I'd suspect the thermostat first. If you have a thermometer that you can stick in the radiator you can verify it's not up to 195 degrees. That will also show up in "live data" if you're using a scanner that displays sensor readings.
Each car model is different but as a general rule when the coolant gets to around 160 degrees, the Engine Computer switches to closed loop. All that means is at colder temperatures the fuel metering is based on sensor readings and pre-programmed values, but once that magic temperature is reached it is assumed the oxygen sensor is up to 600 degrees where it starts to work properly. Then, in closed loop, the computer uses the O2 sensor's readings to fine tune the fuel / air mixture.
There is a set period of time the computer will wait for the engine to get to that 160 degrees. I DO know that was six minutes on older Chrysler engines. They never reached that temperature in six minutes in winter and it did set a code but that one didn't turn the Check Engine light on.
If I'm right about the thermostat, you might find the air from the heater is not particularly hot although that might be hard to tell in the summer. A better test might be to feel the heater hoses. Normally they are too hot to hold onto for very long. If you can hang onto them without feeling uncomfortable, they're too cool.
Sunday, June 5th, 2011 AT 12:39 AM