Faulty 4C Pressure Switch
4C Pressure Switch harness is open or shorted
4C Pressure Switch circuit poor electrical connection
Open Transmission Control Relay
Faulty Transmission Control Module (TCM)
Engine Light ON (or Service Engine Soon Warning Light)
The Diagnostic Trouble Code (DTC) P0988 will set if 4C (4th clutch) pressure switch is open or closed at the wrong time in a given gear. For example, this DTC would be set if the 4C pressure switch came on while the transmission was in second gear. The transmission system will default to an immediate shutdown routine.