Electrical problems are tough. so many things associated with each other that tend to sway you away from the real culprit. The lights dimming makes me wonder if it's somehow BCM or one of it's connectors related, or the ignition switch. I know I'm going off in a lot of different directions, but this is new and important info. The door, window and seat switches are all on the same circuit coming off the BCM and are controlled through the BCM, and so is the ignition switch

 

Is there a way to test the bcm?

I let it idle for an hour, probing wires for loose connections because that's about all I can do myself is observe. It didn't die but is still having trouble holding a steady idle it seems which has been an issue all along.

From the beginning. Bought the car in August. The previois owner had had a sound system in the trunk because there are signs it was there and removed. The car had been repainted. Was pretty well kept.

Check engine light indicated it needed a new cat. Got that switched. The one on the car before was gutted. The car stalled when backing up a hill but immediately started back. Check engine light came on again p0420. Took it to the mechanic. Same code as before. Cleared the code because the car seemed fine.

The car died while driving at 40 mph, coasting not pressing the gas pedal. Pulled over, lights on the dash stayed on, it just died with no signs of it. It started right back up. Check engine light same p0420 code. Took it to the mechanic he cleared the code because on the computer it read ok.

Drove for four days. Then when parked on a hill and driving down a steep hill about five minutes after it hesitated. Then when coasting again, it just died. Pulled over, to restart but this time it would only stay running if you pressed the accelerator. It died four or five times before I drove it like a scaled dog home. It didn't die gain til we hit our driveway about three miles. Then it started right back and ran fine. Took it to the mechanic. He changed the fuel pump, filter. He checked the relay but he said that had been changed already.

I picked it up, stopped put gas in and drove another three miles and while sitting and idling it just died again. It would not immediately restart would crank but not turn over. I let it sit for a minute and revd it up and it ran fine back to the mechanics. He changed the crank position sensor due to my research and the computer not throwing any codes or reading badly. Then it died on him sitting at idle. He didn't know what to do but take to a dealership which I hate. I notice that turning the wheel drops the rpms and dims lights. The heated seat on passenger side is the only one that works and when you turned it on the dash lights stay dim. When u press the power windows up rpms drop and lights dim.

I took it to auto zone to test the battery. He said it wasn't getting a good connection so he removed the felt corrosion pads. It drove fine all day.

I brought it home, we drove it all day. That night it died on idle. Then it died twice more while driving and coasting not pressing the accelator. Check engine light came back on. Took it to the mechanic. He changed an o2 sensor and found the wire to the alternator wasn't tight and had actually arced and melted. Thought we had found it. The heated seat button no longer dims any lights or changed rpms but still works. The power window button still draws rpms and dims lights. Turning the steering wheel still drops rpms and dims lights. It does seem to take a second when you start for the dash lights and headlights to come on.

Yesterday it drove fine all day til about 3. It jerked a little while driving but I thought perhaps I had tapped the pedal. Then at the stop sign it just died. I put it in neutral and it restarted but as I drove it hesitated, jerked, and rpms would surge then drop with each hesitation. It got better as I drove. If I acceleratored it would hesitate more. I tried to record it but I didn't get it on video. Mechanic drove and felt the hesitation. Thought maybe MAF.

I had ordered an acdelco not reman, MAF earlier so we installed it. I drove it and it's not died but it doesn't del smooth either. Same dimming lights issue and feels like a sputter when driving or idling to me but I am becoming supersensitive to the car now. ...sorry that's so long!!

 

No apology necessary, detail is important.
I think you have more than one problem. Don't think the stalling problem is electrical related. The BCM can be tested with a Tech 2 scan tool, but don't think that's it because once the car is started the BCM doesn't come into play to keep it running. You should get a DTC if the BCM is bad.
I still think you have an issue with the EVAP system, or a dirty throttle body. May have dirty ports where the MAF and/or evap return connects to the throttle body. The throttle position sensor connects there too. How may miles are on the car?
Dimming could be a bad ground.

 

It has 135000 on it. It's not died since installing the maf but we've not driven it alot.
The mechanic cleaned the throtitle body first trip and iac but said it had some carbon deposits.
Also I bought a key fob for it but it will not program to the car.
it has the original wires and coils.
What about the fuel regulator, I am still suspicious of it....Although mechanic said it's ok.

 

Your due for new plug wires and plugs if they weren't replaced at 100,00 miles. Use ACDelco Iridium plugs.

Coils rarely fail and would not cause stalling, but a failing Ignition Control Module could, and overheating can damage the coils.

The fuel pres. reg. was recalled. Quick and cheap to replace, but unlikely the cause of your problem. A pressure regulator failure can cause the Upper Intake Manifold to explode. Saw this happen (Scary).

I would try another fob first, if problem persists it could be the door lock receiver module or Body Control Module (BCM).

Here's a threaded posted by our Administrator "The Maniac" listing recommended 100,000 mile maintenance:
https://montecarloforum.com/forum/fw...0-miles-46078/

I would also add replacement of the problem prone Upper Intake Manifold (UIM) that allows hot EGR gasses to melt through the plastic wall of the recovery port. Use an improved Dorman UIM with metal sleeve to reinforce the port. It comes with a new fuel reg. and PCV. I would also replace the fuel injectors, but that's just me.
"A dimes worth of maintenance is worth a dollars worth of repairs".

 

I will check all those things but I am thinking the intake has already been replaced. I will double check.

The wires and coils are on my list once I get the rest of this paid for. Racked up $1100 plus already on what's been replaced. I am going to drive it today to see if it stalls again and will keep updates posted. Thanks for sharing your knowledge !!!!!

 

Thanks for the updates.

 

sounds like a short

 

So far the MC hasn't died since Thursday. It did act up some yesterday after I put gas in it. I out the nitro shell gas but it didn't die. Today the p0420 code has popped up again. We've been getting this code from the beginning but it has a new cat on it. Could that code be because of a bad fuel cap? I noticed it's not the original cap and the teether is broken off so I had thought about ordering a new acdelco one anyways. Twice it's acted up after putting gas in and the check engine light coming on.

 

Oh and I found a forum about the seat. The burn in the leather seat just above your left butt cheek is sign that the wire has burned. A guy posted how to fix it and all this time I thought it was a cigarette burn!!