Although conventional throttle position sensors attached to the throttle shaft are considered basic technology on modern engine management systems, the conventional throttle sensor plays an important role in its relationship with other sensors. The voltage inputs of most throttle position (TP) sensors may, for example, be coordinated with the barometric pressure (BARO), manifold absolute pressure (MAP), mass air flow (MAF), engine coolant temperature (ECT), intake air temperature (IAT), crankshaft position (CKP) and vehicle speed (VSS) sensors. From the combined data inputs of these sensors, the OBD I engine control module (ECM) or OBD II powertrain control module (PCM) calculates the correct electrical outputs for actuators like the ignition control module (ICM), fuel injectors, idle speed control and fuel pump.

Of course, throttle sensors don't always produce identical symptoms when they fail because an ECM's or PCM's self-diagnostic strategy can be very application-specific. In addition, not all throttle sensors are identical in design or operation. Consequently, it's important to understand how a TP sensor may control or affect an engine management system.

Early TPS Designs
Many pre-1996 OBD I-equipped vehicles utilize throttle sensors in a much different way than do current OBD II models. For example, many OBD I throttle sensors incorporated a "nose switch" function that would indicate to the ECM when the thr...