Nope. Some cars and some scanners read throttle position as a percentage, but it's much more common to read it as a voltage. On 99 percent of car brands and models the TPS, along with most other sensors, is fed with 5.0 volts. The ground wire would have 0.0 volts but since it goes to ground through monitoring circuitry inside the computer, you'll actually find close to 0.2 volts on it. For purposes of this story, we'll consider that 0.0 volts. If this were a volume control on a radio, you could turn it to vary the signal voltage from 0.0 to 5.0 volts. However, on a throttle position sensor, there are mechanical stops, either inside the sensor or on the throttle body, that limit its travel to roughly 0.5 volts to 4.5 volts. (Your 9.4% would equate to 0.5 volts).
The only way the TPS signal voltage could go all the way down to 0.0 volts is if there was a break in the 5.0 volt feed wire or the connection inside the sensor. The only way it could go to 5.0 volts is if there was a break in the ground wire. Either condition will trigger a diagnostic fault code. It's by those voltages outside the acceptable range of 0.5 to 4.5 volts that the computer identifies when there's a defect.
There's one other condition that will set a fault code. That's a break in the signal wire or that connection inside the sensor. That can allow the signal voltage seen by the computer to "float" to some random value due to being interconnected to all the other circuitry inside the computer. The computer could use those erroneous readings to try to run on, and that would cause all kinds of weird and intermittent symptoms. To prevent that, they always use a "pull-up" resistor or "pull-down" resistor. A pull-up resistor is more common. It is so big electrically that it has no effect on the circuit or its operation, ... Until there's a break in the signal wire. Then, since it is connected to the 5.0 volt internal power supply, it puts 5.0 volts on the signal wire which forces the computer to see the defective condition and set a fault code. If a pull-down resistor was used, it would apply 0.0 volts to the signal wire which would also trigger a fault code.
Every car and every sensor is different. The acceptable range of 0.5 to 4.5 volts is used for training, but you might find one car has a range from 0.42 to 4.45 volts, and an identical model car or a different sensor produces a different range. The computer has to learn when those minimum voltages change, as in when a sensor is replaced. In the case of a TPS, when the computer sees what it knows to be the lowest TPS voltage, it knows your foot is off the accelerator pedal and it has to be in control of idle speed. If you install a new sensor with a minimum voltage even slightly higher than the old one, the engine could stall from the idle speed being too low until the new "minimum throttle" is learned. All manufacturers have a different strategy to cause that relearn to take place. On some you'll never notice a problem. Others simply require certain conditions to be met during a test-drive.
Monday, April 28th, 2014 AT 11:14 AM