Trouble Code P0128: Faulty Thermostat


Although I haven’t experienced this issue thus far, apparently a few of the thermostats that Mazda has installed (the majority of the cooling system is Mazda MX-5, so this is not the Fiat thermostat used on the 500, although some of those have issues as well) onto our Fiat engines have been troublesome (sticking in the open position or opening too soon), which results in the engine warming up to normal operating temperature too slowly.   There a a few clues, that you may observe eventually, that you may have one of these faulty thermostats:

  • the blue engine coolant lamp remains ON for longer than about 5 – 7 minutes after starting your engine that has been off for more than an hour
  • the coolant temperature gauge takes more than 5 – 7 minutes to get to normal operating temperature
  • the CEL (Check Engine Lamp) is ON, and the error code P0128* will come up if an OBD-II diagnostic tool is hooked up to your vehicle

Consider this as an inconvenience issue rather than critical, but don’t ignore it either. This is obviously a warranty item that your dealer will fix for you, but the thermostat is very difficult to get to at the rear of the engine, and they seem to be on back-order, so you are advised to ask the dealer to pre-order the following parts and verifying their arrival (on hold in your name) prior to your service appointment for the repair, so that your vehicle isn’t kept for a couple of weeks waiting for said parts:

  • replacement thermostat (Part # 68320858AA)
  • vacuum pump gasket (Part # 68140726AC) >> perhaps the vacuum pump has to be removed in order to get to the thermostat?
  • (thought there was also an electrical connector?, but can’t find mention of it right now)

It is OK to drive the vehicle in this condition while you are waiting for your service appointment, but as the manual advises you to do when the blue coolant lamp is ON, go easy on engaging the turbo  😉  for the longer duration that that lamp is illuminated.


Apparently, the 124 Spider’s ECU (also known as the Power Control Module (PCM)) is being flashed at some dealerships to alter the engine operating temperature vs. time algorithm somewhat, so that the CEL (and the P0128 trouble code*) isn’t illuminated for marginal thermostat behavior.

*     P0128 Trouble Code:  Indicates that the coolant temperature has not achieved the required thermostat regulating temperature (engine operating temperature) within a specified amount of time after starting the engine.



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