hi guys i have an el falcon with a 4 speed auto which is currently giving me dramas. it seems to be ok when first driving when all of a sudden either when you stop or whilst driving it selects 2nd gear and stays there (limp home mode). when i stop the car for a while and i go to strart it again it seems to be fine again for a while then it will do it again, and some times not at all. any ideas? i thought of changing the filter first to see if that works but what else can i look for.

check oil lever/colour, service the auto (full flush with atleast 20L of ATF , and maybe look at the solenoids?

Check for logged fault codes in the computer, but do you ever have any issues whatsoever with the speedo dropping out? It seems when they pick up a few bad readings from the speedo it triggers limp home.