I have a 2009 2LT 2.4 4T45 auto that slips or pops out of 4th gear but, not all the time. I can drive for a couple days and it works just fine then, I drive about 70 miles to work and about 55 miles back home when it slips or pops out of 4th. I have to limp it home in 3rd. This has happened a couple times so I started driving my truck to work while I look into the issue. Last Saturday I took the car out with a scan tool attached to see if I could get any codes. there were no codes stored before this issue. The car worked without a single issue. I drove it to work for the first 3 days of this week with no issues until Wednesday on my way home with about 15 miles to go it started to slip/pop out again. Now my scan tool doesn't want to work either.

I bought the car about 2 years ago with 180K on it knowing it had a transmission issue then. I replaced both shift solenoids filter and fluid and not a single issue out of it since until now. The car now has 215K miles and this issue just started.
I've looked all over the web and this forum and the only place I see anything about this issue is a post on this forum in a 10/15/2016 post that mentioned a ECT sensor. "Transman304;812609]The ECT sensor being out of range will inhibit the transmission from going into 4th and Lock up". I'm not able to find anything on the ECT sensor or if that could be the issue. Any help you can give would be greatly apricated.

 

Engine Coolant Temperature sensor, it lives by the thermostat in the same housing, you’ll need a 19 mm deep socket or box end wrench.

https://www.rockauto.com/en/catalog/...+/+sensor,4748

 

Fourth gear is overdrive. It should downshift under some circumstances, like going up hills etc. The computer tries to keep the engines power curve optimal..
Going 55 mph on level ground it is unusual to downshift. Going 40 mph on rolling terrain it will downshift frequently.
Or, do you mean the torque converter clutch disengages, that has its own solenoid. That might throw P0741 or P0742 when it happens, goes away when it stops.
What is the digital coolant temp when this happens? Should be more than 189F.

The likely reason the code reader won't work is the fuse for the front cig lighter is blown. #29 under hood.

 

Thanks for the link, is there one that is better then the rest on this list. Rock auto charges an arm and leg to ship to Alaska. I'll be looking locally for it. I'll swap that out and see what happens. I know I had to do that unit on my 07 2.2 manual to fix the digital temp gage.

Thanks, I'll let you know how it goes.

 

I don't know if it's the OD itself. The problem mostly happens when traveling at highway speeds not necessarily when going up a hill or passlng. I haven't been watching my temp gage to see where it is when it happens but, I will try that when I go get the ECT this morning. I believe it sounds more like the torque converter clutch disengages. I didn't have any codes in it when my reader was working but, I'll have Auto Zone scan for them today. My front fuse is fine and the power outlet works.

I should clarify, it's not the OBD plug that's not working its the OBD reader isn't connecting to my phone. Sorry about the confusion.

 

Change the ECT sensor and go from there.

 

I went for a drive and got the temp up to 174 on the highway at 62mph and @ about 2400RPM and I was running 55mph at 2k rpm and temp of 194. No shift slip out of 4th at all. I was not able to have the car scanned at AZ or OR. I've got home and plugged my scanner into my laptop and got it to communicate with my phone so I'm going to try and plug it back into my car and see if I can get any codes. I just have to wait for my laptop to charge. I have the new sensor and once the car cools a bit I'll swap it out.

 

174? Unless this was within the first 4 minutes or so from a cold start, sounds like you need a new thermostat. ACdelco part number 131-158, accept no substitutes.

 

You need a new t-stat; the temp should get to 180F in about 3 minutes. Never less than 180F while driving. Use real ACDelco 131-158 ONLY
The t-stats job is to keep the coolant temp ABOVE 180F, cheap t-stats tend to get stuck open.
You might not get a P0128 if the ambient temp is in the 70s.

 

Ambient temp is in the low 50's. I was able to check for codes yesterday and there are none found.