Car guides: faults, mileage, DPF and battery

Plain-language guides on checking a used car's electronics, the check engine light, DPF soot load and battery health.

• Has the mileage been rolled back? How to check mileage from the car's computer

  Mileage check from the car's computer: the odometer is compared with the modules' own records. Report labels, signs of a possible rollback and the limits.

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• An electronics checklist for buying a used car

  Buying a used car? What to check on the electronic side: faults, fault history, distance since the last clear, the mileage label, modules, battery and DPF.

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• TRAMER, PTT mileage record, professional inspection and OBD: what does each show?

  TRAMER, the PTT mileage record, an inspection and an OBD scan answer different questions. What each shows, what it doesn't, how to use them together.

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• Why is the check engine light on? Steady yellow vs. flashing

  Why is the check engine light on, and what do a steady yellow light and a flashing one tell you? Possible causes and what to do when it comes on.

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• Does clearing a fault code fix the fault? When to clear, and when not to

  Clearing a fault code doesn't fix the fault; if it persists, the code and warning light return. When to clear, when not to, and how every clear is logged.

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• Were fault codes cleared before the sale? How to read "Since codes were cleared"

  Were a used car's fault codes cleared recently? What the report's "Since codes were cleared" row shows, and why a low value is a sign to ask about.

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