Isuzu Elf 4JJ1 - DPD forced regen aborting on coolant temp rise

Following up on the 6R20/6R10 air-bleed writeup I posted a while back (thanks for the responses on that one).

This time it's an Isuzu Elf (NKR85, 4JJ1). Same kind of story - textbook stuff didn't cut it.

Symptoms:
- DPD forced regeneration aborts partway through
- Coolant temp climbs and triggers the abort
- Exhaust/DPF temp caps out around 300°C (normally 500-600°C)
- No fault codes anywhere

Did all the standard stuff first: exhaust brake shutter check, DPD disassembly/cleaning (13kPa differential pressure, definitely needed), thermostat replacement, radiator replacement. None of it touched the problem.

Turned out to be something completely unrelated to the cooling system - found it after remembering a Hino case involving the fuel dosing injector. Took about 15 minutes to fix once I knew where to look, no parts required.

Wrote the full diagnosis + fix (with photos) here if anyone's stuck on the same thing: https://note.com/seibishi29/n/na658b550f18f

Happy to answer questions in the thread too.