From smooth to limp mode and P0700 code

KATfishing said:

That's awesome and very appreciated! I actually didn't learn of the other codes until last night. Also, after you posted I called the GM at the shop and went over the points you listed just to double check. He was great about talking it through again. Thank you! People like you keep me active on this forum.

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I ran shops for 35 years and can tell you that many people came in and said so and so shop said it is this or that. I asked how did they arrive at that. They would say they plugged in an "all knowing scanner" and told them in less than 5 minutes that this or that part needed to be replaced and was typically a parts store or a shade tree. I told the customer I would either replace that part with no warranty or I would do a diagnostic and show you what is wrong and why and then give an estimate. Your initial post did not have as much detail as I like to see so I questioned it and your history with the shop. I always ask a lot of questions and will double check as much as possible. That is why this forum is such a great source for help.


There was nothing worse than telling a customer that something needed replaced and then they ok'd it and it did not fix the problem. I hated that and comebacks with a passion.

I have an o8 denali xl AWD with 137,000 and im struggling with doing some preventive maint, ie tq convertor as it is a known failure and quite likely what went on your's. But the way you are going is assuredly the most reliable option with a 3 yr unlimited mileage GM reman trans. $5k is approx 8 months of payments if you bought a new vehicle. I do plan on doing the reman myself when it happens, i sure hope it craps in my driveway and not while towing the TT 1000 miles from the house!

thompsoj22 said:

I have an o8 denali xl AWD with 137,000 and im struggling with doing some preventive maint, ie tq convertor as it is a known failure and quite likely what went on your's. But the way you are going is assuredly the most reliable option with a 3 yr unlimited mileage GM reman trans. $5k is approx 8 months of payments if you bought a new vehicle. I do plan on doing the reman myself when it happens, i sure hope it craps in my driveway and not while towing the TT 1000 miles from the house!

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Thanks for your thoughts. I wish you all the best as you tackle those tasks. I purchased my Denali at 84K miles and paid for an aftermarket warranty (expired 20K miles ago) that I bought through a dealership at the time of purchase. It was a 45K/4-year term and I ended up coming out ahead on the warranty. It was pretty comprehensive, covering my axle seals, a front differential, fuel pump, wheel bearings, battery, lower ball joints, etc. The vehicle also had quite a bit of history available right through the Carfax report. I knew it had been cared for. I've kept up with the maintenance schedule on fluids, plugs/wires, etc. I continue to do as much as I'm comfortable/confident with myself to save money... brakes, pulleys, belts, manifold clamps, EVAP parts, like updated vent valve assembly, new headlight assemblies, seat heater, etc. I never had problems with the transmission, so that was unexpected; although it had enough miles on it so not a major surprise -- just a big downer. The warranty on the reman trans gives me some peace of mind. It's the biggest single expense this vehicle has seen. I'm hoping it breathes some life into the vehicle so it can keep on going... hopefully without anything major again in the next couple of years. We still have 8 months of payments left on the vehicle (about $4,200), so putting a reman trans in makes sense, and continuing to drive it versus starting over with another vehicle. Plus, it's just a really great ride.

Just reporting back to this thread that I received my vehicle back yesterday, and the remanufactured transmission shifts wonderfully, as expected of course. The "adaptive learning" will take a bit, but it's quite smooth right out of the shop. My shop is "GM preferred" and the remanufactured transmission is from GM. The powertrain warranty is 3 years/unlimited and a GM certificate of warranty was provided for the glove compartment. They replaced all cooler line piping. The CV axle is also an OEM part with lifetime warranty on part and labor. Now i can pick up where I left off a couple of weeks ago and complete my brake job with the rear rotors and pads -- then it's a wrap for now (and hopefully quite a while)! Time to get back to enjoying my ride.

Great. Glad it all worked out.

This has been a great blog and I'm still curious about what else might lead up to this problem. I have an 08 Denali awd with similar symptoms, however they have been building for 3 years now. The trans began struggling with getting hot under load going over passes. Then it started getting hot during daily driving in the vegas heat. It eventually started losing gear sliding when hot, and eventually going into limp mode but would reset after pulling over,shutting it off to reset and running to cool off. As time has gone it is doing the same but at lower temperatures. Now just at 160f I run the risk of hitting limp mode and having to pull over. This doesn't happen so long as I'm cruising at freeway speeds and don't hit traffic and definitely cand drive it in the heat. Got a quote just to Crack it open at 5k! Seems like the older reputable shops here are now a rip off and the others just specialize in used units. If I had the space I would rebuild it myself but I'm not seeing any kits that include everything like sensors.

Welcome to the forum.

Do you have friends to get a recommendation from?

OR VietVet said:

Welcome to the forum.

Do you have friends to get a recommendation from?

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I had a private mechanic that doesn't to trans work much look at it, he suspected a solenoid issue. Said he could see some poor looking O rings? However said if we replaced it we would need a special cal he couldn't do so we would have to find someone to come out and do it at the house if possible

It seems to be an unfortunate thing with the early model 6 speed transmissions. I bought a 2007 Denali years back that had a trans warranted right at 100k. I bought it at 160k, drove problem free til I sold it at 227k

Fast forward to where I missed that body style snd bought a 2008 Denali again. This one had the trans replaced at 130k. Going good so far. It did get quite hot (210F) climbing some 12k peaks in CO. I took a proactive approach and let the truck idle for 15 minutes with the hood open to get temps back in the safer zone. Fingers crossed so far.......

B-train said:

It seems to be an unfortunate thing with the early model 6 speed transmissions. I bought a 2007 Denali years back that had a trans warranted right at 100k. I bought it at 160k, drove problem free til I sold it at 227k

Fast forward to where I missed that body style snd bought a 2008 Denali again. This one had the trans replaced at 130k. Going good so far. It did get quite hot (210F) climbing some 12k peaks in CO. I took a proactive approach and let the truck idle for 15 minutes with the hood open to get temps back in the safer zone. Fingers crossed so far.......

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210* is nothing for a 6L80E. 175* is the "normal" warmed up temp. The dex VI fluid
is synthetic. As long as you're not consistently running over 210-220* just cruising around you are just fine.
While towing, 210* is normal