[mdoyle]

If you have an auto parts store near by they might have a code reader to loan at no charge. There is an OBD-II port under the dash near the steering column, you plug a reader into that and it will output either a code you look up in a book or the device name depending on the reader.

When it's emissions related the 02 sensor is a common suspect. I've also noticed that extremely cold weather tends to throw off the emission control equipment on my H2 which coincidently is an 03 with about the same mileage as yours.

I suspect when it's uber cold the MAF isn't doing it's job and the mix ratio is a little off which causes the O2 sensor to error out but that's just a guess.