I have a 1994 Caravan, 3.0l V6 3 speed automatic A/C NoCruse control.and for a while during humid/rain daysmy Speedometer would cut out, causing the van too go into Limp-home-mode and the check engine light would also go on. Turning the car on/off waiting a while and the problem would fix its self, until recently were it has cut out and not come back. the computer gave me code 12 and 15 12 is the battery disconnected message, and code 15 says the speed sensor. So I went too the junk yard, and tried 2 different speed sensors hoping too fix the problem, but no luck, and no speed sensor. At one point I had too replace the Body control module, and the temperature gage has never worked since I replaced it...I have tried opening every plug under the hood i could get myhands on, spraying them with contract cleaner and putting dielectric grease and reseting the connections, still with no luck.
Could a faulty BCM put up a code 15, and cause the problem / and or what else might be the cause of the problem?

 

Replace the speed sensor on the trans.

 

I Have replaced the speed sensor on the Trans, I tryed with 2 differint speed sensors.

 

Then the problem could be the cluster. unless you have a speedo cable.

 

How could I eliminate the Cluster as a problem ?

 

I also notice, not too sure if it is related, but the light were the gear selector is, has also stopped working...

 

Are you sure you only have a 3 speed trans, Because what you describing sounds like a bad ignition switch on the 4 speed trans. I also have seen the wires going into the output sensor break at the connector, and thats on the 4 speeds. There two ways to tell if have a 4 speed trans, 1) do you have a solenoid pack on the front of the trans and 2) do you have an overdrive button on the dash.

 

As far as i know, It is indeed a 3 speed, I don't think there is a solenoid on the front either, there are only too things I can see, one is the Speed sensor, Best way too describe it, like a Spark Plug with a 3 pin connector. And then there is a 2 wire connector going too something just above the hole too check the transmission Fluid. tried disconnecting it, and my computer gave me a Code 37, something about a tourqconverter release solenoid. I also thought the plug its self might be a problem... So I followed the wires back too the next connection, before it enters the PCM, and did a test with the multimeter, they all beeped Fine. Tested the plug with the ignition in the run position, one wire gives me 14v (13.95) the other gives me 8v (8.05) and the other gives me 0 Voltage. and the way I tested it was, One meter lead into the the plug connection, and one lead too the negative post on the battery