I need some help with a '94 Taurus wagon. It's got about 110K miles on it. It's the basic V6 engine and transmission. It's been well cared for for the most part. I had the fluid and filter changed about 30K miles ago. The transmission has started doing something odd. It seems to stick in third or fourth gear. It doesn't seem to be slipping and it's not noisy or clattering. The mechanic told her that when it goes into drive, it goes straight to "high gear". They don't know what the trouble is. She didn't remember to ask about the codes. Given the symptoms, could it be a sensor, solenoid, or TCM, something worse?

 

Hello and good day to you:

First, is there a CEL (check engine light) on? If so what is it doing>soild or blinking?
Second, Yes it could be a Sensor, Solenoid...
Vehicle Speed Sensor (VSS)

The Vehicle Speed Sensor (VSS) is a small signal generator that is turned by a gear inside the transmission assembly. The Vehicle Speed Sensor produces 8 pulse per rotation which a stock computer assumes 8000 pulses per mile. The Vehicle Speed Sensor (VSS) is a variable reluctance sensor that generates a waveform with a frequency that is proportional to vehicle road speed. When the vehicle is moving slowly, the sensor produces a low frequency signal. As the vehicle speed increases, the sensor produces a higher frequency signal The Vehicle Speed Sensor (VSS) supplies this signal to the components that require vehicle speed information including the speed control amplifier for cruise control equipped vehicles and computer. The computer uses the VSS signal for emmisions contol programs and speed limiters. The emmisions programing can cause a manual transmission vehicle to stall out while decelerating if no VSS is used.

[/align]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 (both are synonomous names), and it is 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. Let's hope that isn't your problem.