On a few occasions my O/D "OFF" would flash. The overdrive is working fine, I read some info online and so I sprayed water near the outer sensor and checked tranny fluid. This happened on maybe 3 seperate occasions quiet a few months apart. The flashing stopped after doing the spraying and checking of fluid, great. Well, its been maybe 8 months and it has started again and this time spraying and checking fluid did not help. My truck is a 1999 F150 Super Cab. It has just over 76000 miles. I did a complete fluid and filter change a few days ago. I test drove and still flashes. I watched for when light would start flashing and it is usually after running for maybe 5-8 minutes and when automatic trans shifts its final gear then bam flashing starts. It is a steady flash not fast. Of course it stops when I shut off truck and restart, because it resets itself. I have used the ODB II and get back no codes. I have no hard shifting. Does anyone have any info that is helpful in this troubleshooting. Not sure if this is pertenant but for some time as well my mileage read out does not illuminate when truck starts all the time, sometime it takes a significant amount of miles and the mileage area will illuminate so the miles are visible, and also my wipers will come on by themself, maybe do 1 or 2 wipes and thats it. I have started my struck before and the wipers come on by themself and the switch is off. Crazy stuff but any assist would be greatly appreciated.

 

Two things you can check. One is the connection where the plug connects to the PCM. The other is the section where all the fuses are. What you are looking for is possible water intrusion and/or corrosion. It doesn't have to be a lot, but is usually enough to produce some weird problems.

 

Ok, this is weird. The milage not comming on is almost always just a cluster that has problems, but the wipers could be an indicator of something else going on.
I can think of 2 other things to check. One is all the grounds, especially the ones that go from the battery to the body and the body to the engine (this is usually never put back on or taken off and forgotten about), the other is the MLP sensor (neutral start/reverse light/trans range sensor) on the side of the trans. Take the connector apart and look for corroded pins or other obvious damage.
THe o/d light can come on for many reasons, but if it's not leaving a code, then the only way I know of to catch the code is to not shut the car off and read codes when it's on; it's rare that they do this, but I've seen it before.