I'm creating this thread as a means of compiling a one-stop reference for defining, locating, and identifying Diesel Emissions Sensors for the Cruze, including part numbers and links to How To threads for repair/replacement instructions. Additional information is welcomed, as well as corrections to the material here. I will update the OP continuously with newly-discovered or corrected information.
O2 Sensor #1 (Lambda - pre-DPF) - Located at the entrance to the DPF unit, below NOX#1 and EGT#1 sensors. Part#: 12644786
Exhaust Gas Temperature Sensor #1 (pre-DPF) - Next to (right of) NOX#1 Sensor, between Turbo and DPF. Original Part#: 55583113, New Part#: 55598259
Exhaust Gas Temperature Sensor #2 (mid-DPF) - Inserts onto front of the DPF unit at the border between the Oxidation Catalyst stage and the Particulate Filter stage. Part#: 55581035
Exhaust Gas Temperature Sensor #3 (pre-SCR) - upstream of DEF injector Part#: 55581034
EGR Temperature Sensor - Located on Exhaust Manifold at exit of cylinder 4. Part#: 12634536
Differential Pressure Sensor (DPF Pressure Sensor) - A single sensor module that inserts at two points (pre-DPF and post-DPF) and measures the difference in pressure between the two points to identify when a re-gen of the DPF is necessary. Part#: 55570092
NOX Sensor #1 ("Forward," pre-DPF, or pre-SCR) - First Sensor in the exhaust system, next to (left of) O2 Sensor, between Turbo and DPF. Measures Nitrous Oxide in exhaust in order to regulate DEF injection, and monitors SCR performance in conjunction with NOX Sensor #2. (The photo is currently mis-labeled, I will update as soon as I have a chance.) Original Part#: 12641556, New Part#: 12662658
NOX Sensor #2 ("Rear" or "post-" SCR) - Second-last sensor in the exhaust system; located immediately upstream of the Particulate Matter Sensor (on the right of it if looking from the passenger side of the vehicle); inserts on exhaust pipe just forward of the rear wheels, along the mid-line of the vehicle, across from the fuel filter. Module end of the sensor can be found to the rear of the Fuel Filter (on your right if you slide under the car from the passenger side). Measures Nitrous Oxide in exhaust after DEF injection to monitor performance of SCR. For a How To article on replacing this part, see the article on replacing the Particulate Matter Sensor, found at http://www.cruzetalk.com/forum/169-...58-how-replace-diesel-particulate-matter-sensor-exhaust-particulate-sensor.html. Follow the same procedure outlined for the Particulate Matter Sensor, but replace the other sensor of the pair. Original Part#: 12641557, New Part#: 12662659
Particulate Matter Sensor (a.k.a. Exhaust Particulate Sensor) - Last sensor in the exhaust system; located immediately after NOX Sensor #2 (on the left of it if looking from the passenger side of the vehicle); inserts on exhaust pipe just forward of the rear wheels, along the midline of the vehicle, across from the fuel filter. A wire runs from this sensor to a control module that is mounted next to the fuel filter. The module and sensor are replaced together as an assembly. How To available at: http://www.cruzetalk.com/forum/169-...58-how-replace-diesel-particulate-matter-sensor-exhaust-particulate-sensor.html Original Part#: 12655962, New Part#: 12661098
O2 Sensor #1 (Lambda - pre-DPF) - Located at the entrance to the DPF unit, below NOX#1 and EGT#1 sensors. Part#: 12644786

Exhaust Gas Temperature Sensor #1 (pre-DPF) - Next to (right of) NOX#1 Sensor, between Turbo and DPF. Original Part#: 55583113, New Part#: 55598259
Exhaust Gas Temperature Sensor #2 (mid-DPF) - Inserts onto front of the DPF unit at the border between the Oxidation Catalyst stage and the Particulate Filter stage. Part#: 55581035
Exhaust Gas Temperature Sensor #3 (pre-SCR) - upstream of DEF injector Part#: 55581034

EGR Temperature Sensor - Located on Exhaust Manifold at exit of cylinder 4. Part#: 12634536
Differential Pressure Sensor (DPF Pressure Sensor) - A single sensor module that inserts at two points (pre-DPF and post-DPF) and measures the difference in pressure between the two points to identify when a re-gen of the DPF is necessary. Part#: 55570092
NOX Sensor #1 ("Forward," pre-DPF, or pre-SCR) - First Sensor in the exhaust system, next to (left of) O2 Sensor, between Turbo and DPF. Measures Nitrous Oxide in exhaust in order to regulate DEF injection, and monitors SCR performance in conjunction with NOX Sensor #2. (The photo is currently mis-labeled, I will update as soon as I have a chance.) Original Part#: 12641556, New Part#: 12662658
NOX Sensor #2 ("Rear" or "post-" SCR) - Second-last sensor in the exhaust system; located immediately upstream of the Particulate Matter Sensor (on the right of it if looking from the passenger side of the vehicle); inserts on exhaust pipe just forward of the rear wheels, along the mid-line of the vehicle, across from the fuel filter. Module end of the sensor can be found to the rear of the Fuel Filter (on your right if you slide under the car from the passenger side). Measures Nitrous Oxide in exhaust after DEF injection to monitor performance of SCR. For a How To article on replacing this part, see the article on replacing the Particulate Matter Sensor, found at http://www.cruzetalk.com/forum/169-...58-how-replace-diesel-particulate-matter-sensor-exhaust-particulate-sensor.html. Follow the same procedure outlined for the Particulate Matter Sensor, but replace the other sensor of the pair. Original Part#: 12641557, New Part#: 12662659

Particulate Matter Sensor (a.k.a. Exhaust Particulate Sensor) - Last sensor in the exhaust system; located immediately after NOX Sensor #2 (on the left of it if looking from the passenger side of the vehicle); inserts on exhaust pipe just forward of the rear wheels, along the midline of the vehicle, across from the fuel filter. A wire runs from this sensor to a control module that is mounted next to the fuel filter. The module and sensor are replaced together as an assembly. How To available at: http://www.cruzetalk.com/forum/169-...58-how-replace-diesel-particulate-matter-sensor-exhaust-particulate-sensor.html Original Part#: 12655962, New Part#: 12661098