Where is PCM location 2003 GMC Sonoma 2.2 Outside of engine compartment underneath cooling overflow bottle?

hi john.
not sure if you will find out from this link but have a look.
What is the fuel pump pressure on 2003 gmc Sonoma 2 2 sfi truck Google...

Loosen the lower radiator hose, most engine cooling systems hold about 2 Gallons or more. Just precaution have at least a 3 gallon catch pan/bucket that will fit underneath the van.

Powertrain Control Module (PCM)
On the right side of the engine compartment

First thing to check would be coolant level in return bottle and/or rad. If you have a rad cap, remove it, start engine, turn heater on and add as necessary when engine at operating temperature as needed. Wait until you see increased flow through radiator before topping up and putting rad cap back on. It may be that coolant level is just low enough to cause airlock in heater core.

The PCM for what ?
There are several PCM ( part controle modules) in any given vehicle... Most are integrated in the ECU .

PCM-Behind Glove Box,inside car,you can see and feel it.
-connectors are outside in engine compartment,under Cabin Filter Housing

There is a raidator cap that can be unscrewed when the engine is cold fill this to the top then there will be an overflow bottle and it will say engine coolant on the cap, fill this to the full mark and you should be on your way :)

With engine cold, remove radiator cap. At bottom of radiator on left side (as you stand in fronof truck), there is a plastic drain plug that screws into the radiator. This plug does not look like a bottle cap, rather it looks like a large, raised tab. Turn counterclockwise to remove. Have a large pan under the truck at this location, or have the truck parked on the grass. Allow to drain completely. Dispose of the old antifreeze and do let children or pets drink it; it is deadly poison. If you want to do this right, replace the plug, refill the radiator with water only, replace the radiator cap, start engine and let run until opwerating temperature is reached (about 20 minutes), then turn engine off, let cool completely, and repeat the drain procedure. This will more thoroughly remove the old antifreeze from the system. Now refill the radiator with the proper mixture of new antifreeze and water, run engine to proper operating temperature. turn off engine and let cool completely. Add additional water and antifreeze into the coolant overflow bottle if necessary. After changing antifreeze, you may need to add more again after couple of days.

2 the right of dist. cap

The sensor is located in the lower part of engine block, it goes into the water jacket of the block, so dreain the system before you remove it, get a new one before you look for it so you know what you are looking at while under the truck.