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bill
bill, dodge master tech
Category: Dodge
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Experience:  25 years with dodge drivability and electrical expert
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98 dodge ram 2500 no communication with scan tool no gauges,

Customer Question

98 dodge ram 2500 no communication with scan tool no gauges, odometer flashes,
Submitted: 1 year ago.
Category: Dodge
Expert:  bill replied 1 year ago.

does the truck run?

can you communicate with the other modules on the truck (air bag and abs)

the bus originates at the cluster so depending on how you answer there can be several different conditions present

Expert:  bill replied 1 year ago.

at the DLC what are the bus voltages?

Customer: replied 1 year ago.
the truck runs and drives no elec od obviously. I cannot communicate with other modules I also tried using global obd2 no luck. bus voltages were2.49 2.51
Expert:  bill replied 1 year ago.

OK the bus originates at the cluster so with no communication and a "NO BUS" flashing in the odometer the cluster is where the failure is MOST likely, IF the truck didn't run then I would head to the engine computer (pcm) cluster failure was pretty common on that body style and a used cluster is OK IF can get one from a running salvage truck so you can see there is no failures in the replacement.

another choice is have yours repaired by a electronics shop that knows their way around these computers, YES the cluster IS a computer actually the body computer for this truck, also BE SURE to swap over the remote keyless entry module on the BACK of the cluster or (if you have it) the remote keyless entry will not work

Customer: replied 1 year ago.
ok the odometer isn't flashing no bus just flashing mileage which isn't increasing lol. completed cluster self check and retrieved codes 920 921 999 which I found descriptions for. doesn't really make sense seeing as I have bus voltage at dlc.
Customer: replied 1 year ago.
when doing Chryslers 4a or 5a procedure for the condition my resistance on the bus didn't come into spec when cluster was removed
Expert:  bill replied 1 year ago.

ok what is the entire story here what is your skill level and what procedures have you performed, IF you cannot communicate with any module that's almost always the cluster, in my 28 years with dodge I have seen runs on clusters on the older trucks, did you do the tests with all the modules unplugged? since all the modules will have a termination resistance, if you have the correct voltages that indicates no shorts or open circuits, the 2 legs of the bus must equal 5 volts, you MAY have an issue with the terminals on the DLC or your scan tool, are there any warning lights on in the cluster?

and here's a great test hook up your DVOM to the DLC bus terminals and with the doors all closed wait till the bus goes to sleep, the voltages will steady out, then hit the remote keyless entry or turn on the key and see what the voltages do they should start jumping around as the different modules start communicating, IF they do then there is nothing wrong with the bus, look for spread terminals in the DLC or look at your scan tool

Customer: replied 1 year ago.
ok im a journeyman tech no dealer exp . I have account with identifix which gives me access to Chrysler service information but most tests are with drb 3 which I do not have. I have done most of the tests for short to ground ,power,open that the service info has given me I found one more just a few minutes ago that im goin to try out. I unplugged modules one by one while monitoring resistance which I what I understood from the procedure definetly could have mis read.. I wast to familiar with termination resistance . warning light for abs, seatbelt,fuel are on at all times. i tried 2 scan tools and its been to the dealer who told me pcm and i am always very sceptical of jumping to that .
Expert:  bill replied 1 year ago.

don't be skeptical pcm failure can easily kill the bus and cause issues.

I would like you to perform the test I listed last to see what the bus is actually doing

and also look VERY carefully at the pins on the DLC its EASY to get a spread one especially on this 16 year old truck.

when ever you do a short to ground or voltage test you need ALL the modules unplugged.

your identifix subscription should allow you to see how the bus works and give a good explanation of its operation, which is needed on this system, you need to understand it first so you can interpret the results.

I taught for a short time before returning to dealer life and that was the hardest thing, getting my students to understand, they needed to understand how a system worked before they could diagnose it, I still have techs under me that don't het that too loll

Customer: replied 1 year ago.
i went over the module layout a couple of times its pretty straight forward. i will head out there this evening again .the idea of cluster is settling in i swapped the pcm earlier in the endeavour from same year truck with no result. just wanted to clarify if i measure voltage between bus + and bus- should i get 5v or no
Expert:  bill replied 1 year ago.

no test each leg and it should be around 2.50 volts and will vary when the bus is active from around 2.45 to 2.58 the number between the 2 legs should add up to 5 volts.

also unplug EACH module on the bus and see what happens if you unplug a module and suddenly the truck comes alive and you can communicate that module is defective and killing the bus, these modules are daisy chained in series-parallel so if one goes down they all go down and when you pull the dead module the bus comes alive

IF you have a steady number and NO variance the bus is static and nothing is communicating, wiring is NOT too common on the older systems however modules were

Expert:  bill replied 1 year ago.

I am logging off for the night 5:30 am comes early on the east coast I can check my email throughout the day tomorrow and respond when I can

Customer: replied 1 year ago.
howdy sorry for being gone was on a service call. i rechecked my connection at the dlc and they didn't look hogged out. i check the bus voltage again and it was ranging from 2.450-2.468 i tapped the brake and such while i was monitoring and it stayed in that range. i hooked up the scan tool again and was able to communicate with the abs module but that's it. i tried unplugging each module again with no change with the cluster. im starting to wonder if i have made a mistake when checking wiring maybe bad ground to cluster.
Customer: replied 1 year ago.
oh and i wanted to add that before this problem occurred with the cluster i had a problem with my tps being pegged a 4.68v causing problems with od and tcc
Expert:  bill replied 1 year ago.

I assume this is an aftermarket tps, have you tried unplugging the new tps and seeing what happens?

those bus numbers are not indicating a fault in the bus if there was a short there would be 1 leg at 0 or much lower than the other

what codes were setting in the abs module?

Customer: replied 1 year ago.
im not sure whether it oe or not i swapped it with one from another truck that was fine also tried with it just unplugged. i also unplugged ess,vss,o/p,fuel,heater, coolant temp,cruise control. i also found an article in identifix regarding the relation of the clockspring and the 5v ref for tps , unplugging clockspring had no affect. no codes in abs module but warning light is on.
Expert:  bill replied 1 year ago.

there has to be a code in the abs if the warning is on UNLESS the cluster had died and is triggering all the lights, lets go to the beginning of all the problems, when did the problems FIRST start

Customer: replied 1 year ago.
truck had cycling issues from first day i owned it. found broken throttle valve cable replaced and adjusted . was better but still wouldn't unlock the torque convertor on its own always had to tap the brake and floor it . checked for codes none checked data, tps voltage was a little low and it only went to 82 % . measured distance between throttle cable bracket and lever and it was way out of adjustment. i adjusted length ,noticed throttle cable was really tight so i replaced it as well. went for test drive and it wouldn't go into overdrive until i hit exactly 90km them it would go into od then lock tc immediately after. so i re adjusted TV cable and test drove again then no OD or LU . this time hooked up scan tool and tps was at 4.68v. that's when i started to remove connectors while monitoring my scan tool each time for my voltage to drop which it never did. so i started pulling the loom apart at the ess to the firewall and the junction where it heads doen to the transmission all looks well. then i hit up identifix and read a post about cutting the 5v ref at the pcm to eliminate shorts in main engine harness .i turn key back on and checked my scan tool dun dun dun no communication and no gauges. reinstalled everything repaired wire and still nothing. checked all fuses then started with the module unplugging .
Customer: replied 1 year ago.
in between then and contacting you i have check my powers and grounds at pcm , replaced pcm with used no dice took to dealer and dealer told me pcm yes i get i could have 2bad ones for sure but i get no voltage on 5v ref with original pcm and .450 with replacement kinda made me think something else was causing it to shut down. probably the cluster haha im gonna source one in the morning
Expert:  bill replied 1 year ago.

ok with the wire you cut, cut again what is the voltage on this wire and what terminal the pcm is it

I would also like the vin to pull a wiring diagram and compare the wire to the one you think it is, it is POSSIBLE this is NOT the 5 volt reference wire and another one, if the 5 volt reference was shorted to ground the truck would be dead, and would not run at all

Customer: replied 1 year ago.
pin 17 violet and white black connector pcm when i had everything undone i check resistance from the tps to pcm connector on that pin. is there a way for me to give u my vin without posting it .... just curious being its the 12v wouldn't it still run i thought the fuel solenoid ran of ignition
Customer: replied 1 year ago.
ok i just went and cut the violet/white pin 17 balck connector and i have 5.12 which blew my mind because i did this exact same thing the other day and got nothing .
Expert:  bill replied 1 year ago.

no one can see your vin except me and IF someone somehow can see it that IS NOT and expert it is meaningless to them I need the vin to be 100% sure we are on the same page, all the info on my tech page with Chrysler is vin specific

Expert:  bill replied 1 year ago.

ok with that wire cut what is happening to the gauges? and can you communicate now with the other modules?

Expert:  bill replied 1 year ago.

sounds like you disturbed something in the wiring harness and caused a short to ground on the 5 volt reference wire you cut

Customer: replied 1 year ago.
1B7KF23D9WJ124160 no changes to cluster ill run out and try scan tool again. that was my first assumption i have had the entire engine harness out of the loom i repaired a stripped nut on the c130 connector at the pdc that was stripped and not tightening down all the way.i repaired 2 wired that someone had put scotch locks on to accomidate a switch for lock up
Customer: replied 1 year ago.
ok so still no communication with scan tool except abs. i was looking under 4wal instead of the rwal and got a bunch of codes mostly from me unplugging things it seems. in order from top to bottom 78 foundation brake/35 rear sensor open/37 intermitant signal rear speed sensor/ 84 mismatched vin/65internal main relay open/52 rear dump solenoid. cleared codes non came back
Expert:  bill replied 1 year ago.

did you know there is ANOTHER 5 volt supply on the WHITE connector of the pcm it is orange on pin 31 is there a orange wire in that connector? the wiring for the diesel was interesting to say the least

the 5 volt on pin 17 feeds the engine speed sensor and cam position sensor (IF equipped) on the diesel

Customer: replied 1 year ago.
i did know only because i was investigating the bus wires in that connector i didn't know what to make of it
Customer: replied 1 year ago.
i have been having a lot of trouble with diagrams it is also a split year so it made it extra special lol
Expert:  bill replied 1 year ago.

that's why I needed the vin, my diagram comes up as a BE body QUAD cab with a heavy duty cummins turbo diesel.

this thing should have an ECM AND a PCM

Customer: replied 1 year ago.
there is an orange wire but not sure what tracer i do know there is more than one orange wire in that connector one for sure has a black tracer
it defintaly does NOT have an ecm i thought that was for the 24v engine
Expert:  bill replied 1 year ago.

which may be some of the issues with communication you are having some generic scan tools will NOT communicate with the cummins ecm (on the side of the block)

Expert:  bill replied 1 year ago.

ok so this is a old 12 valve then

Customer: replied 1 year ago.
Expert:  bill replied 1 year ago.

the wire should have NO tracer just orange

Customer: replied 1 year ago.
yup there is
Expert:  bill replied 1 year ago.

my diagram shows an ecm but I know this was a mechanical injection system so that makes it more interesting

Expert:  bill replied 1 year ago.

does that wire have 5 volts on it?

Customer: replied 1 year ago.
it does
Expert:  bill replied 1 year ago.

also have you gone back to 1997 to compare the diagrams to your truck since this is an early 12 valve it MAY have been wired as a 1997

Customer: replied 1 year ago.
a lot of what im going off of is a Chrysler paper service manuel that i got from a friend i went to SIAST with i cant remeber if it is up to 96 or 97 on Mitchel i have only checked 98
Expert:  bill replied 1 year ago.

all this started after you cut the pin 17 5 volt reference

Expert:  bill replied 1 year ago.

your identafix should be able to bring up 1997 as far as I can go is 1997 for now until the idiots in Detroit get their asses in gear and put the rest of the info online

Customer: replied 1 year ago.
black/blue ground was cut just prior to cutting the 5v but i reconnected the ground before trying the 5v
Expert:  bill replied 1 year ago.

in 1997 the orange wire is the 5 volt for the speed sensor on the tranny and for the governor pressure sensor inside the tranny

Customer: replied 1 year ago.
signal wire at tps is org/lightblue
Expert:  bill replied 1 year ago.

ok the only thing I can think of is a poor connection at 1 of the 2 wires you cut OR poor pin fit at the pcm,

what methods did you use to reconnect the wires and you are 100% sure you didn't mix these wires up right?.

to check for poor pin fit you will nee something like a small sewing needle that fits snug in a known good pin then check the other pins in the pcm connector if it feels looser those pins are spread and will cause a poor connection, remember there is NO amperage on these wires so connections MUST be near perfect

Expert:  bill replied 1 year ago.

that's right that wire should go directly back to the pcm

Expert:  bill replied 1 year ago.

it must have no resistance on that wire

Customer: replied 1 year ago.
that wire has 0 resistance and it does go straight to pcm .ok i soldered and heat shrank both ill recheck them and look at the pins what can i do as a correction for the pins i have already put a sliver of dielecric grease
Expert:  bill replied 1 year ago.

IF there is a loose pin there should be a connector repair kit available still and you can swap out any loose pins

Expert:  bill replied 1 year ago.

we have always and still do have (as do all manufacturers lately) pin fit issues I had a dart drive a tech up the wall wit a fault code that ended up being a sloppy pin in a body harness of all places but it was a sensor wire and with no power except a few volts running through it the sloppy pin caused major headaches

Customer: replied 1 year ago.
ok so i used one of the pin probes that was in my backprobe kit it had slight drag on a few holes of the gray connector then checked all . they all had a little drag in and out none of the physical pins on the pcm look problematic looking into the connector they look fine
Expert:  bill replied 1 year ago.

wit the connections made and all the sensors hooked up what is the pcm putting out at one of the sensors on that 5 volt reference?

do you have the ORIGINAL pcm to swap back in? my thought process is it has to be something either in the wiring or the pcm that is killing the communication, these harnesses were brittle when new and I am thinking MAYBE there is a hair of a wire out and causing the comm loss.

if you go back to1997 compare the pcm pin out to that on your truck there were some differences I saw and 3-5 volt reference wires, if you can take the truck on a short drive and see if anything is not operating correctly since this is a 12 valve it will run with the pcm down BUT there MAY be some shift concerns speed control speedometer etc

Customer: replied 1 year ago.
Ok I will go check the original pcm is what is in it now. My cruise has never worked I drove last night drives and shifts fine other than no overdrive. The mismatched vin code came back in abs even though the original pcm is in . Park brake light,abs,seat belt and fuel light are on
Customer: replied 1 year ago.
I have been driving the truck daily . All gauages remain inoperable
Expert:  bill replied 1 year ago.

the mismatched vin is interesting too and is most likely the cause of the abs and red brake light being on, was the dealer able to communicate with any modules with their DRB 3 by chance??

I would love to know what vin is in the pcm that is in your truck and the vin of the pcm you installed as a test.

in the lower 48 we have to put the vin on the receipt not sire about Canada

have you checked t the cluster connector for bus voltage power and ground?

I'm gonna say the cluster is powered since there are warning lights but have you checked the bus voltages

Expert:  bill replied 1 year ago.

if by chance the salvage yard gave you a gas pcm it could have caused some problems

Expert:  bill replied 1 year ago.

with the original pcm back in I would do a battery disconnect for 10 min the ABS module SHOULD relearn the original vin and clear the mismatch code

Customer: replied 1 year ago.
Dealer was a f..in joke they didn't even try to check other modules just plugged it in kicked it out and billed me 150 . I pulled the pcm myself out of a diesel pcm had same part number. I checked power and ground at black connector of ipc
Expert:  bill replied 1 year ago.

ok lets start with the original pcm back in and check the bus voltages at the cluster they will be a twisted pair the same color as on the DLC I would check them cluster unplugged and plugged in

Customer: replied 1 year ago.
I have only been checking bus voltages at dlc should I b trying to back probe at cluster I thought cluster controlled bus voltage ? If it's good at dlc wouldn't it b good at the cluster
Customer: replied 1 year ago.
Ok so original pcm installed I have 5v at tps. Bus voltage at cluster is 2.48 voltage drops to 0 when unplugged
Expert:  bill replied 1 year ago.

with the cluster undone what is the voltage at the dlc and pcm

sorry this is taking so long but loss of communication is a major PIA and more difficult when I can't actually see the truck

Customer: replied 1 year ago.
No problem on the time just glad I'm moving a little bit forward and the education is worth the money lol and your referring to bus voltage right
Expert:  bill replied 1 year ago.

yes the bus voltages

Customer: replied 1 year ago.
Ok so voltage at dlc is 2.424 cluster installed and nothing removed . Just wanted to clarify I'm only getting voltage on the bus key on
Expert:  bill replied 1 year ago.

yes key on check both legs as one leg down will kill the bus these older bus systems were very reliable BUT not fault tolerant, and what is it with the cluster unplugged? I am trying to see if the cluster is doing anything to the bus, also d the check with the pcm unplugged, the bus wires are the same color everywhere on the bus and always a twisted pair, so you just need to unplug the connector with the bus wires in it

Customer: replied 1 year ago.
ok so
wht/blk 2.457v at DLC cluster installed
-vlt/br 2.452v at DLC cluster installed-wht/blk vary from 189mv-350mv at DLC cluster removed
-vlt/br vary from 189mv-350mv at DLC cluster removed-wht/blk 2.458 at PCM connector cluster installed
-vlt/br 2.451 at PCM connector cluster installedresults at pcm connector same at dlc with cluster removedwht/blk 2.445 at DLC with PCM disconnected
vlt/br 2.466 at DLC with PCM disconnected
Expert:  bill replied 1 year ago.

I'm gonna have to say it looks as if the cluster has given up, your probably going to grab a salvage one so IF you can see if the one you grab works, my tech connect Is acting stupid this weekend but you should have a centeral timer module as well which is nothing more than a body computer do the wipers, lights and remote keyless entry work?

trying to see if these modules are down or just a fubar cluster

Customer: replied 1 year ago.
Lights and wipers all work door locks haven't worked since I got it radio works everything in the overhead console works I don't have a key fob
Expert:  bill replied 1 year ago.

ok I am still leaning toward a cluster you have proven the cluster originates the bus by disconnecting it and losing all bus voltage, and the bus is operational at least to the "bcm" which controls the wipers etc.. all the info that is out is bussed to the cluster or hardwired and the entire cluster is dead so that leaves little else than the cluster.

Customer: replied 1 year ago.
Alright cluster finally got here I had to order it in so I didn't get to physical see it work that being said I installed and still no gauges . Odometer still flashes and when I ran the self test on the new cluster it came back with the same three codes 920,921,999 . I reinstalled my original cluster . I started checking pcm output again and I'm not getting my 5 v ref anymore on both the vio/why and the org wtf is with that.
Expert:  bill replied 1 year ago.

sorry about the delay I have been in school and just got in, but still have to go back this week

loss of the 5 volt reference is either an internal fault in the pcm or a sensor shorted or JUST a hair of a wire exposed and touching ground somewhere, with the no amperage voltage only circuit of a reference wire even a hair of a wire touching can kill the reference, I would go back and recheck all the pins and any of the harness you opened I bet there is a bad pin in the pcm or a chafed wire, I would even go as far as pull open the harness and find the splices and redo them if they are even questionable, I still would replace the pin on the pcm connector.

what happens when you swap in the used pcm?

it will set vin mismatch codes yes but we are just looking at the 5 volt reference

Customer: replied 1 year ago.
Ok I'll have to get the pcm back to try it again. I unplugged the connector and cut both 5v ref wires at the pcm connector would that have eliminated a chafed wire in harness?. I will pull connector apart and grab a pin kit tomorrow
Customer: replied 1 year ago.
Ok so I replaced both pins for the 5v ref wires org and vio/wht with no result . There has to be a better way for me to narrow it down rather than just redoing every splice and like I said no n the previous post would me cutting the wires at pcm not eliminate a chaffed wire/ other short .