05 tahoe, loose all power for a split second

[mkatts]

I am cruising down the interstate at 70 mph. The engine cuts out for a split second, the doors unlock and lock, the gauges drop and come back. Basicly lost the electrical syste, for a split second. But it happened over and over on the way home. The thing is, once I dropped down to about 50 mph, it was fine. I went up to 70 and it started doing it again. WTF?
Got home and checked battery connects. They were tight. I have been having problems keeping the + cable tight though. Took them off and the they were clean. Looking more closely at the + battery terminal, It is gouged out pretty good from coming loose. I put a wrench on it anyway and got about a half a turn out of it. Took it back out on the highway and it was fine. I think I am going to replace the battery and possibly the + cable. The + cable goes down close the block and splits off up to the alternator. It also splits off at the battery term and goes under the fuse block. I couldn't get under the fuse block without major surgery, but the split down by the block is closed in a small red junction box. The connects in there were clean and tight. I need to get it up on stands to check the connects at the starter and the ground. Odd that it's fine around town but when I get on the interstate up to 70 it freaks out.
This will be fun to fix. :eek2:

 

[Rivieraracing]

Did you ever get her figured out?

 

[mkatts]

No. Replaced the batter and the terminal bolts on Sunday thinking that since the pos cable kept comgin loose that was the problem. No dice.
I did notice that I am not loosing the radio or compass when it happens. The SES light comes on, the tach drops a few lines as does the the spedometer. Plus the doors unlock.
Now I am thinking it's the ECM. Since the ECM locks the doors when shifted into drive, and unlocks when shifted into park.
So I am really leaning towards the ECM.
Thoughts?

 

[Rivieraracing]

Just a stab in the dark but do you have any kind of aftermarket alarm or remote start installed in you truck? When you are hitting 70, is your tranny downshifting at all at that time (since you are still having that problem as well)? Keep testing her out and keep trying to notice what else is staying powered up when everything else seems to be losing power, that can really help figure out the problem. It could very well be computer related, just hard to tell right now, are you getting any codes popping up?

 

[mkatts]

No after market alarm or remote start (I am going to install one this summer)
Yesterday it start acting up when I went to pass someone, but I don't think I stepped on the gas enough to kick it down a gear. I will have to try pay attention to that today on the way home. Neither the radio nor the heater blower shut off when the engine cuts out. So it seems more like the ECM the more I think about it. I think the loose battery cable was just another problem. Or it could be what messed up the ECM to begin with. When I first found the loose cable it was hanging on by a thread, literaly.
Where is the ECM located in the 05 Tahoe? It's been forever since I replaced one, then it was on the passenger side kick panel.

 

[robj]

if the SES light comes on that means it threw a code... go get the code read and you will have your problem : )it will be in the history you prolly need a gm Tech II to find it

 

[JKmotorsports]

Now I am thinking it's the ECM. Since the ECM locks the doors when shifted into drive, and unlocks when shifted into park.
So I am really leaning towards the ECM.
Thoughts?

BCM (body control module) controls those functions, but you mentioned the ses coming on. As far as I know, only the PCM (powertrain control module) can throw the ses light.
The bcm is underneath the driver's knee bolster and the pcm is in the engine bay towards the front on the driver's side.

 

[mkatts]

The SES light come on during the split second that the engine stalls and goes back off as when the engine picks back up.
The PCMm is under the Fuse block then on the drivers side?

 

[JKmotorsports]

The SES light come on during the split second that the engine stalls and goes back off as when the engine picks back up.
The PCMm is under the Fuse block then on the drivers side?

Closer towards the front, in a black cover. There will two harnesses plugged into it.

 

[mkatts]

It's pouring down rain otherwise I would go look, but on my truck, I have the battery, then right behind that is fuse block. Going off of memory, there was a large amount of wires going under the block, but I figured that was because of the fuses. I will hopefully be able to check it tomorrow. What is the estimated cost of the PCM?

 

[mkatts]

Decided to just replace the PCM. CAlled around, it's a dealer item only.
Called the dealer, WOW!:wow: $568 plus it has to be programmed by a GM shop! Part guy suggested getting it diagnosed first for $75 before dropping over $600 when you include install/programming.
So I decided instead to subscribe to onstar for $20 and see if they can run a diag on it first. The onstar guy said it takes 24-48 hours before they can do diagnostics.

So I'll give it a try in a couple of days.

 

[01smellytahoe]

Don't subscribe to onstar!!! just for this. Their codes are generic and will basically tell you you have an electrical problem. Get it checked at the dealer. It may not have even stored a code. You have a power loss, think about when you just turn the key on without starting the ses light comes on then too. If it's powering all the way down quick enough the light just may pop on. I'm leaning toward fuse block problem. I don't go back to work until monday and then I can ask the techs. Right now I'm gonna check dealerworld for any bulletins. Ok, no bulletins.I would also recommend going to autozone and have them check the codes. See what you got and let me know.

 

[01smellytahoe]

I remember seeing this same thing and the fuse box had to be replaced, almost the same complaint.

 

[mkatts]

well hell, to late!
i already subscribed! Haven't called them yet though. Was going to get it out on the highway make it screw up while they are on the line.
I appreciate you asking the techs there too, that'd be cool.
Do you remember what in the fuse block was messing up?
I agree that the SES light is just coming up because the engine is stalling for a split second. I didn't think it was throwing a code because it does not ever stay on like a code has been set. I was also under the impression that all Autozone can do it just pull the codes out. Do they have the abilty on these newer models to look at the specs in the computer?
Thanks again!

 

[01smellytahoe]

autozone will just give you codes, sometimes a little more than onstar. I believe it was a ground problem, don't quote me though. It's been awhile.

 

[mkatts]

Your were right, Onstar was clueless. It was cutting out while he was looking at the computer and he said everything looked fine. On the plus side though, the Onstart system did not cut out. I had my wife with me and she verified the the neither the radio nor the heater cutout when it died. It really seems like someone is turning off the engine but not turning the key all the way off.
Not sure why the doors would unlock though. Under normal conditions the doors unlock when I shift into park.
Going to reluctantly call the dealer tomorrow and set up an appt.

 

[Rivieraracing]

It would probably be a good idea to make an appointment (I hate it when I have to say that) with the stealership, at least your problem is consistant and they should be able to figure it out because it is, hope it doesn't cost a ton though!!! Good luck with it and let us know about their findings, and while you are there mention your tranny questions and see what they think, small chance they could be related or at least give you their opinions of how normal they think it is.:thumbsup:

 

[mkatts]

Took it to the dealer today. They said the transmission was about out of fluid and that a transmission service would fix it. I asked where the fluid went since there are no leaks. He said he has seen where the transmission can get an air pocket and the fluid gets burned up. I have never heard of this. I know the fluid is burned, i looked at it when I looked it over. I did not check the transmission fluid after driving it. (shame on me). I told him to go ahead and do the trans service since I know it does need it. This could explain the the wierd shifting pattern as well. If this fixes it, I am going to be pretty embarrased.

 

[mkatts]

Well the problem is gone. Talked to the mechanic. He said it wasn't out of fluid, just a quart and half low and extremely burnt. Said the pan is pretty shallow so a quart is a lot of fluid. Part of me wants to believe that they fixed something simple and then dinged me for a tranny service. Oh well, it cost me $160 to get it fixed. Im a little embarrassed that I didn't check the fluid level more closely. I pulled the stick when I first looked at it, just to note the fluid color. It was dark but it was on the stick. Since the trans was cold, i didn't bother looking at the level. Was going to when I got back from the test drive but forgot. Then after I bought it and this cutting out thing popped up and didn't even think about the transmission. Never would have made the connection between the engine stalling and low trans fluid.
Oh well, what are you gonna do?

 

[mkatts]

Nope, problem still there. Called the dealer back. Said tech never took it out on the highway to test even though the work order specificly says, engine cuts out at highway speeds only.
Spoke to soon. :cryin:

Updated:
Taking it back today to let it sit overnight so it's nice and cold for them in the morning. It seems like it smooths out when it's warmed up. Also noticed today that when it starts messing up, the cruise control no longer works. This has to be the PCM that is the problem