Hi Guys, I have a 1999 5.4L 2WD with a few issues. Wanted to reach out for your thoughts on the following:

Issues/Background:
1) Overdrive light will begin flashing around 60-70MPH - does not flash at lower speeds. OD light stops blinking upon restart and only reappears around the same speeds.
2) At approximately 45-50MPH transmission seems to up and down shift every 2 seconds; RPMs "slightly" go up and down at the same time.
3) Scanner (non-ford specific) pulls the following codes (P0741) and (P0136)
4) I tried cleaning the O2 sensor in question regarding (P0136) but it did not clear code
5) I did reset codes via scanner - but they all came back after driving ~10miles
6) Next, I disconnected battery - but all came back again after driving ~10miles
7) Not sure what to check with regards to P0741, but I do know that transmission fluid is not low and does not appear dirty

Any thoughts on what to check next? Many thanks in advance for any feedback!

 

Solenoid in the transmission most likely needs to be replaced. Flashing OD means an electrical fault. At 60 mph your TC is locked.

If you're OK with working in a transmission, this is a DIY job. A transmission shop would be able to do a diagnosis and give you a quote (my guess would be $400-500).

For your O2 sensor, I would start by replacing it/both of the upstream ones. 100k is about when they start to go.

 

Thanks Tackle. she has 215K on her. I recently acquired the truck from a friend (who has no history on it)