Chrysler Repair: Speedometer not working, chrysler lebaron, dc voltmeter

Question
QUESTION: I have a 1995 Chrysler Lebaron with an 3.0 automatic transmission. The speedometer is not working. It is showing code 15. I followed the test in the manual and it said the speed sensor was bad I replaced the sensor and it still does not work. I have checked the wires for continuity and they are all good. What type of signal should I get from the speed sensor on pin #13 and 14 on the TCM. Should I be reading Ac volts or DC volts. Could it be the TCM. The white and red wire going to the speedometer and the PCM has no signal on it but I am not sure of what type of signal it should have

ANSWER: Hi Paul,
The sensor produces a voltage pulse whose rate is proportional to the rate of rotation of the shaft of the sensor. To "see" it you have to have the speed of rotation rather slow (if using a digital DC voltmeter), but it can be more accurately assessed with an oscilloscope. You should be able to sense the pulses on a voltmeter by turning the gear by hand, I would believe, though I haven't tried this myself. I believe it is simply a coil turning within a magnetic field that is resonsible for the voltage pulses. Once the signal is received at the TCM it is converted to a digital signal (pulsing between 5 and 0.3V on the bus) so that it can be shared with other sensors' data on the digital data bus which can't be sensed by a simple voltmeter. I would believe that the problem is at the sensor (could it be mechanically inoperative?) or its wires to the TCM, or the speedometer cluster unit may be inoperative. If the transmission is shifting properly then I believe that the speed sensor is working. In that case I would check the wires from the TCM (pin 58) to the cluster and to the PCM (pin 47) which is white/orange. If you are getting pulses from the sensor, the wires are patent between all the units, then I would consider the possibility that the TCM is bad. But before investing in that I would consider a readour using the Chrysler DRB II diagnostic reader.
Roland
PS Please let me know what you learn. You can use the "thank/rate" to get back to me without having to wait for me to be available for a question.

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QUESTION: Roland,
I checked all the wires and they all have continuity. I even did the checks the manual says to do on the speedometer. The transmission does not shift but I thought that was because the sensor was not working. I will have to check to see if the ring in the transmission is spinning maybe it is an internal transmission problem. You said there was a digital signal from 5 to .3 volts.  What type of equipment can I use to check that.

Answer
Hi Paul,
I think you would need some sort of a digital data bus meter, and probably a rather sophisticated one, not just a code reader. I would say if you can verify that you can detect the slow pulsing of the sensor itself when it is turned slowly by hand, and also verify that it pusles when the you have the front wheels off the ground and the engine idling and the trans in 1st gear (low effective road speed), then if the wires are continuous to the TCM, and from the TCM to the PCM and cluster, and you still get no speedo and you get code 15, that I would turn to the TCM as the problem. The data bus pulsing is not something you can measure with a voltmeter. You would want to disconnect the battery from time to time as you do these testings so as to erase the fault code 15 each time you try to assess for the code situation.
Roland