yoshgixxer

iTrader: (74)

01 1500HD with 6.0/4L80E, trans shifted perfectly fine yesterday, went to jump in this morning to head to work and it wouldn't shift into OD. 1,2,3 shifts perfect, dosnt act weird and dosnt slip. Also noticed trans temps are oddly low. Like 150-160deg tops, always hung around 210 before. Any ideas on easy things to check before I go and yank the trans??

Thanks!

wht/73

So it's no 4th and no lock up?

yoshgixxer

iTrader: (74)

Correct, runs just like a TH400 lol

yoshgixxer

iTrader: (74)

Well would it lock up in 3rd even functioning correctly

clinebarger

Codes? Physically check with a scan tool.

Is 4th being commanded?

Low AFL pressure can cause a no 4th condition, But usually a drop out of 4th Hot, Low AFL pressure also affects line pressure, Are the shifts soft?

A broken 1-2 shift valve spring can also cause a no 4th condition.

I'm leaning toward a electrical malfunction because it happened suddenly with no symptoms leading up.

yoshgixxer

iTrader: (74)

I'm going to have truck scanned today to see what ECU is telling trans to do. 1-3 shifts feel exactly like they always did.