ok my sister has 2002 2.5rs with 180k on it. the car had run great all along except a few months back the car over heated... seemed like a random event. last month the car over heated on her again and she parked it because everyone had said it was a head gasket. Until i got to look at the car myself thats what i thought too, that the heads were just expanding when it was driven hard. I dug the car out of the months worth of snow and drove it all day yesterday. The car ran fine except for the following CEL codes. That went away then came back at one point.
P0328 Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)
P0156 Oxygen Sensor Circuit Malfunction (Bank 2 Sensor 2)
P0157 Oxygen Sensor Circuit Low Voltage (Bank 2 Sensor 2)
P0063 HO2S Heater Control Circuit Low (Bank 2 Sensor 3)
P1872 Rear Left ABS Sensor Signal.... im not sure if thats right?
all of these codes seem related to the car knocking but it seems like just replacing the sensor wont be the fix