Hi all! Hope y’all are staying safe and on the road with yalls hummers!

I really have been in love with my hummer H3, but recently it had an array of problems. Anyways, the engine now cuts off at random. I could crank the car and drive 500 miles, or I could drive it to the grocery store, only to have it shut down in the parking lot on the way out.

Steps I have taken:

I replaced the battery terminals with new “Top of the Line” Connectors.

I replaced the battery.

I tested after unsuccessfully start waiting 10 minutes- no fix. Sometimes it starts fine after 5. Leaving me to believe nothing to do with passlock.

Im left with no cheap fixes, and would like some opinions.

The problem in deeper explanation: Car starts fine after no use, overnight or 4-5 hours after last use. Drives absolutely perfectly until you get where you are going. Once you try to restart your car, it’s a 50/50. Sometimes the car will get you another 50 miles, sometimes it will break down leaving the parking lot, leaving you struggling to get 5 miles in 2 hours. All the inside components stay on- stereo, Ac, etc. Also, the car does not honk when it is locked and the headlights occasionally flicker. (Both, not just one).

Again, I don’t think it’s passlock, on multiple different occasions, I’ve removed the key from the ignition, waited 10 minutes and some change, and tried again to no avail. Also, I’ve tried the slow start method.

What I believe to be the problem: I do not think it’s the fuel pump, as the car drives fine sometimes, and won’t others.

The passenger floor board was absolutely soaked, I had the car work on and it was neglected. Over the course of a particularly rainy month, it was stored outside. I got the car back with an extremely wet floorboard. Could it be the notorious bcm?

I also believe it could be the ICM.

I know very little about cars, hoping someone can help. Thanks.

 

Get to BCM, take it off, open case, inspect for water damage, inspect connectors.
Get scanner, scan for errors.
Check fuse box, pull off some fuses/relays, check for oxidation damage.
Check for trailer connectors, are cables not damaged, oxidation damage again.
Easy small steps.

 

Thanks for the reply. I’ll try that later. Would you recommend getting into an AutoZone parking lot before doing that? I still use my car to travel frequently.

 

Sorry, I don't understand that last question, I am not from US.
As I understand AutoZone is parts shop and you want to make sure you can have extra on hand if you break something or find something broken?
I have no idea if Autozone stocks Hummer specific parts, but relays/fuses/electric cleaners, probably.

I keep my truck in garage and do all maintenance there and order everything from US and it takes weeks to get here

 

#1 Fix your sunroof issue that caused the possible water damage to the BCM. Plenty of info on plugged sun roof drains and how to mod fix those here, do a search.
#2 Plan on replacing the BCM after you try to do what LatvjuAvs recommended.... you might get lucky and just need to clean contacts, but I doubt it.


I know what a PCM is, got no idea why you would think it could be the ICM???? ICM stands for Ice Cream Man, so unless you pizzed him off or he has some vendetta against you, I would doubt it.

 

At least it wasn’t an ICBM he pizzed off , that would have devastating results.

 

I appreciate the continued support! I will update you! Thank you so so much!

 

I shorted him and then stole his wife with my rolling hunk of sexy metal. Us hummer owners know the deal!

 

Hey All. I did some more research and some more thinking

Does anybody think that a bad ECM could be the problem?

Like I said, intermittent problems, otherwise drives fine. Stalls out and won’t run steady for a few hours other times. No Engine Lights of any Sorts.

Also: Can anyone link me to a BCM guide, like any information on how to access or assess it?

Big thanks to everyone! Y’all are saving me hundreds if not thousands!!!!!!

Stan

 

You likely have a water damaged BCM, you reported the passenger floor was soaked. The BCM is located behind the passenger side kick panel, pop that off and there it is #1 below.




Plugged sunroof drains cause water to run down the A Pillar, behind the dash and..... what is below that???? the BCM. When they get wet, they can completely short, get corroded, have intermittent voltage readings, or have all kinds of crazy symptoms like you describe and a bunch more. Lights flicker, radio stays on or illuminated, dash lights are lit that may or may not be in use, wipers can start and stop, tail lights either do not work or stay on all the time, dome lights freak out, turn signals won't work or come on and off by themselves, and a 1000 other things like shutting off the engine because it thinks the vehicle has the key turned to off or there is no key in the ignition. The BCM is connected to the passlock system and monitors the ignition switch position and status.

If you are lucky, it may just be a passlock issue caused by a bad ignition switch.

The PCM is located under the hood against the firewall behind the windshield washer reservoir and therefore it cannot get wet from rain with the hood shut. If it drives at all, that works.