My check engine light came on about a month ago so I ordered Actron CP9125 PocketScan Diagnostic Code Reader for OBDII (Post-1996) Vehicles off amazon. I selected free super savor shipping and they used DHL who gave a delivery date of over 3 weeks out. A few days ago after some hassling I got refunded as they shipped it to the wrong address. Before I repurchase the scantool I was wondering if anyone had used it before or had any advise for fairly low priced scantools with more features.

The main reason I am posting is that I am sick of waiting to fix the car. Over the last 2 tanks of gas i have avaraged 12.7 mpg. I am pretty sure it is the O2 sensor from reading on the forums and that being one of the main things I should have done on the last tuneup and could not afford to. Should i be fairly sure that it is the O2 sensor and just go ahead and order the new ones so i can replace them?
If i do replace them should i replace both? Thanks for any advise anyone can throw out there.

Some of the auto parts chain stores will check codes for you. You could have any number of problems that could throw a code. You could just have old plugs and wires causing lower gas mileage....

The O2 sensor has to be pretty well dead before it will set a code. As fbody69 suggested, get the code pulled at Advance or Autozone, as a start. If your car has over 50k miles, it would be about time to replace the O2 sensor as it is likely getting tired. The front sensor is the only one that will affect your gas mileage. If you replace it, get only an AC/Delco, or Denso sensor. The others have been shown not to last very long.

As he also mentioned, a good tune up will help also, if you're due. While you're doing things, a throttle body, and MAF cleaning would be a good idea. "How to" is in techinfo.

I have an AutoEnginuity scan tool that I picked up off from Ebay. It attaches to my laptop, and there are Palm versions. Some like the Auto Xray self contained unit, and many run the Aeroforce gauge installed in the car.

Just got back from Schucks where they let me use their scantool, the code was PO128 the scanner said Coolant Thermostat (coolant temp below thermostat regulating temperature. I checked the coolant and it appeared to be the dexcool coolant that I've read causes a problem with the LIM gasget. It was about 1 inch below the hot line and the engine was warmed up to around 190. I was planning to do the LIM fix from the techinfo article over the summer along with probably cleaning the throttle body (will the guide in techinfo for the previous generation bonne be the same as mine?) and putting in Intense L36 level one performance kit.
I would appreciate any advise available on what this code probably means the problem is and how to fix it, Any ideas of how to fix my low mpg (I used to get around 26mpg or better on long trips).
Also is it probable that the coolant loss (if 1 inch is significant) is tied to the LIM gasget problem and if so how critical is it that i fix it right now instead of this summer. I drive my car around 15 miles a day with 1 or 2 600 mile trips before summer.

This is a common code when you swap out your thermostat to a lower one ie 180*f stat.

It basicly means the pcm was expecting the engine to be up to a certain temp in a certain amount of time and it wasnt so it thru the code. I have seen it many times myself.

In your case it could be your thermostat is stuck open or its really cold outside.
Either way a cold engine does burn more fuel so I belive your on the right path.

Over what period of time did you have that coolant loss? An inch can be significant, especially over a short time. Any sign of moisture, or light brown gunk under the oil filler cap? If so, you will want to move the UIM and LIM repair up a bit.

Do you have a stock 195* thermostat, or did you put in a drilled 180*. If stock, the thermostat is likely defective. That code comes up when the engine doesn't reach operating temperature quickly enough. If the drilled 180* and you live in a colder climate, you may want to consider swapping it out for the stock one during the colder months. The engine running too cold will affect your gas mileage.

Edit - Beat out by "quick fingers" PDad.

The check engine light came on when it was around 0-5ish degrees F out driving through 2-8 inches of slushy snow all over town so I think that would definetly cuase the engine to heat up abnormaly slowly. Earlier I checked the dipstick for any milky bubbly or brownish fluid but didnt think to check the inside of the cap. The dipstick oil looked normal if a bit in need of a change. I'll check the cap when I go outside in a bit. I cleared the code this morning and it hasn't turned back on (its around 45 out today and snow is gone).
As far as the coolant I checked it when I bought the car back in Jan 05 and it was a little higher then the hot line when hot. Since I didnt take the initiative to check it until now I dont know if it has lost that inch gradualy over the whole time or just recently.

Thanks for the quick replies. Felt like i was driving a time bomb all day worrying something was gonna go wrong.

Edited for retarded grammer and run on sentences

The coolant droping an inch in a 2 year span does not sound terrible, could be evaporation?

Yeah hopfully it was just evaporation. I think I'll wait until either spring break or summer when we go to western washington to visit the in-laws so I can use their garage to change the LIM gasket. Thanks for the help.