| CPC F02D 35/0015 (2013.01) [F01N 3/021 (2013.01); F01N 11/002 (2013.01)] | 7 Claims |

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1. A diagnostic device for an exhaust gas aftertreatment device that has a filter for collecting fine particles from exhaust gas of an engine and is provided in a vehicle, the diagnostic device diagnosing a malfunction in the exhaust gas aftertreatment device, the diagnostic device comprising:
a temperature detection device that detects a filter inlet-side temperature and a filter outlet-side temperature;
a differential pressure detection device that detects a differential pressure between a filter inlet-side pressure and a filter outlet-side pressure;
an intake air pressure detection device that detects an intake air pressure of the engine; and
a controller that determines the malfunction in the exhaust gas aftertreatment device based on values detected by the temperature detection device, the differential pressure detection device, and the intake air pressure detection device,
wherein the controller determines the malfunction in the exhaust gas aftertreatment device based on an index, and
wherein the index is a value based on a ratio between the filter inlet-side temperature and the filter outlet-side temperature and a ratio between the differential pressure and the intake air pressure of the engine.
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5. The diagnostic device for the exhaust gas aftertreatment device according to claim 1, wherein the controller performs processing relating to information security on at least one of the values detected respectively by the temperature detection device, the differential pressure detection device, and the intake air pressure detection device.
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