G'day all.

2008 Hummer H3 owner in Western Australia with a tricky one that I can't seem to find an answer for and I'm hoping someone on here might have a better idea. I apologise in advance as this is a bit of a novel.

To quickly sum up, my car would completely shut down on hot days when at very low speeds or stopped and wouldn't restart until the engine bay cooled down. I would get P0601 error code when diagnosed, and the dash would flick through STAB SYS - TRACTION - FAILED - REDUCED - POWER - SERVICE with the check engine light on also. When the car would shut down it would just straight up stop dead. No sputtering, changes in RPM or anything. Just completely shut down as if I had switched it off with the key. When the car would restart, only the check engine light would be on, the messages on the dash had gone and the car would run as if nothing had happened. I had the car serviced, oil, coolant and battery replaced and topped up with premium fuel and the issue still happened.

Now onto the story...

In our summer last year we were experiencing a particularly hot one. On the days I was experiencing this issue, the average temperature was around 38c - 40c (100F - 104F)

First time this happened, I was sitting in a carpark with the car running and aircon on. I had been sitting on the phone for about 30 minutes when the engine shut down with the above error codes. Thought it was odd, but I went into the shops, came back and started the car no problems with the check engine light on.

I thought this was weird so I immediately called up the mechanic who changed the oil, coolant and replaced the battery. Figured I'd pick the low hanging fruit for the problems first.

The car ran fine after this until the next hot day. Had been driving around for maybe an hour. I parked in the carpark, went inside for about 20 minutes, then came back out to the car, started up and drove off. After a minute or two and still trying to get out of the car park the car shut down while going maybe 5-10km/h (3-6 mph). The engine temperature was only a touch over the midpoint on the gauge and there was no indication, lights or warning messages to say this was an engine temperature problem, only the above error messages on the dash. I waited until the ambient engine temperature cooled and the car started no problems.

I ran the gauntlet and drove home. The issue happened 3 more times. Each time it was when the vehicle was driving slowly, stopped, or accelerating after being stopped. Once while going slowly around a round-about, the next time while stopped at an intersection waiting to cross, and finally when crossing another intersection after being stopped. Safe to say this wasn't very fun. Each time the same error codes, and the same way for starting (pop the hood and wait for a couple of minutes).

I called the mechanic back out and was able to cause the problem twice more while he was there, but he was totally stumped as to what the problem may be, saying he thought the problem was with the PCM but it was out of his field of expertise.

I pulled the PCM apart to see if there was anything obvious, but it all looked totally fine.

A few months on and the temperature has cooled, the problem hasn't happened again and I've been driving around for 5 months. My theory is that in the high temperatures, something is expanding, causing an error and making the car shut down. I'm more convinced of this because the problem never occurred when while I was driving around at normal speeds when the engine was working harder, but would always occur when the car was sitting still or cruising very slowly and not getting much airflow over the engine bay.

Just thought I'd try on here to see if anyone had experienced the same thing. Hummer is not very common in Australia and it's hard to find anyone locally who is keen to diagnose.

I'm hesitant about taking it to an auto electrician or another mechanic and spending hundreds of dollars for them to fault find and not get an answer, as I've seen in a few forums people seem to go down rabbit holes with no real results.

I was thinking to potentially swap out the PCM? But unsure whether this is the correct answer either.

Again, I apologise for the novel I have written, just thought I'd try write up a full appraisal to give everyone a clear picture.

Thanks for any help!



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was the battery voltage low when you got the P0601?
P0601 is a PCM issue with the read only memory circuit inside the pcm. a low battery can cause bad data in the rom.
as can noisy power that has spikes in the voltage from bad diode's in the alternator

 

When testing any circuit for open or continuity/ resistance, it is imperative that all related terminal pin fit and tension be checked when the test steps require disconnection of the connector or component, prior to any component replacement.

 

When the fault first happened the battery voltage would have been low. After it happened the first time the mechanic swapped out the battery with a brand new, fully charged one. However it still happened another 3-4 times with the new battery and only on really hot days.

 

Are you still trying to use the Crappy Azzed OEM Battery Terminal Connectors???????????? If so, hack them off and replace with a quality aftermarket set like Stingers or your favorite brand.

The FIRST mod to be done to every H3/H3T.

 

I'm gonna go way out on a limb here, lol and ask the basics.

Have you changed the water pump?
Have you changed the Fan Clutch?
Have you cleaned the Rad interior/exterior?
Have you at least verified that the two main grounding lugs are good and clean?
They are located by the ABS/EBCM modul and behind the Air cleaner box/filter assembly on passenger side... Take them off and clean the ground point and soak them in DEOxit or the like. Even vinegar and baking soda work.
Have you verified that your OEM battery cables are clean, tight and functioning as designed? (they suck :')

The next step will be to look at live data while the error is reproducing itself.
But I'm kind of thinking the basics should be done first. If nothing else then to rule that out.
With that kind of idling and slow movement it leads me to think that the under hood temps are as you stated " something is expanding " The TCM could definitely have something to do with it.

 

I didn't know about this! I'll be sure to swap it out though. I am very new to having a crack at fixing stuff up, and definitely want to start doing some upgrades. Thanks for the advice

 

Definitely not going out on a limb! I am very new to fixing up my Hummer and will definitely take all the advice I can get. I know my way around tools, and there's plenty of YouTube videos to help me out. To answer your questions, I haven't attempted any of those things.

I will certainly have a look at the grounding lugs. I do believe there is some sort of an earth problem happening with some other small ****ling issues.

My main issue that I face is forcing the error to happen again. It's winter here at the moment and temperatures are much cooler. I have been driving the car every day, sometimes for extended periods, and the shutdown hasn't happened again since. My initial suspicion was high temperatures being the culprit, and this just seems to confirm it.

I had a quick read on the TCM function. Would you expect that I would see fluctuations with RPM, or the car behaving weirdly before the error occured if the TCM was the issue? There is absolutely no warning before the car shuts down. Runs smooth and clean. It is quite simply as if the key is switched off and the car turns off. It's as if the car is in a protected mode until it cools down, as there is no response at all if I try to start the car immediately after while it's still hot.

It's a head scratcher for sure, but I will certainly try doing some of the basics first to eliminate some easier problems. Cheers!