Diagnostic trouble codes, known as DTCs, are alphanumeric codes that a vehicle's computer outputs when it detects a malfunction. These codes are transmitted by a vehicle's on-board diagnostics (OBD) system and can be accessed using a diagnostic scanner that plugs into the OBD connector. Every vehicle made after 1996 comes equipped with an OBD-II computer—the modern OBD system.
Vehicles today are capable of relaying thousands of diagnostic trouble codes to anyone with the equipment to read them. These codes are primarily referenced by auto services. The savvy driver, however, can also reference a car's codes to diagnose a problem and, in the process, possibly avoid an unnecessary trip to the car shop.
OBD technology was initially developed in the late 1970s in an attempt to better regulate car engine emissions. Those early computers, however, were fairly limited in what they could detect. Jump forward 20 years, and OBD computers had taken a mighty leap, with computers able to read and diagnose a far greater number of car functions. By 1996, with the advent of the OBD-II computer, the modern system of diagnostic trouble codes was born. Since then, every car has been equipped with OBD-II connector ports, sometimes referred to as Diagnostics Link Connectors (DLC) or J1962 connectors.
OBD-II systems are capable of outputting thousands of codes. Codes can either be read by a personal diagnostic scanner or by a certified technician at a car shop. If using a personal diagnostic scanner, one can consult a trouble code manual or any one of multiple websites that provide a thorough listing of trouble codes and their translations. Without any sort of reference, anyone who isn't a certified technician would find it difficult to accurately decipher trouble codes.
Diagnostic trouble codes don't only communicate with individuals, they also communicate with the vehicle. For example, certain codes tell a vehicle when to turn on the "check engine" light. Sometimes, the "check engine" light is triggered by a trouble code that indicates serious car troubles. In other cases, the trouble code that caused a "check engine" light might merely be indicating that a fuse needs to be replaced. Thus, having a personal diagnostic scanner can go a long way in helping an individual car owner figure out whether a "check engine" light actually necessitates a trip to the car shop. A diagnostic scanner can also give a car owner the option of turning off the "check engine" light after assessing the diagnostic trouble code.