Will a BCM prevent a car from starting?

Question

I've been dealing with an issue for over a year wherein my 2005 Pontiac Grand Prix starts sometimes and does not start at other times. I had the issue diagnosed last year by the GM dealership.

They told me that I needed to replace the passlock sensor which would cost about $500. I was not ready to get this type of work done at the time, so I recently went back and they recommended that I let them perform a second diagnosis.

This time they returned with two issues. The passlock sensor and body control module needed to be replaced, this would be $1000. Upon asking the service rep, would the passlock sensor replacement solve the "sporadic start issue", she said no. She stated that both parts would prevent the car from starting because they dealt with communication.

Does this sound true? How does a BCM keep a car from not starting?

Additional Note:

• I have not been using my keypad, the battery holder needs repair

Answer 1

In a short answer: Yes, the BCM can prevent a car from starting, and doubly so when you introduce a security/antitheft system like Passlock.

The reason is that the BCM feeds inputs into the Passlock (or other security system) for it to 'determine' if it is being stolen or hotwired. For example: the status of the doors, interior lights, trunk status, etc. and in some cases can even control the fuel pump.

That being said, I would not go hand $1k to the dealership. I would follow this guide and bypass the Passlock system entirely: http://www.bergerweb.net/PasslockFix/

Also note that the guide supports my answer and the GM dealers' association with the BCM in that if you attempt the Passlock bypass and it doesn't work, then you need to replace your BCM.