[Garhfer]

Hey, I've been reading the forums for few months and decided to join in and ask a question myself. I bought my mustang (2004 GT) a few months back heavily modified and just correcting everything to my standards since. Well since I got it (back in September), it keeps throwing the code P0128 every once in awhile which I looked up on the web means "Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)." I don't know exactly why that would throw a code because I would think having my coolant as cool as possible would be good, well anyways I'm just tired of seeing the "Check Engine" light so I was wondering what I could do to correct it besides clearing the DTC codes. Is the thermostat bad or could it just be a lower thermostat than the computer is set for and if so could I use the sct xcal 2 to correct that? (my car came with it and I'm still not exactly sure how to use it and don't want to jack something up with it) Anyways, any help would be appreciated, thanks for your time.

[Timber]

Sounds like the previous owner put a lower temp thermostat in. I'd change it out for the correct one and see if that cures it.

[ibanez570x]

+1 ... similar situation with old car. shop put in an incorrect thermostat and it started throwing similiar codes...