What is a Diagnostic Trouble Code (DTC)?
Diagnostic trouble codes (or fault codes) are codes that are stored by the on-board computer diagnostic system. These are stored in response to a problem found in the car by the system. These codes are stored, for example, when a sensor in the car reports a reading that is outside a pre-defined range, e.g. fuel mixture too rich. The codes identify a particular problem area and are intended to provide the technician with a guide as to where a fault might be occurring within a car. The codes should be used in conjunction with the vehicle’s service manual to ascertain which systems, circuits or components should be tested to fully diagnose the fault. Reliance on codes alone Parts or components should not be replaced with reference to only a DTC. The vehicle service manual should be consulted for more information on possible causes of the fault, along with required testing. For example, if a DTC reports a sensor fault, replacement of the sensor is unlikely to resolve the underlying problem
