There are a couple of other red flags to look for if you’re hoping to catch issues related to a P0128 error code before the dreaded Check Engine light blinks on, such as noticeably diminished fuel economy on your car, or a malfunctioning heating system. Once that light goes on, however, it means your car’s Engine Control Module or Powertrain Control Module has sent a signal to the On-Board Diagnostic System that some issue is causing the engine to run cooler than it should, and action needs to be taken.
Coolant temp can become an issue because when the car’s engine doesn’t reach its target temperature, it has trouble maintaining fuel economy and controlling emissions. As for what may be causing the code P0128 problem, several components need to be inspected as the function in part monitors the rate at which engine coolant reaches an ideal operating temperature.
If the engine isn’t reaching or maintaining its target temperature, there may be a problem with the cooling fan, the intake air sensor, the coolant temperature sensor, or the thermostat. But you might also receive a P0128 signal if you’re regularly operating the vehicle in areas that experience lengthy stretches of extreme cold, as that may prevent your car from warming up.
