87k on the clock. Recently did a trans pan drop and filter change/fluid fill w/ATF+4 as part of a maintenance rodeo from this van sitting for umpteen years and barely being driven. Recently coming back from a 500 mile road trip, (which was probably the first time this van has been driven at highway speeds in several years) and lost overdrive/TCC engagement close to home thankfully. I did NOT adjust the bands as I didn't know that was a thing or possible until researching this issue.

Here's where I'm at and looking for anything I may have missed before dropping pan (again) and replacing the OD/TCC solenoid and adjusting bands:

• 1-2-3 shifts are spot on w/no issues going up or down
• Speedo and engine temp gauges are working just as they were before. Speedo correct +/- 2mph and coolant temp gauge correct. Coolant temp is ~195* as is should be (verified with infrared thermometer at radiator).
• Fluid level check shows level correct (vehicle running, up to temp, in Neutral, and on level surface)
• Back probed 3-pin connector leads near trans bell housing. Multimeter + lead on blue wire and - lead on orange wire w/white trace. While driving, PCM is commanding OD/TCC solenoid via grounding the orange wire w/white lead as evidenced by ~12v at cruise at speeds of ~40-45 mph
• Wired in a toggle switch with one lead on orange w/white trace wire and other to engine block. Toggling switch on in third gear above 45mph results in no change, re: vehicle does not shift into overdrive.

 

Might be a bad connection on the three pin connector..... If TCC and O/D are both out, I would suspect the power feed. It would be extremely rare for both solenoids to fail at the same time.

 

To be fair, I'm not 100% certain the TCC solenoid is out because I was under the assumption since I wasn't hitting OD then the TC wouldn't achieve lockup. At least no vehicle I've ever owned operates like that. I guess tomorrow I'll try checking voltage at the connector and then also trying the toggle switch on the TC side of the wiring to see if I can force it to lock in third gear.

I did try hitting the trick by hitting the brake slightly with my foot on the accelerator a few times and didn't hear the RPM change in third gear but it was also pretty loud driving around with the doghouse removed and would have been hard to distinguish a slight drop in RPMs that unlocking a converter would cause.

I will report back findings tomorrow. Time to get creative with some test wires...

 

There is some debate on that topic as well. On both my trucks, (one a 46RE, the other a 47RE.... essentially the same trans, just some heavier duty parts in the 47...) It will shift 1-2-3-TCC-O/D. If you hit the tow/haul button, it just disables O/D.

 

Update: So after further testing, the TCC is engaging via PCM command in third gear. Verified it by watching voltage on multimeter and closely listening to RPMs while in third. It is engaging...and also disengaging when applying brakes while foot still on accelerator. It's just difficult to distinguish by sound alone with all the noise with the doghouse off and going down the road. I also had the toggle switch hooked up on the TCC wiring side this time and was able to switch the TC lockup on and off a few times to get a feel for what it feels/sounds like. So @HeyYou , this appears to confirm what you stated about the 47 series trans shifting 1-2-3-TCC-OD. Seems the 46 is the same.

I also tested for voltage on center wire directly at the connector KO/EO and had voltage, so I'm going with a bad OD solenoid as diagnosis. New solenoid pack, fluid, and filter/gasket will be here Friday so I'll report back once I get it buttoned up and hopefully be able to report success.

 

Sounds like you have it dialed in. Definitely let us know the outcome.