Check Engine Soon Light

My 2004 Mitsibishi Endeavor's check engine soon light came on last night. I took it to Advance Auto and they cleared the light and told me it was due to the fact I was approaching 75,000 miles...well, tonight...the light came back on and I went back...this time they said the meter read..."cooling element below threshold"..what does this mean?

Need to know the code #.

i have this same issue. the code is: P0421

buts the code reads warm up catalyst below threshold

The P0421 is for the catalytic converter, kinda. It could be the upstream O2 sensor on the rear of the engine OR the converter in the REAR manifold...which is a pain in the ass to replace.


The 'cooling element below threshold' is probably a P0128 and probably a thermostat that has fallen apart or stuck open.

To properly diagnose what is wrong, you need to take your car to a mechanic or a dealer. The technician at the dealership or a garage will then hook up the scanner to the car computer and retrieve the stored trouble code(s). Then he (she) will look it up in the service manual provided by a car manufacturer. The service manual contains the list of possible codes (about few hundreds) and describes what each code means and what needs to be tested. The code itself doesn't tell exactly what component is defective - it only indicates where to look, what engine parameter is out of normal range. The technician will have to perform further testing to pinpoint a defective part.