all of the C4 (C4-1 through C4-5) codes are accelerator sensor related. usually this is a bad connection at the sensor but can be caused by moisture in one of the connectors between the sensor and the engine controller. check the connectors for secure locking and make sure no moisture is present. this can also be caused by over rotation of the sensor (ie pedal to the floor with stop bolt missing or loose). remove the battery cable for about 15 secs after you check for problems and this should clear the code.