Example: OBD2 J1979 CAN Data

With Powervisions Free Form CAN application it is possible to communicate with a vehicles OBD2 port using J1979 protocol.

In it's simplest form, an 11 bit PID Request message is sent to the vehicles ECU then the Reply messages are received and decoded. 

Note: Powerview displays do not have all the features required by governmental agencies to be used as a primary dash display and are not to be used in that application.

Download the Example created in PV version 7.78

How it Works:

• All messages are 11bit id
• CAN data rate is 500k
• Byte order is Big Endian
• Send 0x7DF PID Request message for each parameter of interest
• Decode multiplexed Reply messages 0x7E8 using filtering based on value of first three bytes
• See Wikipedia for more details of PID values and scaling

Example - Request Message - 0x7DF - RPM

• ID = 0x7DF  - Request PID message
• Byte 1 = 0x02 - Number of data bytes to follow
• Byte 2 = 0x01 - Service Mode - show current data
• Byte 3 = 0x0C - PID Requested - Engine Speed
• Byte 4 - 8 = 0xCC - Not used - bit stuffed with 0xCC 

Example - Reply Message - 0x7E8 - RPM

• ID = 0x7E8 - PID Reply Message
• Byte 1 = 0x04 - Number of data bytes to follow
• Byte 2 = 0x41 - Service Mode + 0x40
• Byte 3 = 0x0C - PID Reply - Engine Speed 
• Byte 4 = xxx - RPM MSB
• Byte 5 = xxx - RPM LSB
• Byte 6 - 8 = Not used

Limitations:

There are a limited number of standard PID definitions published, all others appear to be proprietary to the vehicle manufacturer and might be costly to obtain.