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Possible causes: 1. The soot sensor is incorrectly installed. The angle with respect to the exhaust gas flow direction should be 85° ± 5°. 2. A protrusion of the neck into the exhaust gas system can influence the appropriate flow through the protection tube and can affect the sensitivity. 3. In case of a DPF that is leaking and a malfunctioning SCR: NH3 concentrations cNH3>25 ppm have an influence on the sensor current through the deposited particulate matter. Therefore NH3 concentrations that high could lead to a false fail detection. 4. Broken soot sensor T270.