Question2003 Elantra- noticed engine light on and temperature guage running lower than normal.
Saw something on net about computer checking resistance of sensors. Is this sensor bad and making light come on? Car runs great, 55K, no problems, smooth engine, good pep, AC on all year (Florida).
Left dome light on overnight, but did not kill battery and had quick start next AM. Help?
AnswerHi, Dave. The ECM (engine control module) checks the warm-up time for the vehicle. If it takes too long to reach operating temperature, the ECM will store a diagnostic trouble code (P0128 in this case, I believe) and turn on the check engine lamp. This could be caused by a stuck open thermostat, but it's unlikely to be the coolant sensor, because the gauge and computer are on different circuits.
At this point, it's also possible there's more than one problem. Checking the ECM for trouble codes will give information about the type of failure seen. You could go by AutoZone or someplace else that reads codes for free, but since you're within the warranty period, it's probably better just to go straight to the dealer and make them aware of both the low temp and check engine lamp.
You can discount the dome lamp as a possible cause. If the vehicle started normally, the battery wasn't significantly drained.
