2nd Gen Non-Engine/Transmission No Speedometer, tach, A/C, or overdrive

[sgmans]

Just fired up my '94 3500 4x4 and noticed the speedo and tach weren't working. As I went down the road I noticed it wasn't shifting into 4th and that the A/C wasn't blowing cold. I'm thinking its got to be some kind of electrical issue, checked all the fuses and didn't find any blown. I did find evidence of a rodent under the hood.

Where do I start? I'm hoping someone else has been through this and can help me out.

 

[BigPapa]

Welcome to TDR.


There have been numerous threads on this. First, check fuse #1, should be a green 30amp, in the PCM. Also check fuse #9, should be a red 10amp, at the end of the dash.

If they're ok, it could be the Engine Speed Sensor that reads off the crank damper on the front of the engine. If there's no signal from it to the PCM, it doesn't know if the engine is running so it will not "turn on" the alternator or A/C and you won't get a tach reading. Make sure it is plugged up and the connectors are not corroded or soaked with oil. Check the gap, it should be @ .050". You shouldn't use a metal feeler gauge. Most standard credit cards are .030", so you could make sure one will fit and two will not. That should be close.

Lately, threads I've read end up being the PCM, though. Maybe we're finally nearing the life span of the early 12V PCM's after a bit over 20 years. If you know someone with a similar truck, '94 auto, you could use theirs to test. I would also check the PCM connectors for corrosion,

 

[GAmes]

First step is to get a factory service manual that contains all the wire diagrams, locations of connectors, grounds, and every thing else you need to chase wires. I prefer the paper version since I don't want my computer in the garage.
https://www.genosgarage.com/product/dfsm94-cd/dodgeram-factory-service-manuals
https://www.genosgarage.com/product/dfsm94-print/dodgeram-factory-service-manuals

Since the engine speed sensor does not provide info to the speedometer I think you can rule out the ESS itself, but both the ESS and the vehicle speed sensor (VSS) share a ground that might be the place to look first.

 

[BigPapa]

Since the engine speed sensor does not provide info to the speedometer I think you can rule out the ESS itself, but both the ESS and the vehicle speed sensor (VSS) share a ground that might be the place to look first.

I was thinking this same thing Gary, but wasn't sure.

 

[upf7flyr]

I just posted a similar problem, but my speedo doesn't fail. My cruise control doesn't work anymore but not sure it's related as it won't work while other problem is "un-failed". Just learned something else. Alternator not charging and air pre-heater is not
cycling when starting cold eng. like it usually does. I'll add this to my other post.
John G.

 

[BigPapa]

I just posted a similar problem, but my speedo doesn't fail. My cruise control doesn't work anymore but not sure it's related as it won't work while other problem is "un-failed". Just learned something else. Alternator not charging and air pre-heater is not
cycling when starting cold eng. like it usually does. I'll add this to my other post.
John G.

I read your other thread. I would give you the same advice as the OP here. Your PCM is on the passenger side firewall right behind the air cleaner.

 

[sgmans]

So I'm trying to find another PCM, mine had model # 5602-7303. The only ones I can find are the 5602-7304, does anyone know what the difference is between the two?

If I go buy a 7304, will it work in my truck?

 

[BigPapa]

As long as it's from a '94 or '95 auto it should be fine. I don't know about the numbers. I did find one on eBay from a 5-speed that was a 5602-7300.

 

[Mikey-KE7LBB]

I had the same thing happen to my '93. I had a broken belt and it took out the wires for the crank sensor.

I would look there first.

 

[dblake]

Check out this thread
https://www.turbodieselregister.com/threads/254003-Wow-never-seen-this-before?p=2471531#post2471531

 

[sgmans]

It ended being the Engine Speed Sensor that was bad. Replaced it and all is well.

I'm just wondering if I should replace other sensors too? Curious to know what the life span of some of these electrical components is? The truck is 23 years old.

 

[BigPapa]

I wonder why the ESS affected the speedo? That's a new one on me.

 

[Mikey-KE7LBB]

My guess is that the computer doesn't send the reference voltage to sensors until it sees the engine running.

 

[GAmes]

My guess is that the computer doesn't send the reference voltage to sensors until it sees the engine running.

You can disconnect the ESS and the speedometer will still work. Something else was at fault.

 

[GAmes]

It ended being the Engine Speed Sensor that was bad. Replaced it and all is well.

I'm just wondering if I should replace other sensors too? Curious to know what the life span of some of these electrical components is? The truck is 23 years old.

They are electronic items, subjected to weather, vibration and usually oil. No, there isn't a life span that can be calculated. Did you ever get a factory service manual or do you plan to just throw parts at it in the future?

 

[Missouri Mule]

In past threads I don't remember the ess causing the speed sensor going out. But tach, overdrive, definitely ess problem. When you add no ac the ess lost its ground and you need to run remote ground to it. I will need to look at the fsm to see if they have related wiring ess spds ( But there seems there was one more thing that acted up if the ess bit the dust..
If your engine dies but restarts (easy or hard?) its bent or loose pins in ess connector.

 

[sgmans]

Yes sir, I got a service manual from Geno's just as you suggested. I don't mind spending the money and replacing things before they go bad, or at least having them on hand for when they do go out. I was hoping that the folks on here would share their experiences, so that I could decide if going ahead and replacing some of these sensors would be in my best interest or not. This truck is not my daily driver but it is my "moonlighting" work rig, so when it's not running it ruins my day in a big way.

As far as the ESS fixing the speedometer too, I have a BD TowLoc installed on this truck. It taps into the VSS, I wonder if since the ESS was bad that maybe the TowLoc wasn't sending the VSS signal on to the PCM, and that's why the speedometer wasn't working as well. When everything wasn't working, I hooked my laptop into the TowLoc and the only sensor that was producing a signal through the TowLoc was the TPS. Maybe that explains why speedometer was out when it shouldn't have been, under normal circumstances.

Thanks again for all the help everyone!