With the lights acting goofy, my guess would be the BCM.

I had a no-start Passlock issue with mine. The guy that changed out my ignition, went through the glove compatment and then took off most of my dash getting to it. Glad we didn't try to attempt it.

 

The code says that your theft deternant enable signal lost. Here is a informational link on how it works. I would research it for awhile and I bet if you call the Chevy house they will give you some info on how to reset the system.

http://www.hotrodlane.cc/New%20LT%20...nal%20Lost.htm

 

Had to replace the BODY CONTROL MODULE found DTC P1626 that can cause a no-start condition or normal operation depending on when the loss of the fuel enable signal was detected only got a CHECK ENGINE LIGHT nothing else wouldn't start or crank over. Had to take it to a Chevy Dealer to have it replaced and reprogrammed that corrected the no start condition. I'm providing this information in case some one else may have the same or run into similar problem.

 

How much did this end up costing you?

 

Weird, haven't heard of that before. I was also starting to think it was the infamous passlock issue.

 

Yes it looked like and is related to the no theft issue but it turns out the car wouldn't start and only the check engine light came on and the car was basically locked out and wouldn't start never seen this problem like this. Replaced the BCM corrected the problem since it controls everything any way did get the instrument panel lights cycling off and on also which was another clue the BCM was bad.

 

I had a bad BCM replaced last week.

Symptoms:
WHILE RUNNING:
Security Light on message center
Battery Light on message center
Service Vehicle Soon on message center
Volt gauge going from far left to far right
Radio says, "Locked"
Rear view mirror lights always on

NOTE: These symptoms did not always happen at the same time. Each time I started the car, one or more of these would happen.

NOT RUNNING:
No power to gauge cluster
Radio says, "Locked"
Relay click when trying to start but no turnover


When the car would not start, I could disconnect the battery to "reset" the symptoms and crank the car but it would come back pretty quickly once the car was started. It did stay running though.

When I took it to the dealer, their scanner tool could not communicate with the car until they removed the BCM. He said it was disabling the BUS somehow.

COST:
Parts (BCM) - $236.67
Shop Supply - $26.53
Labor - $294.00
Total: $559.13 + tax

MY THOUGHTS:
The service guy attempted to get me to authorize a "Wire Trace" as they could not figure out the problem because the scanner tool could not communicate with the cars computer. I stated that before I would authorize that, I wanted them to check the BCM first. He came back 10 minutes later and said it was the BCM. I think its ridiculous that a vehicle REQUIRES you to go to the dealership to get it fixed and then they aren't even aware of common issues with it.

 

My 01 Monte Carlo LS just had the same exact problem but I had a double whammy. Both the passlock and then the BCM went bad and cost me $736.00 to repair. I'm glad they both have a 1 year warranty on them since it was done at the dealer.

 

Same basic problem I sometimes get-

No lights, including dome
No cranking
No accesory power

Only a check engine light

Battery connections good
Batt voltage good
No corrosion

Reconnected the terminals and it ran perfectly

Just a week ago i dumped 1000 dollars into fixing the Passlock problem and keying the new cylender at the dealer, and here i was stranded by my Monte again.

 

I had same problem and dealership said BCM wasn't sending signal. So 549.00 later had it replaced and reprogrammed, DID NOT fix the dash light going on and off problem but seemed to help starting problem, or so I thought,,3 days later the starting issues are back, first it was every 3 or 4 days now everyday at least 1 time we don't start, sometime I can put it neutral and it'll start right up but lastnight it NOTHING helped and this morning I go out and viola,, starts right up.. ANY suggestions out there..I LOVE MY MOTE CARLO but am tempted to "CURB" it if I can't get help..