MDMIKE

I thought I would start a thread to "pay it forward" for all the research and knowledge I've gained on here over the last week or so, and share my boneheaded story about getting my "limp mode" issue fixed. I read a lot of threads on here while researching my problem and they were all very helpful, but it seems like once someone gets their issue fixed, they drop off without letting folks know what the final issue was.

:Warning: This will be a long read! Your beverage of choice might be necessary to get through it

Truck in question: 97 12v 4x4 with a full Goerend Bros. 47RE automatic transmission. The truck has 169k miles on it, and the trans has about 50k. Truck is used for tow/hauling duties, along with snow plowing. I drive it to work occasionally, but most of the time the truck is used pretty hard, then put in the garage. Rode hard/put up wet so to speak.

Back story: We got a pretty nasty snow storm in the North East here last week and I plowed snow for close to 24 hours straight. Transmission worked perfectly the whole time, and my transmission temperature gauge never exceeded 180*. I had a fluid flush/filter change about 2 months ago (maybe 700 miles or so). I had gotten the truck hung up a couple of times while plowing and had to rock it back and forth a few times to get it unstuck, but other than that, I can honestly say the transmission was not "abused" while plowing.

Symptoms: Heading home from plowing at work, I realized the truck was starting out in 3rd gear from a stop. I could manually shift the trans down into 1st gear, and shift to 2nd and 3rd with the shifter, but up-shifts were very "abrupt" unless I completely backed off the go pedal between shifting (kind of hard to do with a bed full of snow and an 8' plow on the front and still keep forward progress). At first, I noticed that if I came to a stop with the truck in "drive" and I had to sit for a second, sometimes I could feel the transmission downshift itself into 1st after a few seconds of sitting there. In fact, the first time it happened, I thought the guy behind me hit my bumper. That symptom disappeared after a day or so, and the transmission would make no attempt to downshift at all. The other thing I found weird was after the truck had been shut down and restarted, I could put the truck in drive and it would shift normally for its first run through the gears, but after that it would go back to starting off in 3rd gear again. I didn't experience a "check engine" light either.

Research: So, I jumped on DTR and started digging. That is when I learned about "Limp Mode" and the struggles that other members have had with getting it figured out. After trying the easy fixes others had suggested, such as checking for blown fuses and swapping the relay in the fuse box under the hood, the culprit that stuck out the most to me was the governor pressure solenoid and relay in the valve body.
At this point, I will fully admit to being lazy, and I took my truck to my local transmission shop to have the work done. I dropped my truck off the evening before I was scheduled to have it worked on, and the owner called me at 9 am the following morning and said, "Remind me what I'm supposed to be doing here again, because this truck drives great!" I explained to him what it was doing, and how I had come to the conclusion to have the governor pressure solenoid and relay replaced. He agreed with my symptoms, but swore to me the truck was shifting fine for him, and he didn't want to take my $$ for "fixing something that wasn't broken".
So I basically talked them into swapping the parts out for me, and doing another filter/fluid flush even though he thought the fluid still looked great as well. That evening I went to pick the truck up from the shop, and I didn't even make it out of the parking lot before the truck went back into "limp mode".

More research: Back to DTR I go. I came across everything from Throttle Position Sensor problems (I replaced that a couple months ago because I thought the truck was getting lazy going into lockup), to Vehicle Speed Sensor issues, Crank Position Sensor problems, ECU reading too high of governor pressure voltage (fix is a 100-150 ohm resistor on the orange wire on the middle plug to the ECU), chafed wiring harnesses, etc. The one that caught my eye was to check the main wiring harness plug for the transmission where it plugs in from the top on the driver's side of the case.

The fix: So I crawled under the truck, and wiggled the plug around a little. It seemed plenty tight, but I could tell there was some debris caked up around the plug. Even with a decent drop light, I had some trouble seeing exactly what was going on up there, so I removed the **** and boot from the transfer case shifter and inspected it from the top. Sure enough, there was so much crud and garbage packed in around the plug, it made it seem like the plug was in tight. I hosed the area down with brake cleaner and a ton of junk came oozing out of indented area where the plug is. When I went to unplug the harness, the entire female side of the plug broke off in my hand. The only thing left were the "prongs" sticking up out of the transmission, and nothing else for the chassis side of the harness to clip into.

Back to the transmission shop! (Yes, I know, lazy once again. But I was guaranteed results in 1 day and I was getting fed up with the truck at that point). They replaced the valve body wiring harness for me.

Results: It might just be me, but I think the truck drives better now than it did before. Lockup seems to happen a few rpm's sooner, and is much more predictable. The truck still has firm shifts through the gears, but it seems "smoother" for lack of a better term. The delayed downshift problem is gone as well.
The area machined into the side of the transmission case where the wiring harness plugs in is a perfect place for junk to collect over time. (My driveway is gravel, and I swear 1/2 of it was stuck up there next to the plug ) Even if the plug hadn't broken when I tried to unplug it, I could assure you that there was moisture in there causing corrosion of the "prongs" that stick out from the valve body side of the harness.

So, if you're having "limp mode" issues with your 47RE, make sure to check that plug before you do what I did, and throw good $$ at the wrong parts!

patdaly

Thanks for the post, always good to hear a success story.

I guess that's why the connector and short wiring is available from the aftermarket, must be more common than I would have thought.