SPEED SENSOR PROBLEMS AGAIN, please help

[tclark]

I sure hope someone can help me with this problem, I am scratching my head over this one. The transmission speed sensor, I have replaced a number of these over the years that is for sure. I don't know why these things go bad but they sure seem to. I am the origianl owner of this truck and since new I have replaced at least 6 of these sensors. Well a couple of months ago it went bad again, which means no speedometer of overdrive, and I replaced it. 200 or so miles later it goes bad again, so I replaced it. Another 200 miles goes bad again, replace again. Guess what? Another 200 miles and goes out again! Well the dealership has so far been replacing these under warranty but that doesn't help me figure out why these are going bad. Anyone ever had this happen or have suggestions on where to start looking to fix this problem?? What I would REALLY like to know is how can I get my overdrive to work when this sensor is bad? Is there a way to bypass this thing? I can't pull more than 50 mph without the overdrive so my truck is basically out of commision when this sensor goes out. I sure would like to know how at least to get my overdrive working so I can drive it while I figure out what is up with this sensor. What should I do?

 

[KSommer]

on the ds of the transmission is the main plug that runs everything. look just above it and you will see 2 more wires, one i think is black, the other is i think orange with a black tracer (on my '91. 5) splice into the one with a tracer and run it up to the dash, to a switch and then to ground. flip the switch on to engage OD. this will not split any other gears, it only adds one more. I "shift" mine once i'm moving about 35-40 and remember to turn it back off when slowing down. if left on the truck will pretty much skip 3rd gear and go right into OD.

kent

 

[tclark]

Great, thanks I will try that, wish I could do it right now but it is raining at the moment. Thanks again, TC

 

[Philip]

Check the voltage going to your sensor. It should be around 5 volts. If it is higher it could be blowing the sensors.



Also check the contacts in the plug at the sensor. If they are loose it would give you the same problem. Plugging in a new sensor would make contact for a while. Then the problem returns. Is your harness secured close to the sensor or flapping in the breeze the way Dodge did it?



Look over the wiring going down to the sensor. I had mine rub threw last year. It caused a erratic speedo reading.

 

[tclark]

Thanks Philip for the ideas. Do you have any idea what could cause an increase in voltage to the sensor? I will check the contacts of the plug to sensor. A new length of wire comes with the new sensors W/ male and female ends but I never use it because the female end doesn't fit on to the plug going to the sensor. One thing about this problem is that it seems to be very regular... I mean it is lasting about 200 miles exactly and then the speedo flutters a little and then craps out. I am thinking you are right about the voltage for some reason being to high and causing the sensor to fail but have no idea of what to do about it. Hmmmmm... Thanks, TC

 

[Philip]

Are you using crimp terminals on the splices you are making? I never use crimp terminals in an app where weather can get to them. I use solder and heat scrink only.



Look real close inside the female end of that plug. You will see it has small tabs inside it. Bend these tabs back out with a small screw driver ( gently ). Then use some dielectric grease. I use GM brand it seams to hold better with age than Dodge or Ford brands do. I haven't found any other brands I like.



Check the voltage it should be 8 volts. Do you have a 2 wire or 3 wire Speed sensor?

 

[tclark]

Thanks for the help Philip. My Sensor is a 2 wire. Going to the sensor is a wire with a female end that accepts 2 small pins. There are no tabs on mine. It has a little rubber gasket thingy which is supposed to seal it and a plastic lock tab to keep the plug in place. With the new sensor comes an 8" two wire plug arrangement that has this same female plug on one end for the sensor and on the other end a plug with a male/female arrangment, 1 each kind of like a trailer plug but with only 2 plugs. When installing the new sensor I am not using the additional wire.

I will check the voltage ASAP. I suspect something is happening to cause the voltage to somehow burn the new sensor out. I will check the wire going to the sensor for rub through further up the line somewhere.

What I am wondering is if the voltage to sensor is not 8 volts, than what??

I am also wondering what kind of life other folks been getting out of these sensors? Isa this something that commonly goes bad or are my experiences out of the ordinary? Thanks again for the help. I had let my TDR membership lapse and had to sign up again to access this forum for this problem. There is literally no where else to go to get the kind of quality, straight, accurate advice as is available here. That I know for sure. TC

 

[DavidC]

If you have more than the required voltage an easy fix goes like this. Get a rheostat pot like 5kohms, cut the wire to the sensor and attach the positive wire to the pot+ terminal and the sensor wire to the wiper. Adjust the pot to desired voltage. Remove the pot without disturbing the setting. Put an ohmmeter across the pot where the wires were attached and that will let you know the resistor you need to solder into the wire.



Dave

 

[Philip]

Sorry I didn't get back sooner.





The speed sensor looks like it generates its own volt. On the diagram it show pin 7 as a 8 volt imput from the sensor. The second wire is shown going to pin 4 as a sensor return. But the sensor return is tied into just about every other sensor on the engine. They all junction together at K4. Don't ask me where K4 is located. LOL



Pin 7 on the PCM is in the top row 7th one from the right side of the plug. (looking it the connection that plugs into the PCM).



Pin 4 is the 4th one from the right side on the plug. Top row also.



Do a ohm test from the speed sensor plug to the two pins I listed and see if the wires show low restenance. If you showing high start looking for bad spots in the wiring or bad conection in a plug somewhere.

 

[ScottLewis]

I just changed out my speed sensor (TSS, 2 wire) which I suspect is like yours. I had nearly 98K miles on it, over 7 years old. I'm in Calif. though, so don't experience nearly the road salt and extremes of cold and snow you have.