312 Auto Engine Repair Copyright by Goodheart-Willcox Co., Inc. Idle control valve Manifold absolute pressure sensor Throttle position sensor Intake air temperature sensor EGR valve A/C idle control solenoid valve EGR valve lift sensor Oxygen sensor Engine coolant temperature sensor Crankshaft position sensor Figure 15-10. There are many engine sensors on a modern vehicle. Common sensors are identified here. (Honda) Water shield assembly Heater termination Sensor lead Flat seat shell Seat gasket Outer electrode and protective coating Rod heater Zirconia element Insulator Clip ring Gripper Four wire inline connector Inner electrode Figure 15-11. An oxygen sensor monitors the air-fuel ratio by vary- ing its output based on the amount of oxygen in engine exhaust. designed to help keep the vehicle running efficiently for at least 100,000 miles (160,000 km). On-Board Diagnostics Generation Two (OBD II) A poorly tuned or malfunctioning vehicle is a source of significant air pollution. It can produce several times the normal amount of emissions. For this reason, the California Air Resources Board (CARB) along with the Environmental Protection Agency (EPA) developed regulations that require on-board diagnostic systems to detect problems before they can result in the vehicle producing harmful exhaust emis- sions. These regulations also require vehicle manufacturers to standardize the performance monitoring systems on their cars and light trucks. Today’s on-board diagnostics will check the operation of almost every electrical and electronic part in every major vehicle system. A vehicle’s engine control module can detect engine misfiring and air-fuel mixture problems. It monitors the operation of the fuel injectors, ignition coils, fuel pump, emissions system parts, and other major components that affect vehicle performance and emission control. The on-board computers used in OBD II systems have greater processing speed, more memory, and more complex programming than computers used in OBD I systems. New vehicles now monitor more functions and can warn the driver and technician of more possible problems that affect driveability and emissions. The OBD II diagnostic system can produce over 500 trouble codes related to engine performance. It checks the operating parameters of switches, sensors, actuators,