Major power loss! Engine code P1639

Hello, I'm new to this forum. Needing some help narrowing this down. I have a 03' Regal, 3800 engine, auto trans, about 143,000 miles with an engine code of P1639(5 volt reference 2 circuit). Started about a week ago when the check engine light came on. At that time the car still ran fairly good. After a few days I started noticing a loose of power during acceleration and pulling hills, along with some weird shifting. Today, it really declined. Major power loose at about 2000 rpm's and it really didn't want to go any higher unless I really pressed the pedal down far, then the whole car seemed to shake. Didn't seem like it would accelerate on the highway. Lost speed going up hills. The trans seemed to be shifting harder. While parked the engine starts coughing at 4000rpms. :shakehead I was told it may be the converter or the Fuel Tank Pressure Sensor causing voltage drop. Thanks for any input or advice. I'm a pre-computer guy when it comes to engines, so i'm a little ignorant with this type of thing.

What elements to you need for a good fire?
Air, fuel, ignition, and exhaust.
1) Check catalytic converter for being plugged.
2) New air filter, clean MAF sensor
3) Clean throttle body
4) New fuel filter + check fuel pressure.

Isn't the P1639, causing an air condition problem.

Caution - A plugged catalytic converter will cause engine damage, have it checked free at any local muffler shop.

P1639 - PCM 5 Volt Reference signal low or high

Sounds like either a broken wire or a corroded connector at the PCM.

I had the same symptons on my 2001 Buick Regal (105,000 miles). Loss of power and hesitation when briskly accelerating. Car idled fine. I could feather the accelerator to get up to speed without the problem occuring. Took the car to the dealer today and they diagnosed the catalytic converter. Will cost $325 for a new converter (after market) including labor.

I just had the same situation with my 2001 Regal, replaced the cat, resolved the issue.

See notice at link below which has been posted at our Buick Tips & Maintenance for several years now.

It looks like jjdublin was ripped off by the stealership since with his mileage and year CAT converter replacement should have been free or covered. Also, I received notice direct from GM when I still owned my 2001 Regal GS but now sold.

Click here (http://www.automotiveforums.com/vbulletin/showthread.php?t=681281)