PROBLEM SOLVED (was: no bus / CCD message or How to display error / fault codes 2001 Dodge Ram?)

From : maxpower

Q: first let me thank maxpower aka glenn measley miles fmb nosey tbone tom lawrence and joe brophy for the wealth of information and the detailed answers to my technical questions about the chrysler data bus tmc. my special thanks to glen for giving me the encouragment to continue diagnosing this problem in my own driveway. gee thanks but i didnt encourage you to work on it!! but im glad you got it fixed. i still think it is rain related. also i wont to say that i am one of those so called monkeys at the dealer let me know when you have another problem!! to recap 2001 dodge ram short cab 5.2l 2wd all options. truck ran fine one day was parked overnight there was rain that day and night then the next morning engine would turn over but not start. after 2 days and some poking around disconnecting/reconnecting various connectors engine would start and briefly the guages worked for about a minute then went dead but engine could then be started at will after that. when ignition is switched to on odometer displays no bus and the overhead console displays ccd. not having a proper wiring diagram i focused on the wiring to the instrument cluster mic. there are 2 connectors 10 pins each and after identifying all the ground and power pins there were about 6 pins that were candidates for being the bus. one of those pins was showing 40 ohms to ground which i thought was strange. i metered each of those 6 to the 3 connectors at the pcm and found that only 2 of them did indeed go to the pcm. as i suspected from examining much of the dashboard wiring those wires are always a twisted pair - indicative of some sort of differential signaling and i suspected they were indeed the bus. one of those wires was the one showing 40 ohms to ground and now i see its showing 40 ohms to a third pin at the pcm on a different connector. ok so what i do next is this with the 3 connectors at the pcm already off i disconnect as much of that cable as possible. that basically means to disconnect its opposite end from the main fuse module beside the battery its a big square connector with a hold-down bolt in the middle. ok im still reading 40 ohms - so whats going on under the truck i disconnect a cable going to the transmission its got maybe 10 wires and discover that one of those wires is the one making a 40-ohm connection to one of the bus wires this is with all connectors still disconnected. ok time to cut the main cable away from the firewall and remove all the black tape and physically inspect the twisted-pair bus wires. i do this all the way to the connector at the fuse module and still get 40 ohms. the last thing is to take apart the square fuse-module connector. i do this and as i manipulate the outer cover the 40-ohm connection goes away. i manipulate the wires and manage to make the 40-ohm connection come and go. i look closely at where the bus wires go inside this connector and where the mystery wire to the transmission goes and it turns out theyre right beside each other. but whats really wierd is that theres no indication that theyre touching. no corrosion no chafing no bared insulation. very strange. so i re-position the wires and close up and re-tape the connector then re-tape the entire main cable back to the pcm connectors and re-install all connectors and assemblies in the dash that i took apart. needless to say the mic worked fine and no pcm or mic codes were displayed when i tried the various diagnostic code reporting methods. im thinking that this problem had nothing to do with the rain that happened the night before this problem started but i still dont know why the engine wouldnt start during the early phase of this situation. im glad i did this and not simply take it to the dealership and maybe those monkeys wiggle something and the problem goes away only to come back later. at least now i know where to look if it happens again. .

Replies:

From : joe brophy

on mon 07 aug 2006 040911 gmt mopar man mopar@man.com wrote first let me thank maxpower aka glenn measley miles fmb nosey tbone tom lawrence and joe brophy for the wealth of information and the detailed answers to my technical questions about the chrysler data bus tmc. my special thanks to glen for giving me the encouragment to continue diagnosing this problem in my own driveway. to recap 2001 dodge ram short cab 5.2l 2wd all options. truck ran fine one day was parked overnight there was rain that day and night then the next morning engine would turn over but not start. after 2 days and some poking around disconnecting/reconnecting various connectors engine would start and briefly the guages worked for about a minute then went dead but engine could then be started at will after that. when ignition is switched to on odometer displays no bus and the overhead console displays ccd. not having a proper wiring diagram i focused on the wiring to the instrument cluster mic. there are 2 connectors 10 pins each and after identifying all the ground and power pins there were about 6 pins that were candidates for being the bus. one of those pins was showing 40 ohms to ground which i thought was strange. i metered each of those 6 to the 3 connectors at the pcm and found that only 2 of them did indeed go to the pcm. as i suspected from examining much of the dashboard wiring those wires are always a twisted pair - indicative of some sort of differential signaling and i suspected they were indeed the bus. one of those wires was the one showing 40 ohms to ground and now i see its showing 40 ohms to a third pin at the pcm on a different connector. ok so what i do next is this with the 3 connectors at the pcm already off i disconnect as much of that cable as possible. that basically means to disconnect its opposite end from the main fuse module beside the battery its a big square connector with a hold-down bolt in the middle. ok im still reading 40 ohms - so whats going on under the truck i disconnect a cable going to the transmission its got maybe 10 wires and discover that one of those wires is the one making a 40-ohm connection to one of the bus wires this is with all connectors still disconnected. ok time to cut the main cable away from the firewall and remove all the black tape and physically inspect the twisted-pair bus wires. i do this all the way to the connector at the fuse module and still get 40 ohms. the last thing is to take apart the square fuse-module connector. i do this and as i manipulate the outer cover the 40-ohm connection goes away. i manipulate the wires and manage to make the 40-ohm connection come and go. i look closely at where the bus wires go inside this connector and where the mystery wire to the transmission goes and it turns out theyre right beside each other. but whats really wierd is that theres no indication that theyre touching. no corrosion no chafing no bared insulation. very strange. so i re-position the wires and close up and re-tape the connector then re-tape the entire main cable back to the pcm connectors and re-install all connectors and assemblies in the dash that i took apart. needless to say the mic worked fine and no pcm or mic codes were displayed when i tried the various diagnostic code reporting methods. im thinking that this problem had nothing to do with the rain that happened the night before this problem started but i still dont know why the engine wouldnt start during the early phase of this situation. im glad i did this and not simply take it to the dealership and maybe those monkeys wiggle something and the problem goes away only to come back later. at least now i know where to look if it happens again. impressive tracking of the wiring through the harnesss what you didnt say if you are a mere mortal such as myself is the difficulty in following the factory diagrams in the manual. i know if i had not been in electronics field service and thus some exposure to how multi page diagrams are organized in general and that a manufacturer usually has their own adaptation of a wiring standard could have easily reached the frustration level where i just took it to the dealer. congratulations on a long and more difficult than you made it sound i would guess trek to find the offending component. i say that while also looking over my shoulder in panic thinking that if you have not uncovered a visible villain there is a good chance it will return. i hope not maybe it was a miniscule wire fragment that fell out when you unplugged a cable from a socket or something similar that made the bug disappear. even if you have it return judging by the level of detail in your post you will no doubt get it sooner than later again congrats.regards joe .