Hey there. My dad picked up a very clean 04 4.0 4x4 this weekend and drove it 2.5 hrs home flawlessly.

During the drive, it seemed to completely lose overdrive, and was at 3000-3500 rpm cruising at 70-78 mph. He drove it like that most of the way with no flashing overdrive light. Whenever he turns the headlights on, the OD light flashes, but there is no difference in how the truck drives.

when the truck is restarted, the overdrive button on the stalk makes the light on the dash go on and off as it should, but once up to speed, it starts flashing again if the headlights are on.

it also has a firm 1-2 shift, and the previously mentioned lack of overdrive.

where should I start when investigating this?

Thanks.


update: my scanner shows a P0735 gear 5 incorrect ratio code. My research has taught me that 2nd is just 1st with OD enabled. It does shift into “2nd” a little rough, but it isn’t bad enough to rattle your teeth out of your head. Tranny fluid is pretty dark and does not smell like ATF at all. Should I start with a tranny fluid and filter swap and go from there?


update 2: Truck has overdrive for the first 10 miles or so but then loses it and the OD light begins flashing again. Seems electrical to my inexperienced mind.


Any help is greatly appreciated.