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OBD General |
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The parameters an values that are readable via the OBD II diagnostics jack are – regarding the emission relevant part – identical. In defining the protocols that are used for transmission, the manufacturers sadly did not agree on a single protocol.
Generally one can say:
General Motors cars and lightweight trucks have SAE J1850 VPW (Variable Pulse Width Modulation)
Chrysler cars and all European and Asian cars have ISO 9141 with KWP (Key Word Protocol)
Ford has SAE J1850 PWM (Pulse Width Modulation).
Latterly the CAN-Bus is uses for communication in many European cars. From 2004 some models exist, that severely limit access of the control units via the K and L lines and use the CAN-BUS primarily.
It has to be considered that not every company that produces in a country uses the corresponding protocol. For example take Opel. Manufacturing of certain models in Germany, parent company GM in America. So the VPW protocol is used. In most European models one can read out data via the ISO protocol.
To determine the protocol used in the own car, one looks at the own diagnose jack.
The following chart should be used for distinction of the protocols. The following contact assignment can suggest the adjoining protocol:
For the sake of completeness should be said, that other pins are used at the cars most of the time; they are specific to a certain manufacturer and have no real relevance for diagnostics via OBD.
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