Mechanics

NOT SHIFTING

1999 Ford Taurus

Transmission problem
1999 Ford Taurus 6 cyl Front Wheel Drive Automatic

I have a 1999 taurus with 129,000 miles on it. The car had been running fine, I never abuse the car.
I changed the engine oil in the car the day prior, I have always changed it my self. I Backed out of the driveway the next morning to leave for work, the OD light was flashing on the dash, I put the car in drive and proceeded down the road and the speedo wasn't working. I drove about 12 miles, the car seemed to be shifting mostly normal, I stopped at a stop sign, put the car into park and shout off the engine, I restarted the car, the overdrive light had gone off, but the car wouldn't shift out of first gear. I nursed the car home at 15mph, shifting the trans from 1st, to drive, to Od and nothing really made a difference. I got the car home and parked it for about 5 days.
I decided to start the car and see what it would do. I backed out of the drive, all seemed normal. I proceeded down the road about a mile and a half, evertthing worked normal, except the service enging light came on. Two hours later I started the car, backed out of the driveway, and the speedo wasn't working again, and the car wouldn't come out of first again. SO, I had my neighbor who is a mechanic bring over his code reader, the car had a PO500 fault, " speed sensor malfunction". So I replaced the speed sensor on the transmission, on the right side behind the motor mount. Unfortunately this didn't fix the problem. I know transmissions don't just break in the driveway, so I don't think it's a major mechanical problem. Could a abs wheel sensor cause this? The right front brake hose had collapsed and overheated the right front, melting the abs wire, yet the abs light hasn't come on. Any help would be GREAT! Thanks, Jason
Avatar
Jabone39
September 12, 2010.



It sounds like the problem still lies with the vehicle speed sensor. Have you checked wiring to make sure that everything is connected and there is no damage to it? Have you tried a different speed sensor?

I replaced the sensor with a new one, I also checked resistance on the one I took off, and from what I could find online, there wasn't anything wrong with the one I replaced. I will however check the wiring.
Could the problem be in the ABS control unit?
Isn't there 2 sensors on the transmission? An input and output?
One of the answers I got from a ford tech at another web site said a bad wheel sensor could cause the transmission to go into " limp" mode, I don't really see a relationship with the abs system and the transmission.
I'm racking my brain here, thanks.
Jason

Tiny
Jabone39
Sep 13, 2010.
Believe it or not, he is right. The transmission (limited slip or traction control) works together with the ABS. So what he said is correct.

As far as two sensors, here is what I found.

There are to speed sensors in the Taurus AX4N or AX4S transmission. One is called a TSS or Turbine shaft speed sensor, located on the body of the transmission cose to the driver's side, and the other is called either a VSS, vehicle speed sensor or an OSS Output Shaft Speed sensor and are located on the passenger's side, down behind the engine on the top of the output shaft housing of the transmission.

The PCM uses information from both sensors as well as other inputs like MLP(manual lever position) sensor, which is the PRNDL position sensor, calculated engine load(using throttle position and Mass air flow information to calculate), engine temperature, and input air temperature to make deccisions about how to shift the transmission. The Speedometer uses the signal from the VSS alone to determine and display vehicle speed. IT would seem likely that if you have a non-operational speedometer, poor transmission shift performance, and an inoperative cruise control, that the VSS is your culprit. Keep in mind though, that anything that prevents the VSS from spinning could also be your problem. THere is a VSS drive gear in the transmision, that is driven by another internal gear. Both those gears are plastic, and they do break sometimes. The probem is that the primary gear in that chain of gears cannot be replaced uness the entire transmission is disassembed

If I pull the trans pan, should there be evidence of the gear failure in the pan?
Also, why would it be intermittent if the primary gear failed? Seems like broken is broken, not sometimes it works, and others it doesn't.
Thanks again
Jason

Tiny
Jabone39
Sep 13, 2010.
Before pulling the pan (chances are you won't see anything from a plastic gear) check the TSS.

Alright, I've checked all the wiring and related connectors, nothing seems to be the problem there. I haven't checked the TSS yet (not sure where it is yet) I let the car sit for a week, and today I thought ah what the hell, I'll take it for a drive again, and see what happens. The car ran perfectly normal, shifted smoothly through all gears, cruise control worked, after about 8 miles, I slowed for a stop sign, proceeded and as I pulled away I felt a funny shift, the speedo stopped working, the OD light was flashing again, and the cruise didn't work again. So my question is, would a primary drive gear for the VSS cause this intermittent problem like this one? A missing tooth on the gear or something? I don't think it has anything to do with the trans getting warm, because this happened first thing in the morning before with a stone cold transmission. Should I be looking else where? I really believe it's an electrical problem, but I don't really know much about automatic transmissions. Thanks again.

Tiny
Jabone39
Sep 21, 2010.
I would be checking the vehicle speed sensor if you ddint replace it already. If you did take and do a pin to pin test checking resistance from connector at sensor to the harness on the PCM wiggle the wires too to see if you can cause the resistance to change by doing that. Do that for each wire on the speed sensor. Is it a 2 wire or a 3 wire sensor by the way?

Intermitten faults are tough but if you stick with me we will get it.

Blackop555
Sep 27, 2010.
I will give that a try, just have to find where the pcm is located, I have a chiltons manual so I should have a wiring schematic. The sensor is only a two wire by the way. I'll be in touch. Thanks again.

Tiny
Jabone39
Sep 28, 2010.
If you cant find pcm let me know. Make sure you get the resistance checks on those wires and make sure you wiggle it while testing the wires. And I mean wiggle all of it.

Also dont jam something inside the connector to get the pins. Make sure it fits good. Also check for corrosion on the connectors or the wires to be loose in the connectors or signs of a terminal in the connector that is pushed out or loose.

Blackop555
Sep 28, 2010.
I checked the wiring harness, at the ecm, I even removed the speed sensor again, I noticed some corrosion on the plug that attaches to the sensor down inside the plug, so I used a really small drill bit to clean it up, then I put some dielectric grease on the plug, used a VOM on the wires at the ECM moved around the wires, I got no infiinite resistences. I put it all back together, the only thing that has changed is now it seems to be even more intermittant. I also noticed that the speedo dosen't just quit, you have to come to a stop, then take off and the the speedo won't work, so while your at speed, everythings fine. Man I've about hadit with this car. Thanks again.

Tiny
Jabone39
Oct 4, 2010.
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