My engine light on my 99 4.0 came on the other day after 2 days of heavy rain the check engine light came on (my wife was driving, so any subsequent repair costs will be blamed on her). The next day it was on in the morning, then went off for the rest of the day. It came back on this morning. Advance Auto told me it was P0740 code. Everything is running and shifting smoothly.

Other info that I'm not sure matters: P0470 TCC circuit malfunction (NO BUS) came up in the past few months, but hasn't been an issue since--if I bang the dash it goes away. I changed the transmission fluid/filter about a month ago.

Can you all give me some advice on where to begin trying to diagnose this?
Thanks,
Mill

You say it's shifting smoothly, but are you seeing problems with going into Over Drive, i.e., a drop in RPM once you've stabilized cruise speed?

Thanks, CCKen. I got cruising at 50mph on the way home tonight and RPM was stable at 1600. Is this what you mean?
Mill

I'd clean the cluster connectors to start. Banging on the dash is a pretty good sign they need it.

Thanks, Radi. What wires should I be checking for the P0740 code?
Mill

Here's some possible causes for P0740:

TPS DTC P0122 PRESENT IN THE TCM
TPS DTC’S PRESENT IN THE PCM
TCM DTC’S P1748 AND/OR P1749 PRESENT
INTERMITTENT WIRING AND/OR CONNECTORS
TRANSMISSION OIL BURNT AND/OR CONTAINS EXCESSIVE DEBRIS
INTERNAL TRANSMISSION

Your TPS may have gotten soaked, or the connectors near the trans dipstick (see pic), during the heavy rains

Was your ATF black-ish or smelled burnt when you changed it?

Try clearing the code by removng the battery negative post connector for around 30 minutes, reconnect, and see if the code pops up again.

Connectors: