where is the ecm?

I believe you are looking for the "Powertrain Control Module".

This is located inside of your air-cleaner housing. (where the air filter is located)

Once you completely remove the air cleaner housing, you'll see it.

Be careful when you disconnect this and install a new one. It's pretty easy to create a shock that will ruin the processor. (electrostatic discharge)

I cannot find the location of the ECM on my 2000 Pontiac Bonneville. I have checked right and left kick plates, under the dash, behind the glove box, behind the ABS computer and other locations. I have followed a large wiring harness under the passenger seat, however, before completely taking apart the interior I would like to know if this is in face where the ecm is located. You guys are great and have some excellent tips and knowledge.
Thank You,

It's in left front of the engine compartment, in the air cleaner housing.

Yea they hide the PCM in air cleaner housing

where is the computer brain box located on a 1997 pontiac bonneville because it wont start sometimes if it has been driven a little bit when its warm i,ve heard the 3.8,s have a history of this?

Hello the PCM or brain box is located at the left front engine compartment. Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Where is the PCM located and what are the color codes for each plug?

there is only one plug as it is OBD1. see picture for location behind right hand side of dash do not forget to take prom out for new ECM.