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4l80e shift solenoid b stuck in off position code

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NiceTruckOldMan

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I recently purchased a 97 c2500 that had been sitting a few years. The transmission had been rebuilt less than 5000 miles ago but there is an issue with getting stuck in 3rd? gear, especially when going up mountain passes and won't go to overdrive or 4th even coming down the mountain. It's also gotten stuck just driving in town at low speeds but turning off and restarting the truck gets it right again. Also have an issue of rpm fluctuating when cruising around 70 like it's trying to shift? Any input is appreciated.
 
Welcome to the forum @NiceTruckOldMan update your signature with the details of your truck, things like year, make, model, engine, and trans, along with any work that has been done including upgrades and modifications. this will help us all when diagnosing issues, we can see what you have and have done and it shows up for us each time you post.

your truck has ether a 4l60e or 4l80e depending on what engine you have. things you want to check... any codes on the PCM, the SES light might not be on but some tranny codes can still be present with the light off in the dash. did this issue just start or has it been like this since the trans was rebuilt? is the tranny fluid at the full mark when the engine is running and fully warm? what color is the fluid and does it smell burnt?
Does the speedo work and is it showing accurate compared to the GPS on your phone? How harsh are the shifts from 1st, 2nd, 3rd, etc...

check to see if your TCC is working. TCC= transmission torque converter clutch. this is the lockup which should be working in both 3rd and 4th. an easy way to check is to get the truck up to cruising speed around 55 mph on a mostly flat road.. watch your tach for the RPM while gently applying the brake just enough to turn the brake lights on all the while not taking your foot off the go pedal maintaining speed. you should see about a 200 RPM increase momentarily until you take your foot off the brake pedal. you should also slightly feel the TCC release, almost feels like a shift but much softer. If what you are experiencing as fluctuating RPM stops during this test, this means the TCC is trying to engage but is having issues.

while you are performing this test, verify if your cruise control works.

Next park the truck and set the parking brake or block the tires, crawl underneath on the drivers side and look on the side of the transmission, you should see a large round connector with several wires in a loom. it should have a pair of tabs, one on each side to squeeze on and pull the connector straight out from the trans. look for the inside of the connector for trans fluid leakage. sometime fluid will seep from this area an cause a short on the pins. also look for any corrosion or burnt connections. you can spray brake cleaner into them to wash out any fluid and debris.

If you find any fluid or debris, clean it and go for a drive checking for any improvement.

report back here with your findings and answers to questions along with further details on your truck. we are all here to help :)
 
Thank you, I tried some of the things you said, Cruising and tapping the brakes I got mixed results, rpms went up, rpms stayed the same and rpms went down on different trys. I'm thinking I didn't perform the test right. I also removed the wiring connectors and they were quite dirty and I sprayed them out. As far as I know it's been this way since rebuiult and not driven much last 5 years. It actually felt like it was slipping pretty hard with rpms going up but not into another gear it seemed last night. I slowed down below 70 like a civilised driver and it cleared up. Then it acted up off the highway and got stuck in second, which I'm pretty sure has been the gear it's been sticking in. It did that on the way to town as well getting to the top of the mountain pass and I reset it at the next exit.
 
Given you are getting both codes together, I would put my finger on a wiring issue, but can be an issue in the trans as well. is there any warranty on the rebuild that was done? even if it was done a few years back, since it hasn't been driven over 5k miles since the rebuild, I would to talk to the shop that rebuilt it and see what they would work out with you. at least cover that base before diving into the trans too deep. we can help diagnose some of the issues or at least eliminate some steps, but if that shop will work with you and you open up the trans, they might not want to work with you.

when did this issue start happening?
 
There's definitely no warranty on the work that was done. As far as I know it has been a little messed up since the rebuild. My friend that put the scan tool on it thinks it's probably a pressure issue due to contaminated fluid.
 
If there is a possibility of fluid contamination, I would first start out by dropping the pan and replacing the filter and fluid. the hard part about contamination is getting all the fluid out from the converter. it holds several quarts by it's self that can't be drained without pulling the trans.

once you drop the pan, pay close attention to the debris in the bottom and what's collected on the magnetic. take some photos and post up here for us to see.

what ever you do, do NOT take to a service place to have it flushed. that is a guarantee to kill the trans! you can pull one of the trans cooler lines from the radiator and drop into a bucket, have several quarts ready and a funnel. start up the engine and as the fluid slowly flows into the bucket, pour in one quart at a time keeping the trans from running empty. this would be about the only way I would know how to flush out any contaminated fluid. Others can chime in if there is a better way. IDK if the suction side of the trans cooler lines would "pick-up" fluid from another bucket.

FWI,,, use ONLY dextron III fluid. do not use dex 6 as it has been know not to hold up and is a thinner oil than the original dex 3. afaik Valvoline is the only MFG that still does dex 3 fluid.

what is it contaminated with??
 
Here's some more reading material on flushing. just be sure to drop the pan and clean it out along with a new filter before flushing. you want to make sure all the loose debris is not sucked up into the valve body or get a clogged filter.

To Flush or Not, 4L80E

What's involved in flushing the transmission? Is it really all that it's cracked up to be, or is it just a way for shops to get your $$$. How much does it cost on the 4L80E? How often should it be done?
www.thetruckstop.us

www.dieselplace.com

4L80E complete fluid flush

www.dieselplace.com www.dieselplace.com
 
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