On-board diagnostics (OBD) monitor the various systems in automobiles and trigger various alerts when a system fails or falls short of performance requirements. Two types of OBD exist: OBD1 and OBD2. They are also known as OBD-I and OBD-II respectively.
The baud rate, or speed at which an OBD communicates with the other systems, is significantly higher in an OBD2. An OBD1 system's hardware is older, providing slower communication speeds.
The OBD hardware contains lists of error codes that the system can check and display if necessary. OBD1 error codes are dependent on the make and model, and thus errors were harder to determine car to car. OBD2 systems standardize the error codes, making generic codes which exist in all OBD2 systems despite different makes and models.
OBD1 systems only signal an error code if an entire circuit or component of the vehicle's system fails as a whole. OBD2 systems use diagnostic tools to measure performance requirements and display an error if requirements are not met regardless of circuit or component failure.
