OBD-II and ELM327 (2), the underlying interface of ELM327

Go to Google play and search keyword of "ELM327 Terminal", all of them were similar, you can just pick arbitrary of one. If you really had some difficult of selection, this one looks beautiful and just updated recently




After connecting the tool with ELM327 and car, type "0902" in the tool to read the VIN code. These PIDs (0902) were industrial standard, and all cars shall implement it. Here's some useful PIDs. That's why HUD (head up display) can connect to all brands of cars with OBD2 connector

  • 01 0D: car speed
  • 01 0C: engine RPM

Here's the 0902 query response of my car in the APP. If interested, decode it :-)
  • 7E8 08 01 14 49 02 01 59 56 41
  • 7E8 08 21 44 5A 41 38 42 44 48
  • 7E8 08 22 32 30 37 36 36 38 32
A lot of people read CAN bus by Torque, but only few people read the ELM327's capability document. Check out ELM327 website and download their AT command list, that's all the capability it had. It had different capability in various versions


Probably because of its popularity (or historical reason), ELM327 command becomes de-facto standard. All Android applications that communicates with car assume it's talking with an ELM327 adapter. On the other hand, if some company want to develop OBD-II probe to general users, it also implements ELM327 command set. Then the probe can connect with all existing SW (even it's NOT a ELM327)

In China, they used 8051 to made their own ELM327 (or just changed the string). However, ELM327 never had v1.5. Quite interesting !!










SW (APP) developer would use less special command to have the best compatibility. In practice, reading engine RPM, speed, fault code does NOT need special command. So these probes actually had very good compatibility with existing SW

If you want to know which one of the probe is better... I probably can't tell you. After all, I didn't try a lot of units. But I can share with you what happens if there's some bad device on CAN bus in later articles

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