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Discussion Starter #1
Hi all, i have a non working speedo and i tested the tranny vss and it is supposedly good(at least good enough to get a flicker out of the speedo) i do not have any movement out of my speedo even when key is first turned on. i also have tested the rear sensor on the diff and according to the autozone diagnostic charts here http://www.autozone.com/az/cds/en_us/0900823d/80/0f/f9/18/0900823d800ff918/repairInfoPages.htm
it says to ohm's test the rear sensor and if its over 2500 ohm's replace it, there is another one that says if it is under 1000 ohm's replace it as well, mine falls in right in the middle at 1800 or so.

i dont know where to start on this problem, i am just testing everything i can considering dodge fsm's throw parts at stuff long before actually figuring out what things are:):lol3:
 

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The sensor on the rear axle you can forget about. It is part of the ABS system Dodge put on the truck. You realy do not want that system to work. Beleave me on this one.

Hook the VSS up to a drill and spin it. See if the speedo give a reading then..

The drive gear in the trans is a plastic gear. I have seen the strip out. If you go to pull it and check it. Clean off all the garbage around it. Look real close at the mounting. There are numbers on the adapter assy. Be sure to reinstall the number that is located at the 6:00 position back to the same point. If you do not it can blow the gear if it is a good one.

If the gear checks good. Then the only other option is to ohm out the leads going to the speedo. If they check good. Its time for a new speedo head.
 

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Discussion Starter #3
philip thanks for all your posts. I did a drill on the speedo and it does not work. i ohm tested the vss and it shows it works(i.e. ohms on ohms off etc.)
 

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Discussion Starter #4
so for sure the speedometer is completely independant of the rear wheel sensor?
 

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The ABS system is stand alone. The controller for it is mounted behind the glove box.

If you go to pull the speedo you do not need to remove the gage cluster. Just pull the plastic cover off the cluster and the speedo pulls straight out of the cluster. It is held in by tension on three studs on the back side of the speedo.

There are some differences between your 91.5 and the 92/93 year models. My 93 FSM wouldn't be of much help.

Do you have power to the VSS plug???
 

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Discussion Starter #6
i checked before i started messing with the rwal stuff, and i had 3v or so to the vss, i think it was supposed to have 5v but do not know for sure as i cant find an fsm or anything that says. i figured if its got 3v and supposed to have 5v it should be enough to get at least a little bump out of the speedo
 

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5 Volt is what my FSM shows. 3 volts should be enough. My 5 volt circuit is only putting out around 4.0 to 4.5 volts. I had my tach output circuit on a O scope a couple of years ago.

About the only thing left to test is the wire going up to the speedo. Remove the speedo head and ohm the wire to the VSS. If it shows as good then your speedo is dead.
 

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Discussion Starter #8
i will check that, you think i should ohm from the speedo head where the round plug plugs into the back of the cluster and then run a wire down under the body to the vss? otherwise i dont know how to ohm the vss wire
 

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Remove the speedo head assy. Then test from the speedo terminals to the VSS. You could use a piece of wire if you meter leads aren't long enough.

While the speedo head is out the center terminal for the speedo should have 12 volts on it. With the key in the on position. The third terminal is a ground. Check it also.

Before going that far check the dash grounds. They are located behind the OD button on the right side of the column in the lower panel. Drop the panel off from under the column. then take a flash light and look at the support brace behind the OD button. you can see the screw with the ground wires.
 

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Discussion Starter #10
well, removed the speedo head, tested for voltage, got negative on the bottom one, 12v on the middle one, and 3.5v on the top one. then turned the key off and continuity checked the vss and it was just like it should be. argh still no speedo.
 

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Well your to the point now you need to try another speedo head assembly.
 

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What ever happend to the good ol days when they had a cable?? Sounds like a pain.
 

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Off topic, but need help

Philip,
Is there any way you can post the wiring diagram for the cruise control for me. I posted the request in the non powertrain and didn't get a response. I'm pretty sure it'll be the same as my 91.5. Thanks
Steve g
 

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Steve I don't have a scanner. Plus Dodge also has a supplement book out for cruise control troubleshooting.

There are actualy three manuals for our truck. The big one is the FSM. But it is lacking in some places. The other two manuals are 5.9L cummins diesel truck power train diagnostic and charging/speed control powertrain diagnostic procedures.

The 5.9 power train book covers wiring that is diesel only.

The 4th manual is for recall TSB's.

I have all 4 manuals but I don't have anyway for scanning to post info. I might soon. My main computer died a few weeks back. I should have it back up and running this week. During that time I came into posession of a newer scanner that will work with Windows XP.
 

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Discussion Starter #15 (Edited)
Phillip, to your knowledge or in the books does it say if cruise control would work with a non functioning speedo(from what i know it will not) any idea what dies in them?

also you said there may be a difference between 91.5 and 92 speedo heads?


Richie, your absolutely right it is a P.I.T.A this whole thing makes me remember why i shy away from most dodge/chrysler built vehicles :p
 

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Phillip, to your knowledge or in the books does it say if cruise control would work with a non functioning speedo(from what i know it will not) any idea what dies in them?

also you said there may be a difference between 91.5 and 92 speedo heads?


Richie, your absolutely right it is a P.I.T.A this whole thing makes me remember why i shy away from most dodge/chrysler built vehicles :p
I'm pretty sure that it will depend on why your speedo isn't working. It definately needs a signal from the VSS (vehicle speed sensor), but it may take it's signal off the speedo head rather than directly from the VSS. This is where a wiring diagram is nice.

I don't think you will find any manufacturer using speedo cables since the 90's. They may be more difficult to diagnose without a wiring diagram (a breeze if you have one), but I can tell you from 30 something years of experience that cables weren't without their problems. Dry, kinked, or too heavily greased cables causing the needle to bounce off the pin when they're cold, sometimes breaking the needle off. Replacing the cable on a car that was built with a speedo cable cable going down an assembly line then they wrapped a car around it. Removing the instrument cluster on anything is easy now that you don't have to f*** around with reaching behind it to squeeze a hard plastic retainer that only goes on with ease, then trying to get it indexed into it's square drive and plug the stupid thing back in with your arm contorted and twisted into a space the size of a flea's ear. No, they don't build them like they used to, thank God.

Thanks for your efforts Philip. If you do manage to scan it, give me a PM or post. I suspect the problem's in the clock spring, but it's pretty hit and miss without being able to do a logical trace.

Steve g
 

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On our trucks the PCM has to have a VSS signal. The cruise is controlled threw the PCM.

There is a splice in the VSS signal wire that provides the signal to the PCM. I haven't went threw the manual hard enough to find where it is located. If you have ever used a Dodge manual before it will give you a headache trying to find splice locations. :(

I don't think there are any differences between the 3 year models on the speedo head. There are some differences in wiring. The 91.5's and early 92 do not have a tach provision for one. I have heard the PCM is 91.5 only or at least the programing might be.
 

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Discussion Starter #18
can you look in your book and see if it shows the wires on the vss. i only have a 2-wire vss and only 2 wires going to it...i dont see how it gets a signal off the vss
 

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You two wire VSS has one wire with power to it. The other wire is the signal wire. The other splice is in the harness somewhere in the engine bay. I have found the location yet. I went threw about 10 different pages it sent me to and still didn't find the location of that splice. I'll look later on this evening and tell you the PCM pin number the VSS signal is so you can check there.

Maldon if your cruise is working then the PCM is getting a signal.
 

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Discussion Starter #20
no cruise or o/d or speedo if i can test the pcm pin out for the vss signal that should help some
 
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