The "service engine soon" light comes on when the PT Cruiser's computer sends an error code for one of the sensors. The only way to get the error code to remain off is to fix the problem before resetting the code. If the PT Cruiser displays several codes that do not seem to be related, plus erroneous codes, the computer itself is probably bad. The computer cannot diagnose itself, so the only way it can communicate that there is something wrong is by sending incorrect and/or erroneous codes.
Plug the code scanner into the data port, which is located under the driver's side dash, just to the left of the steering column.
Press the "Read' button. Write down the codes from the scanner's screen. There could be one or more. Translate the code, using the code book that comes with the scanner. Repair the PT Cruiser as needed.
Plug the code scanner back into the data port after the vehicle is repaired. Press the "Erase" button to erase the codes and reset the computer.