i have tested the speed sensor on my 1998 mustangs reference wire and theres no voltage. I checked at the sensor connecter and at the pcm, so i beleive the pcm is at fault. I would like to send the pcm to get it fixed, but were are the best places that can be trusted to fix it. I live in Ottawa Il and do not know of any place around me that does this

 

Before you send the PCM out for repair, could you tell us how many wires go to your speed sensor. Two or three.
If its three, then you should have voltage going to the hall effect sensor as you stated. Were you able to verify that there is no voltage coming out of the PCM to the sensor by actually checking at the PCM ? Just asking in case there is a break or poor connection in that wire. Most of the time the input voltage to the sensor is 12 volts.

 

I checked at the speed sensor referance wire ( pnk/org ) and there is suppose to be .5 volts. It is a two wire and the other wire is ( gry/blk ) which the sensor sends information to the pcm which is a pulsing voltage of .5 volts. the wire at the pcm ( pnk/org) has no voltage at the run position or engine running. This is why i beleive its in the pcm. I was hoping that it was some where in the wiring but not so

 

If it is a two wire sensor it is a variable reluctance sensor which means you measure the AC voltage at the two wires as you pass the teeth in the output shaft past the sensor. You can do the same thing if you remove the sensor and pass a piece of steel back and forth across the magnet of the sensor. If you test it this way and get no kind of pulsating voltage from the sensor it is defective. Use the lowest voltage scale of your AC meter. If you do get the reading and you still have problems, now it's a good idea to confirm that there are no breaks in the wires

 

If the referance wire does not have any volts then how can the sensor produce a signal to send back to the pcm. I checked with a manual and it says first to check the referance wire and if there is no volts ( 5volts) the pcm is at fault. I crawled back under the car and checked it again and yes with the ac side and no reading with any scale seting. I feel that taking out the sensor to do a reading will be of no use if there is no volts going to it, if i am wrong please explain what i am saying. This car has only 18000 miles on it, and garage kept, mostly shows and cruise nights.

 

The sensors that have two wires have an internal magnet and as the field is varied it produces its own voltage signal that is measured as an Alternating voltage signal that increases in frequency as speed is increased.
A three wire hall effect sensor requires a reference voltage in order to work. Where is this sensor located that you are checking?
If the manual you are using is specifically for a 1998 Mustang (OEM) not just a general manual, than by all means go by the manual.

 

Its in the tail shaft of the trans ( manual 5 speed ) and the spedometer gear is on the end of the sensor. So you are saying that the two wires on the sensor has no volts unless it is spining

 

Yes, that is correct. You can check that sensor by connecting your meter to the two wires and have it set on the lowest AC voltage setting and spinning the sensor in your hand. You should a small voltage reading if the sensor is good.
If I may, why are you suspecting a problem with the sensor or PCM?

 

I was confused because the manual which was Haynes led me to run the first test which now does not make any sense. how can you test a wire when it is unpluged from the speed sensor, why they led you that way i do not know, but since the sensor produces its own ac voltage. If they would of said to back probe the connecter that would make more sense. So tomrrow i will take out the sensor, so thanks for your help and i will let you know the results

 

I don't know at this time I can help determine the cause of the problem, but it sure would help if I knew just what the problem was.