Testing a bad Speed Sensor (VSS)

[GreasyBob]

Hello everyone I'm new here, but I hope you don't mind giving me some advice. My 1994 taurus (automatic) has been having problems shifting gears. A local mechanic suggested that I check the VSS before giving up on the transmission. Would it be ok if I just unplug the speed sensor, and then drive the car to see if it shifts smoothly?

TYIA

[Dave_s]

You can pick up a new speed sensor for about $20. I would advise putting in a new one to see if it fixes the problem. Are you sure its the speed sensor? Does your cruise controll work? does you speedomentor swing back and forth?

[GreasyBob]

Originally Posted by Dave_s

You can pick up a new speed sensor for about $20. I would advise putting in a new one to see if it fixes the problem. Are you sure its the speed sensor? Does your cruise controll work? does you speedomentor swing back and forth?

Ok here is the full description of my problem. Everything works fine for the first mile. When the temperature hand rises up to about normal the transmission seems to start falling out of gear, and does not shift correctly. It also makes a whining sound except when I put it in park. The speedometer seems to be working, and cruise control has the same problems.

[shorod]

When's the last time the fluid and filter were changed in the transmission? What is the condition of the tranny fluid currently?

If it smells burnt, you may want to start by having the fluid and filter changed to see if that helps out. If during the service a bunch of large metal pieces are found on the magnet in the pan or in the filter, then it's time to think about rebuild or finding a replacement car.

I guess what I'm getting at is if the fluid and filter have not been changed recently, it won't be a waste of your $50 either way. You may either find that the tranny is about to leave you stranded, or you may have a bit more confidence that the issue is in fact not transmission but rather something electrical, etc.

I've realized that very few people are as diligent about servicing the high dollar transmission as they are about changing the engine oil and filter.

-Rod

[GreasyBob]

Originally Posted by shorod

When's the last time the fluid and filter were changed in the transmission? What is the condition of the tranny fluid currently?

If it smells burnt, you may want to start by having the fluid and filter changed to see if that helps out. If during the service a bunch of large metal pieces are found on the magnet in the pan or in the filter, then it's time to think about rebuild or finding a replacement car.

I guess what I'm getting at is if the fluid and filter have not been changed recently, it won't be a waste of your $50 either way. You may either find that the tranny is about to leave you stranded, or you may have a bit more confidence that the issue is in fact not transmission but rather something electrical, etc.

I've realized that very few people are as diligent about servicing the high dollar transmission as they are about changing the engine oil and filter.

-Rod

Tried that as soon as the problem started. The fluid looked normal and there were no metal pieces.

[shorod]

You can use a multimeter and battery drill to test the speed sensor out of the car. Set the meter to "ohms" or "resistance" and meaure the resistance across the windings. You should have somewhere between 190 and 250 ohms.

You can also set you meter to VAC and connect the leads to the speed sensor. Now use the battery drill to rotate the VSS. You should get an AC signal. The signal amplitude will likely change as the speed of the sensor speeds up and slows down. If you were monitoring the signal output from the VSS on an oscilloscope, you'd see the frequency of the sinewave change relative to the speed of the sensor.

You may also want to search this forum for "TRS" or Transmission Range Sensor. This part has been a common item to fail and it seems to cause all sorts of issues, some transmission related and others seemingly unrelated.

-Rod

[GreasyBob]

Originally Posted by shorod

You may also want to search this forum for "TRS" or Transmission Range Sensor. This part has been a common item to fail and it seems to cause all sorts of issues, some transmission related and others seemingly unrelated.

-Rod

That TRS sounds like it could be the culprit as well. It is also located where the local mechanic told me to look for the VSS.

[Bassasasin]

BOY DO I WANT TO TELL THIS...
Mine (transmission) did the same thing.. but it turned out to be the VSS ground line on the upper fender well drive side, inside engine compartment under a green metric screw bolt loose. that goes straight to the VSS sensor. .. I did replace the sensor.. kindof tough. Blind reach and all. But it didnt seem to help. Go and tighten all the electric wires you can reach. Even the red one at the firewall box on that side.

MY POST
I have a Taurus that had a BAD violently jerking transmission..
My trannie ran sometimes ok. for maybe 5 or more miles. (intermittent)
After AAMCO told me a new Trannie was needed.
I figured intermittent was the key to it NOT being the trannie.

I found that the VSS is controlling the computer to shift tranny and cruise control.

The solution was proubbly a bad VSS.OR

Bad battery connections.
My terminals were corroded.
Bad battery to RELAY box (firewall driverside red cable).
My nut was loose to relay box.
Dirty or connection to VSS on VSS sensor. 2 pins dark green /orange yellow.
My connection pins were black and not shiney. Hard to reach just under exhaust manafold.
Dirty VCC ground.
My VCC connection ground (green screw with 2 orange/yellow 1 black wire) on wheel well justback from beside the battery.. Cleaned but looked ok.

Worst connection was at the relay box large red connection nut was movable by hand but almost snug, but I cleaned them all first and the problem has gone away. For now. (50miles) never made it 5 before.

NOW (9/2006) NO PROBLEMS 1000Miles


GOOD LUCK

IT WAS WAY TO EASY TO FIX.. .hope its the same as yours.

[GreasyBob]

Originally Posted by Bassasasin

BOY DO I WANT TO TELL THIS...
Mine (transmission) did the same thing.. but it turned out to be the VSS ground line on the upper fender well drive side, inside engine compartment under a green metric screw bolt loose. that goes straight to the VSS sensor. .. I did replace the sensor.. kindof tough. Blind reach and all. But it didnt seem to help. Go and tighten all the electric wires you can reach. Even the red one at the firewall box on that side.

MY POST
I have a Taurus that had a BAD violently jerking transmission..
My trannie ran sometimes ok. for maybe 5 or more miles. (intermittent)
After AAMCO told me a new Trannie was needed.
I figured intermittent was the key to it NOT being the trannie.

I found that the VSS is controlling the computer to shift tranny and cruise control.

The solution was proubbly a bad VSS.OR

Bad battery connections.
My terminals were corroded.
Bad battery to RELAY box (firewall driverside red cable).
My nut was loose to relay box.
Dirty or connection to VSS on VSS sensor. 2 pins dark green /orange yellow.
My connection pins were black and not shiney. Hard to reach just under exhaust manafold.
Dirty VCC ground.
My VCC connection ground (green screw with 2 orange/yellow 1 black wire) on wheel well justback from beside the battery.. Cleaned but looked ok.

Worst connection was at the relay box large red connection nut was movable by hand but almost snug, but I cleaned them all first and the problem has gone away. For now. (50miles) never made it 5 before.

NOW (9/2006) NO PROBLEMS 1000Miles


GOOD LUCK

IT WAS WAY TO EASY TO FIX.. .hope its the same as yours.

I will give that a try as well. It would be great if I could fix this without spending a dime.

[GreasyBob]

I managed to extract the VSS today, and replace it. It didn't make any difference at all. Just for kicks I tried getting the diagnostic trouble codes from the computer. I got three codes (i think) 539 and 452. The last being the "insufficient input from VSS" code. I have replaced the VSS, and checked all of the connections I could find. Does anyone know of anything else I can check for that would cause that code to appear?

The actual numbers it gave were:

539 539 1 452 452

Does that look correct, or should I rerun the test?

[shorod]

Have you cleared the codes since replacing the VSS, driven the car, and rechecked for codes? The code you may be getting for the VSS could be a history code, but not a current code since you performed a KOEO code check.

-Rod

[GreasyBob]

Originally Posted by shorod

Have you cleared the codes since replacing the VSS, driven the car, and rechecked for codes? The code you may be getting for the VSS could be a history code, but not a current code since you performed a KOEO code check.

-Rod

I drove it to test after installing the new VSS.

[shorod]

Originally Posted by GreasyBob

I drove it to test after installing the new VSS.

But had you cleared the codes first? If the VSS code was there from before replacing the code, just replacing the part will not cause the VSS code to disappear from the code history. So, clear the codes, verify the codes are cleared, take the car for a drive, check for codes. If the VSS code appears again, then you need to check the new part and inspect the wiring.

-Rod

[GreasyBob]

Originally Posted by shorod

But had you cleared the codes first? If the VSS code was there from before replacing the code, just replacing the part will not cause the VSS code to disappear from the code history. So, clear the codes, verify the codes are cleared, take the car for a drive, check for codes. If the VSS code appears again, then you need to check the new part and inspect the wiring.

-Rod

I only checked after replacing the part. I drove the car to test the new VSS. After that I checked the codes. How do I clear the codes?