- Visual/Physical Underhood Inspection

If the ``Check Engine'' lamp is illuminated, or if a malfunction is suspected in the EGR or TCC systems, all system wiring and vacuum hoses should be inspected visually and repaired if found damaged, loose, disconnected or improperly routed. If a visual inspection does not reveal the cause of the malfunction, perform the ``Diesel System Diagnostic Check,'' Fig. 1, following all steps in order and correcting any malfunctions found. Refer to Figs. 2 through 14, for sub-system diagnostic charts and Figs. 15 through 19, for system schematics and ECM terminal identification.