2009 Tahoe autostop/nav acting funny
 

Hey folks. I just picked up a 2009 Tahoe Hybrid with 90k on the clock. 4WD, runs very smoothly, though I've noticed two things in specific that seem odd.

First off, the touchscreen / nav works for the most part. When the car starts, and the nav screen turns on, all is well. If I shut the car off and turn it back on, however, the touchscreen is usually blank. The audio still works, and I can listen to radio / play music, but the display is completely blank. The only way that I can 100% solve this problem is by disconnecting the battery for a minute or two, and then hooking it back up. The screen turns back on after that, with a 100% reproduction rate. If I let the car sit for a couple hours or overnight, the nav screen will turn on, albeit less reliably.

Secondly, the hybrid system works great. I get the occasional jitter when switching between autostop and gas-powered, but I can get the car reliably up to 15-20mph provided I'm light on the pedal and on mostly flat ground before it switches over to gasoline. I average about 18-20mpg. After a recent 100 mile trip, however, I came back to the autostop working poorly. It wouldn't come on as often, and when it did, it would only get to about 5mph before kicking over to gas. By the end of the night, it wouldn't go into autostop at all. Last ditch effort, I disconnected the battery for a minute and reconnected it, boom. Autostop works fine again.

Do you think I have a bad 12v battery? Or maybe is there an issue with grounding? I would be inclined to think that this isn't pointing towards a failing 300v, as the autostop works perfectly fine and kicks in at reasonable speeds, and I have no service lights on the vehicle at all. The nav system is the only thing I've had trouble with electrically, and even that works fine after I reset the battery.

I don't want to take it to a dealer but I'm in Los Angeles so I'll probably look for a reputable hybrid shop unless you guys have any ideas. I've read elsewhere that replacing the negative battery cable has helped some people, but figured I'd reach out on here before I do anything. Thanks folks!!!

[EDIT] I fixed the problem by installing a new head unit. The problem was with the nav. It cost me about $560 for a head unit that I was able to drop right in. Read my full response with a link to everything I ordered in the thread below.

Re: 2009 Tahoe autostop/nav acting funny
 

Auto-Stop is effected by lots of things. Engine coolant temperature, transmission temperature, HV battery temperature, how hard or fast you push the gas pedal, and HV battery State of Charge.

A look at the air inlet vent slots near the floor in that back seat and or an inspection of the "Lint Filter" air inlet screen to the HV battery pack may be in order. 100 miles is enough to warm up the battery and get into elevated temperature power limits on EV boogie.

Re: 2009 Tahoe autostop/nav acting funny
 

An 09 with only 90k is a nice find congrats. The people driving the small hybrid cars (penalty boxes) have no idea how awesome these things are. I would probably have the 12V battery under the hood load tested as a first step. In my area almost every auto parts store will happily and free of charge perform a battery test for you. I have an 09 HYHO with the original hybrid battery that has over 200k on it. I currently use it as my daily driver. Love the vehicle the gas engine and electric drive combined are right at 400HP it is a monster! Mine has a 3.5 lift and 10x20 wheels with Nitto Grapplers and still gets 17 mpg. I could easily crush up some "penalty boxes" if I wanted to LOL
Hillbilly is spot on about cleaning the battery inlet screen and checking the air inlet slots at the base of the seat to make sure you have clear airflow, that would be my second step after the 12V battery check.
https://cimg5.ibsrv.net/gimg/www.gre...64b55608bf.jpg

Re: 2009 Tahoe autostop/nav acting funny
 

Hey thanks for the good word. I fixed the problem. It was a bad negative battery cable. As I slowly started to narrow down what was going on, I also found out that the cruise control would only work when the navigation wasn't working, and vice-versa. I did a 6 hour drive up to the mountains and the Nav just randomly turned on about halfway through, right as that happened the cruise went off.

I read that replacing the negative battery cable is a good first step to attempt solving any electrical gremlins. Once I threw the new cable on, boom, nav starts up every time, cruise control is working as it should. Unscrewing the ground cable from the bottom of the truck was a MASSIVE pain in the ***. The whole repair took me probably about three hours. I'm not very mechanically savvy but I wasn't going to take this to the dealer for $400 if I could do it in my driveway for the price of the cable.

The only thing that I could foresee having any issues moving forward is that I used a battery cable for all non-hybrid GM vehicles rather than the Hybrid specific cable. I ended up needing to extend the battery post a couple inches with an adapter that was $8 at Advance Auto.

Re: 2009 Tahoe autostop/nav acting funny
 

Update. After about a day and a half of the nav working with no problems, I turned my car on midday to find that it's not working anymore. Back to square one. I'm going to put the adapter on the battery to get a more permanent solution with the negative brake cable but other than that I'm not sure what my next move is. Test with a new battery?

Re: 2009 Tahoe autostop/nav acting funny
 

Key seems to be that other things other than Nav are going out. Lets get a cig lighter power monitor plugged up and see if it the battery power is indeed dropping off when the problem occurs. There are many different ones out there that you can buy here is one that popped up when i checked.

Re: 2009 Tahoe autostop/nav acting funny
 

Good knowledge. I'm going to go get the battery tested tomorrow, Autozone does it for free so if it's the battery maybe throwing a new one in will replace it.

I replaced the brake light switch today, took me 5 minutes, and the cruise control SEEMS to be working, and it engaged while the navigation was working. But again, these electrical things are so on and off only time will tell. Will keep updating the thread as I go through my repairs.

While I've got you here - would you happen to know what your oil pressure hangs around? When I cold start, I'm at about 60, and when the engine has run for awhile, it will stay between 20-40. Sometimes on idle it's just above the 20 mark. Driving it's around 30-40ish. Seem ok to you?

Re: 2009 Tahoe autostop/nav acting funny
 

Hot Idle oil pressure should stay 25 or above however I am not sure how accurate the dash gauge is? Mine shows around 65 on cold start then runs around 40 at idle after fully warmed up. At speed where the rpms are up on the road it will run 45 to 50 typically. There is a screen underneath the pressure sensor at the back of the engine that can get partially blocked (if the previous owner did not do timely oil changes). I would probably pull that screen and replace it if I suspected a pressure problem just to make sure that this simple item is not causing a bad reading. Biggest concern is that IF that screen does becomes completely blocked the upper AFM VLOM components will be oil starved and destroyed so any oil pressure discrepancy would lead me to that specific part as a first step mainly because it is easy and simple. These GM engines are also known for seal leaks here is a link on the camshaft thrust plate issue and a way to test for that issue. https://roadmasterengineworld.com/20...-6-0l-engines/
That is a bit more involved fix. There are also issues with the oil pickup tube oil ring in the oil pan another more involved fix. Have you changed oil and filter just to make sure it has the proper 5W30 in it?
my 2018 GM 6,2 uses a super thin 0W20 oil it looks and is incredibly thin oil but works great in the engine that it is designed for. I could see that causing an issue if was to be run in my 09 Tahoe 6.0 .......
https://cimg0.ibsrv.net/gimg/www.gre...7dcb9d81b6.jpg
https://cimg1.ibsrv.net/gimg/www.gre...3287498698.jpg

Re: 2009 Tahoe autostop/nav acting funny
 

Thanks for the pictures and general contribution to the public knowledge. I'm sure there's many out there in earlier stages than you, or even me that will find this stuff super useful. My oil pump is definitely working, although it seems to be a bit lower than yours so I'll get that screen checked. The sending switch above the screen got replaced recently and it only took about 5 minutes at the mechanic so I'm going to try to find the screen myself. If you have any advice as to what I can use to pull the screen out would be much appreciated, otherwise I'll just poke around my garage for something suitable. I bet it's blocked in some capacity. The vehicle doesn't burn oil any quicker than a regular vehicle so I would be inclined to believe it's not a leak.

I'm also considering deleting the AFM with that OBD2 plugin - thoughts on that? I'm just thinking about longevity, the higher MPGs is nice (600 mile trip last week averaged close to 20) but if it means i'm putting more wear and tear on the engine then an AFM delete sounds like the right call.

Re: 2009 Tahoe autostop/nav acting funny
 

I use the OBD2 AFM delete and it works great! I also use Motorkote with every oil change.