I have a 1997 F150 rear wheel drive with 4.2 liter engine. My overdrive light on shifter blinks after driving a short distance. If I then shut off the engine and restart the light will stay off longer. I took it to the transmission shop and they test drove. They told me that the transmission had no fault codes (even when light was flashing) and it test drove fine shifted in all gears. They determined that the unit on the side if the transmission was bad (they called it a “prein”???) sending incorrect info causing the overdrive light to flash.
They want $300 to fix, can anyone tell me what the unit on the side of the transmission is, would that be the problem and how hard to replace???

 

I don't understand why there are no fault codes. I assume they have a capable scanner?

Not a clue what they mean by a "prein".

 

Very well equipped transmission only shop. Because there are no codes they said the problem is the unit on the side of the transmission

 

I assume you are referring the Manual Lever Position Sensor "MLPS", which is the Ford term. GM refers to the part as a "PRNDL" switch.

Both names refer to the same part which tells the PCM which gear selection the shift lever is moved to.

 

Would a malfunctioning “MLPS” cause my blinking overdrive light. How hard is it to replace???

 

Easy to replace - it may just need adjustment. It's also the neutral safety switch. They are about $40 plus shipping from rockauto.com.

Don't have a clue what would cause the light to flash without setting a code.

 

Is it more than a neutral switch? I have no issues starting the engine, does anyone know if that would cause my blinking light

 

It's both a neutral safety switch and a transmission range sensor. I have NO IDEA what would cause a blinking OD light if there aren't any codes.

Take it to a different shop - see if THEIR scanner pulls any codes.

 

My blinking overdrive light never comes on when the engine is first started. Once it does come on, if I shut off the engine then restart the light will be off?????? Could it be some type of short, would shorting out or grounding out of the wires to the overdrive switch cause this???

 

you need a scan tool that will read pending codes AND stored codes. It also needs to be able to read Transmission codes.