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Discussion Starter · #1 ·
2006 G6 GTP 3.9

Okay so I am the second owner of this vehicle and have had it going on four years, however last summer after some heavy rain and going through what seemed like "okay" depth of water to drive through, my car has been having intermittent starting issues. I found corrasion in the fuse box under the hood "not crazy but just concerning" and clean out all the relays/fuses with electrical cleaner and a brush, eventually replacing all the fuses/relays, and cleaned the connectors/wiring as well. The car does not stall, made it about 300miles (first started during a trip and had to make it back home) but only will you kill the engine is when the tricky parts kick in.

The first code it threw out resulted in replacing the fuel pump, that of course did not correct the issue and the next issue came from a failing battery/cells, still cranked, drove around for a decent amount of time, no engine light appeared until I would cut off the car the car and/if I attempted to restart the car either from getting gas or going to the store there would be no crank but the lights on the dash would still come on. I noted it seems worst during the day/heat rather than at night due to making a note of the heat coming from the vehicle itself but after inspecting the fusebox's and not seeing anything melted/burnt and letting the vehicle sit for a period of time depending on the heat of the day/night it would eventually start/crank, unless I unplug the battery and let it sit for about 20mins, allowing the memory to reset then the car acts decently for a period of time.​
After the fuel pump I cleaned/checked the ecm connecters and ended up getting "error" on the dash for the very first time which resulted in me trying a new pre programmed ecm but did not take and eventually had to take it into the dealership due to one of the harnesses not making a connection, they were able to get the wiring fixed and I had purchased a new ECM online that required programming at the dealership, for whatever reason the programming would get stuck at 80% and not go forward. Since the original ecm was communicating and the dealership assured me the issue had been resolved after warrantying the new battery due to "failing cells" the car did good for about two weeks and then everything happened again.​

Recently:
The codes relayed to the purge valve/fuel efficiency (broken when the fuel pump was replaced) and code P0420 (catalyst system low efficiency) [newest code to date] and was told to start with the O2 sensors and the purge valve, however issue continued even before displaying the engine light again (will get it checked if I can in the morning).​
after replacing the sensors and purge valve I noted the heater was not kicking in "blower was working" but the A/C was doing fine, now the heater works but the A/C works for a bit then goes hot.​
Reason why I feel it's the ECM/Heat related:
If I make a quick trip down the street the likelihood of me experiencing the issue(s) after having the car sit usually over night I can make it there and back home with no issues, it's only when I drive for a good period of time or go out in the heat of the day, the car does not stall once the engine is going and the thermostat gage on the dash does not go into the red and stays steady in the center.​
during the time of letting the car "sit/cool down" once it acts up I have tried a few things, checking the sensors under the hood, relays, fuses, connections etc. but the only thing that will most defiantly work is unplugging the battery for about 20mins and reconnecting it to reset the ECM gets everything up and going like nothing.​
So I seem to be stuck in a conundrum and the reason why it has gone on so far is because I had surgery back in September an had to put everything on hold until here in March, I am tempted to order another pre programmed ECM (via VIN) and try that one more time now that there is some communication or should I try and see if reflashing the original one would work? I don't see how it could be anything else since the starter & alternator have been checked numerous times along the road now and the relays/fuses were replaced last month too and that it doesn't stall on me while I am driving from A to B no matter the distance and as far as heat I have never seen smoke come from under the hood or seen anything to be melted/exposed so it's all tricky...
 

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Discussion Starter · #2 ·
So got the engine light check today and it again refers to the catalytic converter but doesn't make sense to me since I don't have any issues with stalling once I am going/driving or when I am idle.... odd.
 

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51 Posts
Hi Serg911 - I just saw this... related to your situation?... I have no idea, but perhaps this is something to read.
Goggles.

What is BCM in a Car?

It is common for car owners not to know what their car's BCM is. That can make it quite confusing when your mechanic tells you that your BCM is bad or that the problem is related to your BCM and may need to be replaced.
Your BCM, or Body Control Module, is an electric unit installed in your car designed to handle many of your vehicle’s electric features, including the power windows and central locking.
As you might imagine, the BCM is a relatively important part of your car. It might not always be essential, but your BCM controls a lot of your vehicle’s luxury features that help keep you comfortable. Your BCM may be critical for providing additional alerts and warnings in some cars, like your check engine light or oil lights. Many of the alerts and notifications on your dashboard are directly tied to the BCM.
Your BCM often communicates with other important control modules in your vehicle. That means that, depending on how your BCM is malfunctioning, your car may start to have other problems as well. Strange codes or reduced performance that can’t otherwise be explained may be indicative of a malfunctioning BCM.
Even though it’s one of your vehicle’s lesser-known parts, the BCM is one of the most important electronic components in your vehicle.
What Does Your BCM Do?
The exact responsibilities of the BCM vary quite a bit from car to car. Luxury vehicles generally have more things for the BCM to handle, while cars with fewer features can have a less powerful BCM to manage the smaller number of tasks.
Here’s a basic list of the things your BCM handles. Some vehicles will have more responsibilities than this, and others will have fewer.
Warning Lights
This is probably the most critical function of your BCM, and malfunctioning warning lights can sometimes be an early sign that your BCM is starting to fail. Your BCM doesn’t typically monitor the different parts of your car. Still, it’s a hub that communicates with those other parts and receives information to determine when a warning light is necessary.
The check engine light is one of the most important of these indicators, but other warning indicators like the oil warning are often equally important. If your vehicle provides low tire pressure warnings or tells you when the windshield wiper fluid is running low, those warnings will also run through the BCM.
Less important warnings can often show problems with a BCM along with the more important ones. For instance, your wiper fluid indicator might turn off for no reason without you filling the reservoir, especially if it has turned on and off several times for no reason. Unfortunately, like the check engine light, other more important indicators can have problematic errors that might mean the light is turning on and off for legitimate reasons.
Air Conditioning
Your BCM is also in charge of controlling your air conditioning and is designed to monitor input from your dash, where you set the temperature and the rate of your fans blowing. It then communicates with the air compressor to make sure there is enough cold air available.
Your BCM may also be involved in running your fans when the air conditioning isn't on and stopping the air compressor when you switch over to heat.
Powered Locking System
Your BCM also controls your car’s locking system if it uses an electric lock. If you use a key fob to start your vehicle remotely, the BCM controls that as well. Internal lock buttons are also controlled by the BCM, which is why you can selectively lock and unlock specific doors in most modern vehicles.
Keyless Entry and Remote Trunk Opening
Your BCM also handles distance requests from your fob, like keyless entry where it will unlock your doors as you approach or letting you open your trunk with a button on your car’s fob. The BCM works with keyless detection units and coordinates signals between different systems to ensure your car reacts appropriately.
Basic Electrical Systems
Your BCM also controls some relatively simple quality of life functions that are important for keeping your comfortable and safe while you’re driving. Things like controlling your windshield wipers and adjusting your side mirrors are up to your BCM.
If you’re driving a vehicle with electric seat adjustments, the BCM will control those adjustments as well.

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Symptoms of a Failing BCM
With such a critical part, it’s vital to notice signs of possible failure before your failing BCM can start to impact more critical functions, or even just fail to send an appropriate warning signal when something else goes wrong.
One of the first signs of a failing BCM in luxury vehicles is when the keyless entry system stops working. If your car relies on a fob for keyless entry, it’s essential to make sure the fob’s batteries haven’t run down, but if fob problems have been eliminated, you’ll likely need to look at your BCM as the next culprit.
Other problems, like your windshield wipers not coming on or coming on randomly, can both be signs that your BCM is starting to have problems.
You should also look for other signs that the BCM is starting to have problems, like flickering or random dash alert lights. If your air conditioner starts to have issues and the air conditioning system itself isn’t damaged, it may also be a sign that it’s receiving bad signals from your BCM.
One of the more serious signs of BCM failure is bad or uneven acceleration. If your BCM is sending bad signals or isn't sending correctly timed signals to the other systems in your car, then acceleration is one of the first places you'll see significant performance changes.
There is some good news in all this, though. The BCM is a common enough repair that the part is relatively affordable and easy to get. The BCM is also a reasonably easy part to replace, so many car owners can replace the BCM on their own at home. Mechanics also replace BCMs fairly regularly, so you can usually get a repair without having to spend too much on it. Most BCMs cost a couple of hundred dollars for the part, and labor costs are typically similar.
 

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my first question would be if you’ve checked and cleaned the main ground. But after you said that pulling the battery for 30 seconds resets it, I’d definitely lean towards the ECM or like Goggles said above the BCM. G6’s are famous for having shitty BCM connections. They all get corrosion. Might be worth taking a look and possibly cleaning them up.
 
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