You're smarter than most people to ask about the throttle position sensor. WAY too many people would just throw a new one on and expect it to be fixed. In reality, codes never say to replace parts; they only indicate the circuit or system that needs further diagnosis. That said, it's true that the sensor is the problem about half of the time.
You can test the TPS with a digital voltmeter but the glitch you're looking for can occur much quicker than what a meter can detect. Since you already have a scanner, you can read the same TPS voltage on the sensor menu, but here again any dropouts in signal voltage can occur too quickly for you to see. The Engine Computer WILL detect those though and set the code.
You CAN read a hard fault with a voltmeter. The TPS is fed with 5.0 volts on one wire. The ground return wire will have about 0.2 volts. You're interested in the signal wire. There are mechanical stops that only allow it to go from 0.5 to 4.5 volts from idle to wide-open-throttle. If you find 0.7 to 3.8 volts, that's okay too. The point is it sets a code when it goes to 0.0 volts or 5.0 volts. That can only happen with a broken wire or a broken contact inside the sensor.
If you find the signal voltage sweeping smoothly from low to high, the 5.0 volt feed and ground wires have to be okay.
The advantage to reading sensor voltages with a scanner is that you'll see what the computer sees. If you use a voltmeter you might find a nice 0.5 to 4.5 volts at the sensor's signal terminal, but if that wire is broken before it gets to the computer, or if there's a poor connection in the computer's plug, there is a very weak circuit called a "pull-up" circuit to apply 5.0 volts internally to force the computer to set a code. Without that pull-up circuit and with a broken signal wire, the voltage could "float" to some random value due to other circuitry in the computer and that random voltage could be an acceptable value that the computer would try to run on. Because of that pull-up circuit, very often you will see 5.0 volts for the TPS voltage when you unplug the sensor. Some car models do the same thing with a "pull-down" circuit to insure the voltage goes to 0.0 volts when there's a defect.
Wednesday, June 20th, 2012 AT 9:48 PM