circuit the PCM shuts down,won't communicate until the short is repaired.Many components use reference voltage from the PCM.Here's a quick way to see if that might be your problem.Turn the ignition "On" and backprobe the EBP sensor or peel back some insulation on the brown and white wire and check the wire for 5volts.If it's present you need to now check all PCM powers and grounds.If the 5volts is NOT present you need to monitor this wire while unplugging each component that receives 5volt ref. from PCM.Or you can unplug them and see if it will start.Here's a list of things that receive 5volt ref. from PCM:ICP,EBP,MAP,MAF,APP,EGR,BARO,Fan Clutch,and A/C pressure sensor.Good Luck.

[ps_lane01]

Originally Posted by aclem16

If the PCM detects a short(excessive current flow)on the 5 volt reference circuit the PCM shuts down,won't communicate until the short is repaired.Many components use reference voltage from the PCM.Here's a quick way to see if that might be your problem.Turn the ignition "On" and backprobe the EBP sensor or peel back some insulation on the brown and white wire and check the wire for 5volts.If it's present you need to now check all PCM powers and grounds.If the 5volts is NOT present you need to monitor this wire while unplugging each component that receives 5volt ref. from PCM.Or you can unplug them and see if it will start.Here's a list of things that receive 5volt ref. from PCM:ICP,EBP,MAP,MAF,APP,EGR,BARO,Fan Clutch,and A/C pressure sensor.Good Luck.

That is extremely helpful! checked all grounds, powers, vref, ficm pwrs, grnds, etc... Then Swapped it with a different pcm and it started right up. Got a replacement on the way... I learned not to use a ground switch on the a/c clutch to over ride the pcm... Got a "snowplow package" on the way also.


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[ps_lane01]

For future reference- according to the mechanic: ICP shorted internally and EBP sensor went bad so vref did not allow the pcm to communicate until that short was fixed. The PCM also failed while driving and needed to be replaced. Not sure which caused which to happen first. 2200$ and three weeks later and now it runs. Thanks for your help and maybe this will help someone else.


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