Diesel Sensor Location Guide

Upstream NOx (Sensor 1)

Mounted in the exhaust pipe before the SCR catalyst — typically on the passenger side, downstream of the turbo and DPF.

Downstream NOx (Sensor 2)

Mounted after the SCR catalyst in the tailpipe section. Measures SCR conversion efficiency.

Detroit DD15 NOx Upstream

Passenger side, threaded into the decomp tube upstream of the SCR brick.

PACCAR MX-13 NOx Upstream

Passenger side exhaust, between the DPF outlet and SCR inlet.

Cummins ISX NOx Upstream

Mounted on the aftertreatment inlet pipe, driver side on most Freightliner/Kenworth applications.

DPF Delta-P Sensor (general)

Mounted on the DPF housing or nearby bracket. Two hose ports connect to the inlet and outlet of the DPF filter.

Detroit DD15 Delta-P

Mounted on the passenger side of the aftertreatment housing, near the DPF inlet.

Cummins ISX Delta-P

Mounted on the DPF canister, driver side. Two small rubber hoses run to the sensor ports.

PACCAR MX-13 Delta-P

Passenger side, on the DPF housing bracket. Often near the DPF outlet temperature sensor.

DPF Inlet Temp Sensor

Threaded into the exhaust pipe just before the DPF inlet. Measures exhaust gas temperature entering the filter.

DPF Outlet Temp Sensor

Threaded into the exhaust pipe just after the DPF outlet. Measures temperature exiting the filter.

Turbo Speed Sensor (general)

Threaded into the compressor housing of the turbocharger. Reads turbine wheel speed via magnetic pickup.

Detroit DD15 Turbo Speed

Mounted on the compressor housing, driver side of the engine.

Boost Pressure Sensor (MAP)

Mounted on the intake manifold or charge air cooler outlet pipe. Measures boost pressure entering the engine.

Turbo Inlet Pressure Sensor

Located on the air intake pipe before the turbo compressor inlet. Measures air restriction.

VGT Actuator Position Sensor

Integrated into the VGT actuator assembly on the turbocharger. Not serviceable separately on most platforms.

Fuel Rail Pressure Sensor (general)

Threaded into the high-pressure fuel rail. On most engines, located on the driver side of the head near the injectors.

Detroit DD15 Fuel Rail Sensor

Driver side, threaded into the end of the high-pressure fuel rail near the front of the engine.

Cummins ISX Fuel Rail Sensor

Threaded into the fuel rail on the driver side, near the front of the cylinder head.

PACCAR MX-13 Fuel Rail Sensor

Driver side, mounted at the rear of the high-pressure fuel rail.

Fuel Temp Sensor

Located on the fuel filter housing or fuel return line. Measures fuel temperature entering the injection system.

Crankshaft Position Sensor (general)

Mounted at the front or rear of the engine block near the crankshaft reluctor ring. Reads engine RPM and TDC position.

Detroit DD15 CKP

Front of engine, driver side, near the front cover. Reads the crankshaft tone wheel.

Cummins ISX CKP

Rear of engine, driver side, near the flywheel housing.

Camshaft Position Sensor (general)

Mounted on the front or rear of the cylinder head near the camshaft gear. Reads cam phase for injection timing.

Detroit DD15 CMP

Front of engine, passenger side, near the cam gear cover.

PACCAR MX-13 CMP

Front of engine, driver side, threaded into the timing cover.