Code P0116 in your PT Cruiser indicates a problem in the coolant temperature sensor circuit that is causing the coolant temperature to be inaccurate. The most common cause of this code is a faulty coolant temperature sensor but a shorted wiring harness can be the culprit as well and must be eliminated as the cause before replacing the sensor. Using a typical scan tool and a digital volt/ohm meter, available at most auto parts stores, the average do-it-yourself mechanic can diagnose and repair this code in just a few minutes.
Use the scan tool to observe the temperature supplied to the computer by the sensor. Turn the ignition key off and plug the scan tool into the diagnostic port located under the driver's side of the dash between the steering column and driver's side kick panel. Turn the key on and select "DATA" from the menu. Scroll down the sensor data displayed on the scan tool to the "Coolant Temp" sensor reading.
Unplug the coolant sensor located on the front driver's side of the motor. Observe the scan tool sensor reading. If the temperature indicates a very high temperature (over 400 degrees) the wiring is fine. If the temperature is very low (below 0 degrees) trace the wiring through the wiring harness until the short is found and repair it using wire cutters/strippers and butt connectors.
Start the engine and test the resistance of the sensor using a digital volt/ohm meter. Wait 15 minutes and test the resistance. As the engine heats up the resistance should change and get higher. Replace the sensor if the resistance doesn't change or if infinite resistance is displayed.
Turn the engine off and unscrew the old sensor. Screw the new sensor in and tighten it securely with a socket and ratchet. Erase the trouble code using the scan tool and test drive the car to verify that the check engine light doesn't come back on.
