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OBD-II PIDs (On-board diagnostics Parameter IDs) are codes used to request data from a vehicle, used as a diagnostic tool. SAE standard J1979 defines many OBD-II PIDs. All on-road vehicles and trucks sold in North America are required to support a subset of these codes, primarily for state mandated emissions inspections .
The typical modern TCU uses signals from engine sensors, automatic transmission sensors and from other electronic controllers to determine when and how to shift. [2] More modern designs share inputs or obtain information from an input to the ECU, whereas older designs often have their own dedicated inputs and sensors on the engine components.
OBD-II is an improvement over OBD-I in both capability and standardization. The OBD-II standard specifies the type of diagnostic connector and its pinout, the electrical signalling protocols available, and the messaging format. It also provides a candidate list of vehicle parameters to monitor along with how to encode the data for each.
It is able to do this by flashing a check engine light on the car's instrument panel and storing the information about a malfunction in its memory. When taken to a service center, the ECM uses this same light to "talk" to the mechanic through a flashing code that indicates where the problem is. On Cadillacs, the proper code is digitally displayed.
Unified Diagnostic Services (UDS) is a diagnostic communication protocol used in electronic control units (ECUs) within automotive electronics, which is specified in the ISO 14229-1. [1]
Keyword Protocol 2000, abbreviated KWP2000, is a communications protocol used for on-board vehicle diagnostics systems (OBD). This protocol covers the application layer in the OSI model of computer networking. The protocol is standardized by International Organization for Standardization as ISO 14230.
The data link connector (DLC) is the multi-pin diagnostic connection port for automobiles, trucks, and motorcycles used to interface a scan tool with the control modules of a given vehicle and access on-board diagnostics and live data streams.
The description of Mode 3 DTC parameter data seems to be specific to CAN-bus OBD-II ECUs. Older, pre-2003 OBD-II ECUs (i.e., J1850 VPW/PWM, ISO 9142-2 and Keyword 2000) pack DTC data into multiple OBD-II response packets somewhat differently. --Bruce D. Lightner 17:00, 14 December 2011 (UTC)