Diesel System Diagnostic Check

The Diagnostic Circuit Check ensures "CHECK ENGINE" light works, ECM is operating and can recognize a fault, and determines if any trouble codes are stored. Memory is cleared on the Diesel Electronic Control system any time ignition switch is turned off. Therefore, unless the engine is left running when vehicle is brought in for complaint or code is reset during the diagnostic circuit check, the problem should be considered intermittent. This is the starting point for any diagnosis.