joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
Good luck.
Remember, OBDI was essentially proprietary--no standards set, so each manufacturer basically did what they wanted. Commonality came with OBDII.
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- Thread starter Khary23
- Start date
Good luck.
Remember, OBDI was essentially proprietary--no standards set, so each manufacturer basically did what they wanted. Commonality came with OBDII.
- Location
- Rainy side of Washington
And even then, they had a choice! They could use FIVE different standards all implemented within the OBD II standard! SAE J1850 (Pulse Width Modulated signal), SAE J1850 (Variable Pulse Width signal - yeah, same exact meaning as the last one, but slightly different because it's GM instead of Ford...), ISO 9141-2 (async serial, similar to RS232), ISO 14230 KWP2000 (KeyWord Protocol 2000), or ISO 15765 CAN bus!
An OBD II reader just has to support *all* of those to work on all vehicles. The best part? OBD II specifies a subset of what MUST be supported, beyond that, manufacturers can define their own proprietary secret codes and data fields that only mean things to their dealership's scanners.
The sarcastic maxim "standards are awesome because there are SO MANY TO CHOOSE FROM" counts triple in the automotive electronics industry. Thank god most companies just settled down and use CAN bus for most things now.
If you really want to dig in and learn a bunch of arcane OBD II information: http://en.wikipedia.org/wiki/On-board_diagnostics#OBD-II_Signal_Protocols
