Reading: choosing the protocol and understanding the OBD on UDS report

Where: Remote sessions › Diagnostics › Read vehicle › Protocol

By default the read uses “Automatic (recommended)”: the unit tries with read-only requests and picks the protocol that answers. Leave it that way unless you know which protocol the vehicle uses.

1. Choosing the protocol by hand

1. In “Read vehicle”, open “Protocol” and choose one: CAN (ISO 15765) at 500 or 250 kbit/s, 11 or 29 bits; K-Line KWP2000 or 5-baud; J1939 at 250 or 500 kbit/s; or DoIP (Ethernet).
2. Choose the unit and the kind of read and start reading as usual.
3. If the vehicle does not answer with that protocol, you see “Link failed”: go back to “Automatic (recommended)”.

It helps when automatic detection is slow or gets it wrong: for example, a truck you know speaks J1939 at 500 kbit/s. With CANopen machinery diagnosis the protocol is not chosen. In the app you have the same “Protocol” field in “Read vehicle”.

2. Notices while reading

• “The control unit asks for more time to answer”: wait, the read goes on.
• “The control unit is busy; the device stopped retrying”: that control unit did not give the value; repeat later.
• “Failed” on a value: the control unit said it had it but did not deliver it.

3. Vehicles with OBD on UDS (OBDonUDS, SAE J1979-2)

• The most recent vehicles speak OBD on UDS. The control unit's protocol shows it with “· OBDonUDS (SAE J1979-2)”.
• “Readiness by monitor group”: each group shows “Complete” or how many monitors are missing. If some are missing, the vehicle may not pass inspection until it completes its drive cycles.
• Each fault shows its “Readiness group” and, if any, its test results and the monitor that watches it.
• “Supported OBD routines (service 08 equivalent)”: they are only listed; the read never runs them.

Tip: When in doubt, use “Automatic diagnosis”: it detects, identifies and reads everything without you choosing anything.

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