I have a 2001 Corolla with, I'm not kidding, 33,000 miles. I recently got a P0125 CEL, but the light has since gone off on its own. Nevertheless, the OBD II scanner still picks it up when I scan the car.
I'd otherwise just leave the car alone, but I've notice a serious drop in mpg (last time I calculated it, I was getting only 20 mpg around town). I have replaced the air filter with a K&N, I replaced the MAF with an OEM sensor about 500 miles ago, and my mechanic replaced the oxygen sensor about 2,000 miles ago (however, I don't know whether he replaced with OEM or not).
I just brought the car in for a standard 30K tune-up at a local shop and he didn't notice anything wrong (although I didn't mention the OBD error or the gas mileage problem).
Any recommendations for what I should test / replace? I miss my former superb gas mileage.
-Frank
Reply 1 : P0125 + horrible gas mileage
P0125: Insufficient Coolant Temperature For Closed Loop Fuel Control
Evidently your car is not recognizing that the engine is warming up. Because of this, your car never goes into "Closed Loop" mode. What happens when your car is in closed loop is that your computer starts to use readings from the O2 sensors to adjust the fuel maps. If it stays in open loop, it sticks with a fuel map that isn't very efficient.
When your car is at operating temperature, is your temp gauge showing that temp, or does it stay on C? I'm thinking that your coolant temperature sensor is either not working, unplugged, or one of the wires going to it is broken. Or, your thermostat may be stuck open. Hopefully this helps you.
Kyle
Oh, and I bought my 02 Corolla in September of 09 with 26,000 miles
Reply 2 : P0125 + horrible gas mileage
idk why, but i also have an 01 corolla with 99k miles, and get 25 mpg. if im lucky 30, but rarely. maybe that's just how corollas are programmed?
Reply 3 : P0125 + horrible gas mileage
My 2000 with 60,000 miles gets 30+ MPG in warm weather. I'm in Massachusetts too, and this winter I'm getting 18 to 22 MPG. Perhaps you should wait for a warmer spell and see if the MPG improves before you change anything else. These four cylinders do take longer to warm up, and this winter loss of MPG has been going on since I got the car in 2000.
Reply 4 : P0125 + horrible gas mileage
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Originally Posted by pchalpin 
My 2000 with 60,000 miles gets 30+ MPG in warm weather. I'm in Massachusetts too, and this winter I'm getting 18 to 22 MPG. Perhaps you should wait for a warmer spell and see if the MPG improves before you change anything else. These four cylinders do take longer to warm up, and this winter loss of MPG has been going on since I got the car in 2000.
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Reply 5 : P0125 + horrible gas mileage
Speaking of Codes and bad MPG, our 99 VE threw a 115,. 120,125, and 171 code the last time I scanned and we're getting like 20MPG. Might have something to do with the fact that I'll bet the car still has the original upstream O2 Sensor on it. I would be curious to know if O2 sensors age regardless of mileage on the car, possibly explaining some of your problems. Wouldn't hurt to test it, that's for sure. BTW, mine was wacko with the millivolt readings.
DM&FS
Reply 6 : P0125 + horrible gas mileage
winter blend fuel sucks
Reply 7 : P0125 + horrible gas mileage
i know some one who lost about 10mpg over the course of 3 months. he noticed the the car would take forever to warm up and when he had a mechanic look at the temp sensor it was determined that that was the problem. after a new one was put back in the car got better gas mileage and warmed up like it used to.
Reply 8 : P0125 + horrible gas mileage
Our motor warms up normally and the ohm reading on it cold was 5.4k at 30 degrees F. Wit h it spozed to be 2-3k ohms at 70 F, I think we're alright. That thing is a bear to get at BTW!!!
Reply 9 : P0125 + horrible gas mileage
I live in mass, and in the winter I get 20-25 mpg, in the summer 30mpg + easy. It's probably the weather
Reply 10 : P0125 + horrible gas mileage
In past winters we've still been over 30 mpg during highway driving but not lately this winter. We get 36 with the AC on and driving 65 with 3 sp automatic in summer.
DM&FS
Reply 11 : P0125 + horrible gas mileage
I've used Shell gas for years and I get 26-30mpg depending on the time of year, but lately I switched to Exxon be cause the Shell pumps at my station were adjusted where they flow too slow. I went through two tanks of Exxon gas which has 10% ethanol. The first tank I saw the mileage went down from 30-27mph. The second tank it went down to a measly 23mpg which has never happened before so I switched back to Shell gas at another station with faster pumps and I'm expecting to see the mpg return to normal since there are no engine issues causing it that I can detect. So from my experience if any of you are using Exxon gas that could be one of the reasons you have low mpg and it would be worth trying another brand.
Reply 12 : P0125 + horrible gas mileage
i just got a 2001 corolla S 6 days ago. it had overheating issues which threw codes. the only issue was the thermostat sticking and missing peices off of it. changed it and had no cooling problems since. check engine light did go off however, it came back on the next day. my mechanic said that the coolant temperature sensor is possibly damaged from the overheating. so my next mission is to replace it.
Reply 13 : P0125 + horrible gas mileage
Hmmm... I never noticed this sort of problem with my car. I've got a 2002 with 130K miles on it and I get between 32 - 36mpg highway driving winter or summer regardless, depending on how aggressively I drive. The engine takes only a few minutes to warm up to normal operating tempurature (depending on how cold it is outside, it can take up to 15 minutes), no issues with any of the sensors, etc.
Do the 2001 - 2002 model years have better tuned engines or am I just lucky that I haven't seen abysmal fuel economy?
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