C Series Acronyms and Abbreviations Section i - Introduction Page i-15 NOx Mono-Nitrogen Oxides NG Natural Gas O2 Oxygen OBD On-Board Diagnostics OEM Original Equipment Manufacturer OSHA Occupational Safety and Health Administration PID Parameter Identification Descriptions ppm Parts Per Million psi Pounds Per Square Inch PTO Power Takeoff REPTO Rear Power Take Off RGT Rear Gear Train rpm Revolutions Per Minute SAE Society of Automotive Engineers SCA Supplemental Coolant Additive SCR Selective Catalytic Reduction STC Step Timing Control SID Subsystem Identification Descriptions TDC Top Dead Center VDC Volts of Direct Current VGT Variable Geometry Turbocharger VS Variable Speed VSS Vehicle Speed Sensor