OBD II and what about OBD I

Since the late '70's early '80's vehicles have been equipped with sophisticated electronics to control vehicle emissions and performance.


Through the years several systems have been used, and keeping up with the differences from year to year was a real chore, to say the least. Multiple scanners that attached to the vehicles on-board computer systems were needed, and it was not uncommon for the scanner to become obsolete from model year to model year. These were the days of the "pre-OBD I "(On-Board Diagnosis-First design) systems.


Beginning in '88 CARB (California's Air Resources Board) and the EPA (Environmental Protection Agency) required vehicle manufactures to include a "self diagnostic" program capable of identifying an emission related fault in the On-Board Computer systems. The first generation of On-Board Diagnostics came to be known as OBD I. The CARB conducted studies on the OBD I vehicles and found that the system was not capable of detecting an emission related component unless it had failed. The components that had not failed completely were unable to set a DTC. Also, it was found that some systems not being monitored had failed and yet the vehicle would pass an Emissions Test as the failed part would not be a factor unless the vehicle was being driven or under a load. The CARB and the EPA passed new laws that would address the problems found during the OBD I case study. These new laws and requirements are known as OBD II. Since mid-'94-'95 some vehicles were equipped with the second design, OBD II systems. In '94-'95 only select models were equipped with this new system, and in '96 every vehicle sold in the United States were equipped with the OBD II system. You might be asking, ok, so what? Well, this was the single and largest improvement made to diagnosis and repair of the On-Board Computer systems since their introduction. The DLC (Data Link Connector) that a scanner attaches to, is virtually the same for every vehicle, and the "Generic" DTC's (Diagnostic Trouble Code) are the same for every vehicle. The terminology was changed to terms that would be used by all manufactures. Before this, the computer (PCM), for example, could have been called a Processor, ECU, Control Module, ECM, etc. To know what the name of a part on a specific system was called or how it functioned, or was located, was tough when you worked on multiple vehicle models.

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