"Check Engine" light on when driving

[pat_b900]

Hey everyone,

I am having a small problem while driving in my Saab 900 (1997) i noticed that some how the temperature starts decreasing, which to my knowledge is not actually possible. This has happened to me about 4 times in the past 3 weeks.

As the temperature starts to drop, the check engine light comes on in the dash, however nothing is visually wrong and there is no affect to the cars driving ability. ie no power loss or no issues as far as i can tell.

Please help me =(

Pat

[ted182]

So the check engine light goes off when you drive the car again (shut it off)? My guess would be the thermostat, which controls the temperature by turning on and off the water pump, or the sensor that detects the temperature and controls the temp gauge. If the thermostat fails, the car will not heat up or will not maintain temperature. I suspect that the sensor that operates the heat gauge also sends information back to the ECU, which subsequently turns on the check engine light when the car cannot maintain a temperature. It seems quite likely that either the thermostat is not working, or that it is working fine and a sensor is broken. I should also point out that these two things may infact both be the thermostat, in which case, I would recommend replacing the thermostat. Either way, a good place to start.