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First I noticed the electronic display of "PRND321" is going in and out, while the rest of the lights on the dash work fine. 2nd, I noticed when the PRND321 display goes out, the transmission will not shift out of or above 1st gear. Naturally, I assume this is an electronic issue and not just a dash fuse. I'm assuming there is a Transmission Control Module of sorts that send signals from the engine to the tranny on when to shift. Can anyone point me in the right direction here to begin troubleshooting. Other than that, never had any tranny issues, no slipping, hard shifts, etc.. fluid has been changed regularly. 119K miles on the tranny. Thanks for any help!
Nice looking van and the tires look awesome on there. The 4L80E is a great trans and it sound like you have an intermittent problem so I think you are correct with looking for electrical problems. On a 2000 model there is no transmission control module like on the newer ones. It should all be housed in what they called a PCM or powertrain control module with handles the engine and transmission operations together. I would start with basic stuff like checking grounds and main cables. Not sure what climate you are in but these vans seem to rust alot in northern climates and there are several grounds on the chassis that can be compromised causing weird problems like this. There may be a main ground near the starter between the engine block and the frame which ties to the negative battery cable. These are prone to failure due to rust and even if they are not broken if they are green in color they need replacing. This may or may not be present on yours as I am referencing the 2003 up models with the LS GEN 3 and GEN 4 engines but its a start. Also not a bad idea to have the alternator checked out. If all that looks good, I would check where the trans harness plugs into the transmission. At 20 years old there could be some corrosion or the connector could be cracked causing connection issues with the PCM. those are my ideas where I would start. Id also make sure none of the body grounds inside the van got messed up when the van was modified inside.
@Garner Ames thanks for the advice. I am in Colorado, so cold and snowy here right now. Couple of things to checkoff. 1) I replaced the alternator a few months ago, so its almost brand new. 2) I was pretty diligent about the body grounds when renovating the interior, but will double check.
I think I'll start by locating the PCM harness and checking for cracks/wear, then also all the other major grounds. I'll have to look for a good guide to all the grounds in the van somewhere on this forum. Thanks!
No problem. I would just go over the major grounds at the chassis and engine block. Those would be most prone to rust issues. Believe it or not, I drove my van in the snow just weekend in central texas and almost got it stuck on a hill on a dirt road covered in three inches of snow. Im liking those tires you got on your ride. Do you like them?
Yes, I've since updated the tires to some Sumitomo Ice Edges for the winter(not pictured) as its definitely needed in CO. Glad you were able to survive the snow in TX, that's a rarity. The pictured tires are Toyos that I keep for the summer and are great, Doesn't hurt to have a 3 inch lift on the body, too!
Going to clean up PCM connectors and wires with electrical contact cleaner tonight before the next big storm comes in! Still need to find a good guide on where all the major body grounds are that I need to check. I'm a lot more familiar with Jeeps unfortunately. I can certainly identify the ones are the battery and probably some more obvious ones, but working in the engine bay on the van vs the jeep is night and day... funny really.
both sets of tires are 31's and rub a tiny tiny bit on the frame up front when turning the wheel all the way, but help huge for anything offroad since she's only 2wd.
If you go to gmupfitter.com, there are electrical manuals for the Express. It has circuit schematics, and detailed drawings showing the routing of every wiring harness, each connector and each ground point. Great reference.
Transmission Acting Up
