About a month or so ago my check engine light went on and the same time I was noticing that the temperature gauge was taking time to get to normal running temperature. I ran the code and it came up with P2181 which suggested replacing the Temperature Sensor or Thermostat. I tried the temperature sensor but that did not change anything so I moved on to the Thermostat. That fixed the problem and I cleared the code and the car has been running great. Today I went to get it Smoged as I am selling it and the test failed. The owner of the smog shop told me that it was because the P2181 code was still in the system. I told him that I recently addressed the fault. He told me that even though the check engine light is gone it takes a bit of driving until the permanent code is cleared. I recently purchased a new car so I rarely drive the car. Does anyone know how many miles I need to drive in order for the code to disappear from the system or if there are any workarounds?