Introduction to On Board Diagnostics (II)

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsIn a case where messages are broken down into more specific fault descriptions for acircuit, component, or system, as is done in complex cases, the manufacturer shouldchoose the fault code most applicable to their diagnosable fault. The messages areintended to allow the manufacturers to use them as often as possible yet still notconflict with their specific repair procedures. Each code should lead to a specificrepair procedure(s).Examples: As a guide to clarify the above points a few examples are given.For manufacturers choosing to implement basic diagnostics that provide generalfault information but depend on service procedures and Off-board diagnostics toisolate the problem, general circuit, component, and system codes will be used.For example, if a fault is detected in in the throttle position sensor circuit, insteadof burdening the OBD II with determining the specific type of fault, a Code P0120would be stored indicating some type of problem with that circuit. The serviceprocedure would then allow the service technician to determine the type of faultand the specific location of the fault. On these types of systems, such as sensors,actuators, coils, and switches, a shorted sensor input, an open sensor input, and evenout of range sensor output would all set the same fault code.