A Mazda CX-5 diesel with a blocked DPF the seller called 'just a warning light'
OBD-II live data and a road test under load saved a Parramatta family $6,400
2019 Mazda CX-5 Maxx Sport 2.2L Diesel — 96,800km
What the seller said
'It's just a warning light from a long trip last weekend. A reset at the dealer and it's fine.' The car presented immaculately — full service history at an independent mechanic, two adult owners, garage-kept.
What the OBD-II scan tool found
- DPF soot loading: 142% — well above the 100% threshold where forced regen becomes impossible without removal.
- 14 failed active regen attempts in the rolling fault history.
- Differential pressure sensor reading 38mbar at idle — should be under 10mbar.
- Torque-converter lock-up shudder at 60–80km/h under light throttle — confirmed on road test.
- EGR cooler showing carbon build-up via borescope through the intake.
Repair cost estimate from the report
| Item | Estimate |
|---|---|
| DPF forced regen + EGR clean | $1,800 |
| Torque-converter rebuild or replacement | $3,600 |
| Differential pressure sensor | $420 |
| Diagnostic + labour buffer | $580 |
| Total realistic remediation | $6,400 |
Outcome
The buyer took the report to the seller. After 48 hours of back-and-forth the seller agreed to $22,590 — exactly the asking price minus the repair quote. The buyer had the DPF and EGR done at a Mazda specialist within a fortnight. The torque converter is being monitored.
"I would have driven it home and binned it within 5,000km. The report literally paid for itself nineteen times over."
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