Catalyst System Efficiency Below Threshold (DOC)
The HINO-P0420 (Hino) diesel fault code means: Catalyst System Efficiency Below Threshold (DOC). This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- intermediate
- Estimated cost
- $500-$3,500
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View pilot availability →What Are the Symptoms of HINO-P0420?
- DPF / Regen lamp illuminated
- Progressive derate (5 mph in final stage)
- Frequent request for manual regen
- Reduced power and fuel economy
- Elevated EGTs during regen
What Causes HINO-P0420? (Most Likely First)
- Short-haul urban delivery duty cycle preventing successful regens (Hino 195 box truck especially) Very Likely
- DPF ash load exceeding service threshold (Hino DPF cleaning interval 200K-300K mi) Likely
- Upstream fault (EGR, injector, rail pressure) preventing proper regen temperature Likely
- Failed EGT or differential pressure sensor Possible
- Plugged delta-P sample tubes giving invalid readings Possible
Can I Still Drive with HINO-P0420?
Short distances only. HINO-P0420 is rated serious severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
What does Hino code P0420 mean?
Hino diagnostic trouble code P0420 (Catalyst System Efficiency Below Threshold (DOC)) is a serious-severity fault on Hino medium-duty diesel engines. It indicates a problem in the DPF / aftertreatment that should be verified with a scan tool (Hino DX3 / DX4) before replacing any parts.
Can I drive my Hino truck with P0420?
Short runs may be possible but do not ignore — Hino medium-duty aftertreatment faults cascade quickly into 5-mph derate or no-restart. Schedule diagnosis immediately.
How much does it cost to fix Hino P0420?
Estimated repair cost runs $500-$3,500. Sensor, wiring, and DEF-related repairs fall at the low end; DPF service, turbo, injector, and EGR cooler work fall at the high end and may require dealer-level programming.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose HINO-P0420?
Confirm P0420 on Hino DX3. Capture soot %, ash %, and distance/time since last successful regen.
Attempt manual / parked regen — outlet EGT should exceed 1000°F for 20+ minutes. Failure to climb indicates upstream DOC / HC doser issue.
Remove and clean delta-P sample lines — soot plugs are a recurring cause of bogus P244A/B codes on Hino.
If ash load is over limit, send DPF for bake-and-blow service or replace; ash cannot be regenerated away.
After repair, reset soot counters with DX3 and drive a representative duty cycle to verify regen completes.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
- SAE J2012Diagnostic Trouble Code Definitions (defines P0420 as a generic OBD-II code)
P0420 on Other Platforms
The same code ID appears across other engines, vehicles, and equipment. Diagnostic flow varies by platform — see the matching breakdown:
Which Vehicles Commonly Get HINO-P0420?
- Hino 155 / 155h with J05 5.1L
- Hino 195 / 195h (hybrid) with J05D 5.1L
- Hino 258 / 258LP / 268 with J08 7.7L
- Hino 338 / 338CT with J08 7.7L
- Hino 358 / 358CT (post-2019 J-series / A09C)
- Toyota Dyna / Hino-branded export chassis with J05/J08
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