If the first mechanic would have done something to the coolant temperature sensor the Engine Computer would have detected it right away and turned on the Check Engine light before the car left their shop.

I can't speak to the cost of the first service but a coolant temperature sensor installed for a Chrysler product is around $40.00 not including any diagnostic time. The code you have though suggests it's not a failure of the sensor, which is rare. It sounds more like the thermostat is opening too quickly and not letting the engine reach proper operating temperature. Depending on which engine you have, the thermostat is more time-consuming to replace than the temperature sensor.

This might not apply but you should be aware that there is a long list of things that must occur for a diagnostic code to set. One of those things is certain other codes can not already be set in memory. That's because the computer compares many sensor readings and other things to each other to figure out when something is wrong. As an example, it knows that when the engine has been off for more than six hours the intake air temperature sensor and the coolant temperature sensor had better be reading the same temperature. If there is already a code set for one of them, the computer has nothing to check the other one against so it can't set certain codes related to it. That is real frustrating to GM owners and their mechanics. If an anti-lock brake problem is ignored long enough, a second problem can develop but the second code won't set until right after the first problem is repaired. No one had any idea there was a second problem waiting to set a code. The mechanic is frustrated because he has to tell you more diagnosis and parts are needed beyond the original estimate, and you're frustrated because you're certain the mechanic is ripping you off.

I'm pretty sure your two problems aren't related though because it wouldn't have taken three weeks for the new code to set. If the thermostat really is all that's wrong you should notice the air from the heater is not as hot as normal. Also, if you have a temperature gauge on the dash, it will be reading lower than normal.

Answered by caradiodoc (expert)
17,643 answers provided