A flow hood assembly for an engine aftertreatment system having a particulate filter and a selective catalytic reduction device, the flow hood assembly comprising: an outer case defining a cavity, the outer case having an inlet and an outlet formed therein, the inlet and the outlet being spaced apart along a longitudinal axis of the outer case, and a neck section formed between the inlet and the outlet; the inlet being configured for attachment to the particulate filter whereby exhaust gases from the particulate filter enter the cavity at the inlet and flow generally along the longitudinal axis toward the outlet; a socket provided in the outer case in an opposed relationship to the outlet and shaped to receive an injector that introduces a reducing agent into the flow of exhaust gases, the injector having a nozzle that protrudes through an opening in the socket into the cavity, wherein the socket and the outlet are spaced apart and aligned along a lateral axis; the outlet configured for attachment to the selective catalytic reduction device, whereby the exhaust gases and reducing agent leave the cavity at the outlet and enter the selective catalytic reduction device; a baffle provided in the cavity, the baffle reducing a cross-sectional area of the cavity at the neck section; and a deflector member provided in the cavity between the baffle and the socket, the deflector member being inclined towards the socket to direct a portion of the exhaust gases towards the socket and across the nozzle; characterised in that: a sensor for detecting NOx in the flow of exhaust gases is provided at the neck section of the outer case, the sensor having a sensing end projecting into the cavity; and the socket further comprises a mounting section to which the injector is attached, the mounting section being configured such that the nozzle is inclined at an angle of 4 to 6 degrees to the lateral axis when the injector is attached to the socket; and the socket is held fixed to the outer case by a clamp, the socket being rotatable with respect to the outer case when the clamp is loosened. an outer case defining a cavity, the outer case having an inlet and an outlet formed therein, the inlet and the outlet being spaced apart along a longitudinal axis of the outer case, and a neck section formed between the inlet and the outlet; the inlet being configured for attachment to the particulate filter whereby exhaust gases from the particulate filter enter the cavity at the inlet and flow generally along the longitudinal axis toward the outlet; a socket provided in the outer case in an opposed relationship to the outlet and shaped to receive an injector that introduces a reducing agent into the flow of exhaust gases, the injector having a nozzle that protrudes through an opening in the socket into the cavity, wherein the socket and the outlet are spaced apart and aligned along a lateral axis; the outlet configured for attachment to the selective catalytic reduction device, whereby the exhaust gases and reducing agent leave the cavity at the outlet and enter the selective catalytic reduction device; a baffle provided in the cavity, the baffle reducing a cross-sectional area of the cavity at the neck section; and a deflector member provided in the cavity between the baffle and the socket, the deflector member being inclined towards the socket to direct a portion of the exhaust gases towards the socket and across the nozzle; characterised in that: a sensor for detecting NOx in the flow of exhaust gases is provided at the neck section of the outer case, the sensor having a sensing end projecting into the cavity; and the socket further comprises a mounting section to which the injector is attached, the mounting section being configured such that the nozzle is inclined at an angle of 4 to 6 degrees to the lateral axis when the injector is attached to the socket; and the socket is held fixed to the outer case by a clamp, the socket being rotatable with respect to the outer case when the clamp is loosened. a sensor for detecting NOx in the flow of exhaust gases is provided at the neck section of the outer case, the sensor having a sensing end projecting into the cavity; and the socket further comprises a mounting section to which the injector is attached, the mounting section being configured such that the nozzle is inclined at an angle of 4 to 6 degrees to the lateral axis when the injector is attached to the socket; and the socket is held fixed to the outer case by a clamp, the socket being rotatable with respect to the outer case when the clamp is loosened.