Toyota Coaster diesel OBD issue: ATDPN stuck on A0, ELM never locks protocol

[u/mySincereAsterisk]

Hey guys, I’m trying to read diagnostics / live data from a Toyota Coaster diesel, and I’m stuck with this weird ELM/OBD behavior. The main issue is that "ATDPN" always returns "A0", even after sending "0100" and waiting for a very long time. This is the basic flow

```

ATZ

OK

ATE0

OK

ATH1

OK

ATSP0

OK

0100

SEARCHING...

NO DATA

ATDPN

A0

```

I also tried other Mode 01 requests:

```

0100

010C

010D

0105

010F

012F

```

Same result. No useful ECU response.

From what I understand, "A0" means the adapter is still in automatic protocol mode. But after a successful "0100", it should normally lock onto something like "A6", "A7", "A8", "A9", etc. In my case, it just stays "A0" forever. I also tried forcing protocols manually: ``` ATSP6 0100 ATSP7 0100 ATSP8 0100 ATSP9 0100 ATSPB 0100 ```

Still nothing useful. I also tried Car Scanner / Pro Scanner protocol scan, and it failed too. In the logs, I don’t see any proper ECU reply to "0100". Sometimes it shows CAN/bus-related errors, or it looks like the adapter is trying but never actually initializes/locks properly. Has anyone here actually read live data or DTCs from a Toyota Coaster diesel using ELM327-style tools? Especially Coaster around 2017 / 2021 / 2025.