Hey gang. My truck decided it doesn't want to go into overdrive anymore and I'm looking for solutions.
For background: Recently got back from a road trip through Yellowstone. Wasn't towing anything and the truck wasn't loaded down by anything too heavy. A few times i noticed engine temp in the 230 range but it never overheated. once we got back to the prairie I checked the trannyfluid and it was quite a bit burnt. It had been checked before the trip and was fine before we left. I resolved to take it easy on the way home and drop the pan when we got there. A couple hundred miles later the truck started having some slipping issues between OD and 3rd. I shut off OD and nursed it another 250 miles home. By the time we got there the truck was also slipping before take off, but held gears while driving without issue.

Thinking this might just be a fluid issue, I drained the fluid and it was now black. left it to drain overnight and got about 6 quarts total out of the truck. refilled, and I was no longer having issues going into gear at take off. I drained the fluid again (still wasn't red due to the excess in the system) and swapped the filter before refilling again. The truck is now behaving normally, but will not go into overdrive at all. The fluid still isn't true red yet.

Wondering if I should try a manual flush or take it to the shop? or just drop the pan again and thoroughly clean the valve body. The transmission was rebuilt 80- 90k miles ago, the overdrive unit was rebuilt 5k miles ago. Thanks in advance.

 

If you are thinking about flushing it, don't. You might just as well rebuild it instead, as that will likely be needed shortly after the flush.

Change the fluid again.

Is the O/D Off lite on? Trans temp lite in the dash? Have you gotten rid of the check valve in the cooler line yet? I HIGHLY recommend that you do, if you haven't already. Might also consider a trans temp gauge.

Any codes?? (won't necessarily turn on the lite, check 'em anyway.)

 

cycled the OD, and it works like normal. No lights otherwise. I haven't done the check valve yet but will try that. Only code is a cylinder 7 misfire I've been fighting with.

 

Still won't shift into O/D though? Wonder if the PCM thinks the trans is too hot.... It the PCM requests overdrive, and doesn't see the RPM drop, it *should* set a code.....

 

Not seeing anything. No change in RPMS, no CEL, no instant codes if I check while driving...

 

Can you see if the PCM is even requesting O/D? Or if the PCM currently sees it as disabled?

 

Is there a way to check that? I can read raw data off the OBDII port but wouldn't know what to look for

 

Depends on what scanner you are using. The high-zoot fellers should have an option to show data (while driving), and you just scroll thru it and find what you want. If you have software for your laptop, I have discovered that they don't have all the process ID's implemented, though they can still read them.... but, I have never been able to find a list of just what the PRIDs are, and what format the data comes in......

 

My scanner is an OTC, which is low end and limited. I use the Torque android app mostly

 

I have no idea if that will tell you or not..... Snap-On MTG 2500 should, (or better) if you know someone that has one.