Hello, I'm knew to the forum but have 23 years experience in the auto industry. My wife's 2017 Yukon XL is not throwing any codes, but the transmission was intermittently shifting hard into 1st when she increased RPM's (due to the false neutral situation). Once the vehicle exceeds 5 MPH is seems to drive as normal. Coming to a stop it's 50/50 if it drops into a false neutral. This comes 3 weeks after swapping the 5.3L with a 40K mile used one. I'm up to my ears after pulling the transmission twice. First time I upgraded the Torque converter, solenoids, check balls (including #1), pressure regulators, etc. The second time I replaced the L/R sprag, hoping it was the issue. I'm getting no codes but starting to worry it's a vehicle side electrical issue? That being said, it should drive even if the transmission wire is disconnected, correct? However, it doesn't move while disconnected...... pushing me toward an internal transmission issue. The wife and kiddo's have been riding with me for 3 months..... need help!
2017 Yukon XL 6L80 - False Neutral intermittent from stop to 1st gear
- Thread starter Ooos
- Start date
Welcome to the Nation.
Is your PCM/TCM tuned by any chance? The one in my 2011 Caprice was tuned and the tranny really shifted hard and also had a kinda drop to neutral when slowing down and would then shift into 1st which made it feel like I was getting rear ended. I put the tranny tune back to stock except for the TCC and it's back to normal. The tuner had maxed out all the pressures which made it shift hard in all gears. It still doesn't feel 100% but it works.
Other than that, I would suspect an internal failure. Could be the TEHCM has a bad switch or valve. Might have to bring it to a transmission shop. There are lots of things that can fail in this transmission and I have watched many teardowns of it on the YT channel Precision Transmission. He is very knowledgeable of this tranny.
Is your PCM/TCM tuned by any chance? The one in my 2011 Caprice was tuned and the tranny really shifted hard and also had a kinda drop to neutral when slowing down and would then shift into 1st which made it feel like I was getting rear ended. I put the tranny tune back to stock except for the TCC and it's back to normal. The tuner had maxed out all the pressures which made it shift hard in all gears. It still doesn't feel 100% but it works.
Other than that, I would suspect an internal failure. Could be the TEHCM has a bad switch or valve. Might have to bring it to a transmission shop. There are lots of things that can fail in this transmission and I have watched many teardowns of it on the YT channel Precision Transmission. He is very knowledgeable of this tranny.
It could be the TEHCM, it just seems odd 3 weeks after an engine swap. It's the one thing I haven't replaced. I had an old school, tranny guy do all the upgrades. I trust him, he's been working with me for 15+ years. Vehicle side vs transmission side is where I'm stumped. I've re flashed the vehicle twice.... so far. Tranny guy says it's a vehicle side issue, shop says its trans issue. I'm caught in between with no codes.
I appreciate the info. The symptoms (50/50 1st gear engagement, reverse working) match the work done per the diagram. The 1,2,3,4 drum, sprag, or speed sensor but all of these have been addressed. I'll dig deeper..... might be my grave.
MaroonMonsterLS1
Member
It ended up being an internal issue. I took it to a different transmission shop, after I realized my old transmission guy is getting too old. Pulled it three times, win for me (sarcasm)! Either way it's running great now.