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i have 03 jeep grand cherokee intermittenly cuts out. I took for drive with scan tool and loses communications when cuts out checked powers and grounds to pcm never lost either so i suspected pcm. replaced pcm test drove cut out again watching scan tool i noticed all modules are showing 13.67 volts with engine running except for bcm. bcm voltage showing 11.2 volts and dropping .when i checked power coming into fuse block i have 13.67. my question is? is the bcm part of the inside junction block and has anybody ran into lower voltage on one module than the others

It's possible. Which engine does this have? Can you check power right at the bcm?

The BCM does unbolt from the JB.

when cuts out voltage is down below 10 volts. the wiring diagram only show power coming into interior junction. this block has bcm right on the back and looks like whole assembly. in know newer chryslers have what the call tipm's which have intergrated modules in the fuse block 4.0 liter power at fuses 13.67

I'd get in there and unbolt that bcm. You might find corrosion there where it plugs into the JB. Any sign of a water leak?

no sign of corrosion on either side of bcm one side with connectors supplys grounds and outputs connector that bolts into junction block supplys power and inputs. is there and way to verify powers is coming from block to bcm i have it at the fuses

The power side is faced against the JB, right? If it is, it's awful tough to verify.

how about corrosion on the mounting side of the BCM. Isn't that what controls ground to the PCM and TCM etc...? There has to be miscommunication somewhere, normally ground or high resistance. What's the condition of your battery (cca volts soc soh), cables, all fuses and all pins on PCM and BCM side? all of this must be checked before condemning. Also, don't forget your diagrams, find out what pins ground your PCM on both plugs. If you supplied the vehicle with aftermarket PCM, that could be the whole issue.

yank the power distribution box and have a look see under it. an easy way is to look at the fuses. if it looks like there is melting around them then you've found your issue. another thing i ran up against once and it was a real head banger was the secondary cable coming off the cable end was corroded internally. grab it where it goes into the lug and wiggle it. you may see corrosion coming out. this also sounds like an issue that would come from a wire piercing from some butt head and it wasn't sealed. i would look along all the wires for the "bump" or what i refer to as the "wire zit". i've also had my fair share of issues with the ignition switch. pull the cover and look for any discoloration at the plug or the back of the switch. i'll also take this time to repeat my obvious offenders, remote start and alarm system.......