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Coming To You From MotorCity/3071

There are a number of sensors that communicates with the Power train Control Module (PCM) (computer) on the automobiles of today and the one we want to look at for now is the TPS Sensor.Throttle Position Sensor. A throttle position sensor does just what it name implies, Tells the ECM where the position of the throttle is. A TPS is a veritable resistor (potentiometer) it signal input to the PCM is used to calculate engine load, ignition timing, EGR control, idle control and other controlled parameters. A bad TPS can cause hesitation, idle, hard starting and even a no start is possible with a shorted TPS. it can cause a number of driveability problems and may cause the automobile to fail I/M emission test. The three wires of the TPS Sensor, are supplied with a 5 volt via the PCM's VRef circuit, another wire is the sensors ground, and the third wire is the signal output to the PCM.There is a specification for the operating range of the TPS Sensor, Some of the earlier models were adjustable but most of the newer TPS sensors are preset and meet the specifications of the engine. Check the manufacture's specifications for the exact voltage range specification's, but generally the it is from just under one volt at base idle to just under 5 volts at wide open throttle. The TPS can be tested a number of ways: 1. The use of a DMM. 2. A DSO. 3. A Scanner. The vehicle must be on base idle to check the specifications. A sweep test can be made with anyone of the above testers. There should be a constant upscale reading to wide open throttle then a constant down scale reading without any dropouts. The DSO (Lab Scope) is best for this test and the scanner is the lease desired, because of the slow speed, of the measurement. it may miss some glitches or dropouts. The carbon track will most likely wear with in 1/4 of the throttle movement or at the cruise or light throttle position. The PCM does not know how to use a glitch or dropout. lets say the driver of the vehicle is accelerating at a rapid speed and the signal drops out for 2 ms the PCM is told that the driver just released the accelerator and cut the fuel back so now what is happening, the car is stumbling or missing because of a very lean mixture. By -Carlis Wilson 

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My Bio. In the early years, I began working in dealerships as a line technician. I have worked for and trained in Ford, GM, Chrysler, American Motors and a National Transmission Shop. I enjoy Underhood, Driveability Diagnostics, and have earned certifications with Automotive Service Excellence (ASE) and IMACA in Air Condition. ASE Certifications in: Engine Repair, Electrical/Electronic Systems, Engine Performance, Brake Systems, Automatic Trans/Transaxle, Manual Drive Train and Axles. "Tech Tips" has been published in one of the leading Automotive Magazines. A number of other certificates: Doctor of Motors, and Driveablity Related with LTS, NAPA, Motorcraft,  Auto Pro Tech. and others. I have the honor of serving on The Muncie, Indiana State IVY Tech Collage, Automotive Advisory Committee. 

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If you have comments or suggestions, email me at [email protected]

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