Engine/Transmission (1994 - 1998) Need Help?? no tach, no spedo, no alt, no cc, no od!!!

[TOshea]

Have no tach, speedometer, Cruise, overdrive, alternator. Checked all fuses and fusible links. Checked some senors. Found out no 5 v at sensors. Have 12 v in at pcm, but not 5 v out at pcm. Bad PCM??? Need opinions / Help???

 

[KWentling]

I would clean all the grounds you can find. The PCM ground is on the front of the engine at G105 by the book on my '98, but thats the only discription I could find for it. Looks like fuse 3 (20 amp) and fuse 6 (30 amp) in the PDC would be ones to double check. Doesn't sound good. You need to fill out you're sig. so we know what you're truck is. By the way, welcome to TDR.



Kim

 

[Howard Durand]

What year is your truck?

Your 5 volt circuit may be shorted to ground either in the cable or, more likely, at one of the sensors.

Try unplugging the wiring harness at the pcm then test the 5 volt circuit against ground with an ohm meter.

 

[TOshea]

Still need help / Updates!!!

Have constant 12 volts in at pcm. Been getting frustrated, I really need this truck for work. So I cut the 5 volt lines at the pcm to rule out any shorts. No 5 volts out, am I thinking correctly by this troubleshooting that it would be the pcm??

 

[Howard Durand]

I think you are right. It is most likely the PCM has failed.

An easy test would be to take a 6 volt lantern battery and connect it between the 5 volt wire and ground and try it. If it works with that lash-up, and nothing else is wrong, you could make up a simple regulated 5 volt supply fed from the 12 volt source and connect it in place of the battery.

I don't know if a solid ground on the 5 volt circuit would cause the PCM to fail or not but I would check it first before putting the battery on it.

 

[mwdean]

need help?? no tach or a/c

repl crank sensor

 

[TOshea]

Crank sensor

Don't think the 97 diesel has crank sensor. Thinking durand has a good idea about the 5 volt supply.

 

[Howard Durand]

It does have an engine speed sensor which privides information for several functions but if there is no reference voltage from the PCM it will not operate.

I think that a battery connected to the open wire of the 5 volt circuit would work. Six volts is excessive but not enough to damage anything and lantern batteries are easy to find.

I am concerned as to what caused the failure though so would be careful to make sure the 5 volt circuit is not shorted to ground. Possibly through a bad sensor.

If you don't have a meter to test for a short, put a small, 2 or 3 amp fuse in series with the positive lead from the battery when you connect it to the circuit. If it is shorted, the fuse will blow.

If the truck can be made to operate normally with this experiment, we can easily build a permanent regulated 5 volt circuit to by-pass the PCM.

 

[TOshea]

Update

Thanks durand, the truck is at a fellow who works for me. Will try battery and fuse hopefully tommorrow, if not first thing monday morning.

 

[Howard Durand]

Make absolutely sure it is the 5 volt wire you have cut. My manual is for a 94 and I know the wiring for the 97 is different so have no idea which pin on the PCM you check for 5 volts.

The 94 uses 5 volts for the TPS and 8 volts for the engine speed and vehicle speed sensors but I believe the later trucks use 5 volts for everything. The engine speed sensor is the one that controls most of the functions you have lost. The TPS controls the transmission.

 

[ndurbin]

There is a plug connection right infront of the #1 valve cover that if it comes loose well cause some of these problems. Check it and clean it with some electrical connection cleaner.



Nathan

 

[biggy238]

The TPS does control Lockup directly and not the shifts. . The TSS signals the shift points. I found that out this weekend.



Sounds like a PCM failure to me too.

 

[Howard Durand]

As noted above, the caution about grounding is important too. There is a pin on the PCM that is a ground return for the sensors. If the wire between it and the sensors is open somewhere you would have the same situation. You would probably not see 5 volts between the 5 volt pin and gound.

If you can identify which wire is ground for the sensors, try measuring between it and the 5 volt pin. If you still don't have 5 volts the PCM must be the problem.

 

[Vaughn MacKenzie]

I lost everything on my '96 a few months ago and the fix was a new PCM. Was unable to find a used one ANYWHERE in the USA so had to bite the bullet and buy a new one. Best price I found was www.mopar4less.com but you'll need a couple weeks' leeway with them.



Mine died because my alternator freaked out and went into full charge and killed the PCM from overvoltage.



Vaughn

 

[biggy238]

Mine died because my alternator freaked out and went into full charge and killed the PCM from overvoltage

I thought the PCM regulated the voltage?? PCM suicide... ...

 

[mwdean]

engine speed sensor is the crank sensor. it tells the pcm the engine is running & then the pcm turns on a/c, alt, & cruise control.

 

[Howard Durand]

It will be interesting to find out what the problem turns out to be. Several suggestions and several theories. Hope something comes of it.

 

[TOshea]

Got my truck back!!!!

After all the testing, everything came back to a bad pcm. Got a used one, and couldn't find anyone to program it. They said they could program a clean one, but couldn't remove vin info from previous vehicle. Took back used one and ordered a reman, the place I ordered it from preprogrammed my vin info, and everything is back. I appreciate all the help on this. Thanks guys!!!

 

[BigPapa]

Howard, I have a friend with a '95 auto that has done what TOshea's truck did. He said he started losing guages one at a time, then OD wouldn't work and now his batteries are dead. I could swap my PCM with his to trouble shoot it but I don't want something on his truck taking my PCM out. What would you suggest? I'm figuring:

1. Check grounds.
   
2. Check the plug Nathan referred to.
   
3. Swap PCM's.
   
4. Perform the 5V test you mentioned.
   

Is this what you would do?



Thanks,



Scott

 

[BigPapa]

TTT... .....



Scott