Abstract: A method and apparatus for diagnosing excessive resistance in an electrical harness of an internal combustion engine. Voltage is applied from a power source (24) through contacts (30a, 30b, 32a, 32b, 34a, 34b, 36a, 36b) and harness leads (26 and 28) to an electrical assembly (20). Electrical assembly (20) includes the load of a first electrical component (23), and by switching means (25) includes the electrical load of a second electrical component (21). An electronic control module (22 or 38) controls switching means (25) and compares the voltage drop across electrical assembly (20) when the second electrical component (21) is switched in or out. By comparing the voltage drops ECM (22 or 38) can determine if there is excessive resistance in the contacts (30a, 30b, 32a, 32b, 34a, 34b, 36a, 36b) or leads (26 and 28).

Abstract: A fault recognition system is implemented as an adjunct to fault determination software of an on-board engine control module (ECM). The ECM activates a "Type A" or "Type B" fault code for each signal received from a plurality of sensors disposed about the engine when that signal exceeds a predetermined threshold. A "Type C" fault is recognized and activated when all of a predetermined group of underlying "Type A" or "Type B" fault codes have been activated. The "Type C" fault is displayed, while the underlying faults may or may not be displayed. The "Type C" fault provides a better and more immediate indication of the source of the engine problem than any of the underlying faults. Only those underlying faults that aid in the recognition of the source of the engine problem are displayed. The remaining faults underlying the "Type C" fault are masked. When the "Type C" fault becomes inactive, any underlying fault codes are unmasked for subsequent evaluation.

Abstract: A system and method for detecting a fault condition in an internal combustion engine utilizes the intake air temperatures at each of a plurality of cylinder sections of the engine. An average value of the plurality of intake air temperatures is compared to each of the individual temperatures at discrete time increments. The rate of change of each intake air temperature relative to the average temperature value is assessed to determine if a valve-related fault condition has occurred. In a further feature of the system and method, a plurality of temperature differential values over several time increments are differentiated. The resulting plurality of differentiated values are integrated, or summed, over the time period, which result is compared to a threshold value indicative of a valve-related failure.

Abstract: A system and method for detecting a misfire condition for a cylinder of an internal combustion engine is based upon the firing times for each cylinder and a comparison of firing times between successive cylinders in the engine firing sequence. A differential firing time parameter represents the result of this comparison and is used a passive test to determine whether a particular cylinder is misfiring. Cylinders identified in the passive test are subjected to an active test in which the cylinder is overfueled by increasing amounts for each engine cycle after commencement of the active misfire test. The change in differential firing parameter for the identified resulting from the overfueling is compared to an active test threshold value indicative of an expected change for a healthy cylinder. A cylinder falling outside this active threshold value is determined to be a bad cylinder.