This Preliminary Information communication provides information to the technician the steps to diagnose and repair vehicles with a Service Engine Soon Malfunction Indicator Lamp on. Technician may find a Diagnostic Trouble Code P0300. After performing all published Service Information diagnostics and a solution has not been made technician should perform the "Cylinder Leakage Test" procedure in SI and document all leakage rates on the repair order. If a leaking intake valve is found, replace the cylinder head and valves by following the latest versions of 07-06-01-018 (Regular Production Option Code LL8 4.2L), 06-06-01-017 (Regular Production Option Codes L52, LK5) and 07-06-01-019 (Regular Production Option Codes LLR, LLV). Before replacing the cylinder head, review the latest version of PIP3940.