Ordered, concise procedure with theory and why each repair step fixes the fault.

1) Safety & prep
- Park on level ground, parking brake, key off. Disconnect negative battery terminal before disconnecting the electrical connector to prevent shorting or ECU transients.
- Tools: basic hand tools, scan tool/OBD adapter that reads air-mass or intake-air parameters, digital multimeter, MAF cleaner aerosol (not carb cleaner), soft lint-free brush (optional), nitrile gloves.

2) Where the MAF is and what it does (theory)
- Location: inline in the intake between the air filter box and turbo/intercooler on Hino Super F GH1H. It measures the mass of air entering the engine so the ECU can calculate fuel quantity, EGR rate and injection timing.
- Principle (hot‑wire/hot‑film type used on most diesel MAFs): a sensing element is electrically heated. As incoming air flows past it, it cools the element. The sensor electronics increase heating current to keep the element at a constant temperature. The current required (or resulting voltage signal) is proportional to mass airflow (not just volume), so the ECU gets a direct measure of air mass.
- Why accurate reading matters: ECU uses mass air to compute fuel pulse width; incorrect reading -> wrong fuelling (rich/lean), rough idle, poor cold start, increased smoke, high emissions, limp mode.

3) Symptoms and initial diagnostic logic
- Common symptoms: poor idle, stalling, black smoke, fuel economy drop, check engine light (codes P0100–P0104 or manufacturer-specific MAF codes), boost control/EGR faults.
- Start with scan tool: read stored codes, and live MAF reading (g/s, kg/h or V) at key states: key on engine off (KOEO), idle, rev, and steady cruise. Note expected behaviour: low value at idle, increases smoothly with RPM/boost. Jumpiness, zero reading, or maxed out value indicate sensor/electrical/air-leak problem.
- If MAF reads zero and ECU uses MAP fallback, look for open power/ground or broken wiring. If MAF reads low but wiring OK, suspect contamination or sensor drift.

4) Visual inspection
- Inspect intake piping for leaks, cracked boots, loose clamps, or bypasses before/after sensor — air leaks change true airflow but leave MAF signal unchanged relative to actual intake, causing fueling errors.
- Inspect sensor housing for cracks, oil/soot buildup, insect/debris contamination, or internal damage.

5) Electrical checks (ordered)
- Reconnect battery briefly or power on with connector attached for tests (be careful).
- Check harness connector for corrosion, bent pins, water ingress.
- With multimeter: verify reference voltage (commonly 5 V) to sensor power pin and good ground at sensor connector. Check signal wire voltage at KOEO and while revving — should change smoothly with airflow. If no reference voltage or no ground, repair wiring/harness.
- Check continuity/resistance of heater element only if manufacturer spec available; presence of open circuit indicates failed element.

6) Cleaning (when contamination is suspected) — ordered steps
- Remove air intake clamps and remove sensor from housing (note orientation). Do not touch the sensing element with fingers or tools.
- Use dedicated MAF cleaner aerosol spray: hold sensor so element faces upward, apply short bursts from ~10–20 cm to clean deposits. Do not soak wiring or electronics. Allow solvent to evaporate fully (~10–15 minutes).
- If heavy deposits, repeat but never scrub the element; use very soft brush only if manufacturer allows.
- Reinstall with correct orientation and torque on clamps. Reconnect electrical connector. Reconnect battery negative.

7) Replacement (if cleaning/electrical repair fails)
- Remove old sensor and fit OEM or correct aftermarket unit. Ensure mating surfaces and seals are clean; replace seals if damaged.
- Reconnect harness and clamps.

8) ECU reset / relearn and verification
- Clear codes with scan tool. Start engine and monitor live MAF readings: should be smooth and appropriate for RPM/load. Verify fuel trims move into acceptable range.
- Road test under load and steady cruise. Re-scan for new codes. Check smoke, idle quality and throttle response.

9) How each repair action fixes the fault — theory linked to action
- Cleaning: removes insulating deposits (oil, soot) from the hot wire/film so convective cooling by airflow returns to designed behavior. That restores the heater current ↔ airflow relationship, so the ECU receives correct mass airflow numbers, correcting fuel calculations and EGR timing and eliminating rich/lean symptoms.
- Electrical repair: restoring reference voltage/ground/signal continuity allows the sensor electronics to power and report correctly. An open/short corrupts signal or yields zero, forcing the ECU into limp/fallback fueling.
- Fixing intake leaks: if leaks are after the sensor (downstream), ECU still uses correct MAF but actual cylinder airflow differs; sealing the system ensures MAF reading again matches actual air reaching cylinders so fueling is correct.
- Replacement: when element or electronics are permanently damaged or out of spec, replacing restores the designed transfer function between airflow and signal; the ECU then calculates fuel correctly.

10) Post-repair checks to ensure permanence
- Inspect upstream air cleaner for oil feeding into intake (PCV or turbo seals) — recurring contamination indicates root cause upstream.
- Check clamps and vibration isolation so sensor isn’t mechanically stressed.
- Verify no EGR or boost control faults remain (contaminated MAF often masks/causes related faults).

Quick troubleshooting flow (one-line each)
- Scan codes → inspect intake for leaks → check connector power/ground/signal → monitor live MAF vs RPM/boost → clean if contaminated → replace if electrical element failed → clear codes and road test.

End.
rteeqp73

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