What is the problem you're trying to solve?
If you measured the voltage on the signal wire while the TPS was unplugged, you will get either a very high voltage or 0.0 volts. The reading is not valid unless it is taken by back-probing the connector while it is plugged in.
When a sensor is unplugged, it's signal wire is interconnected to all the other circuitry inside the computer, so the voltage seen on that wire can "float" to some random value. The TPS is fed with 5.0 volts and ground, (0.2 volts). The movable contact finds a point along the sensing element corresponding to throttle position, but there are mechanical stops that limit its travel to 0.5 volts to 4.5 volts. Anything outside that range is what triggers a fault code.
When the voltage floats to a random value on an unplugged, (or cut) signal wire, if it remains within the acceptable range, no fault will be detected, and the computer will try to run on that value. To prevent that, every sensor circuit is internally connected to a "pull-up" resistor or a "pull-down" resistor. When the circuit is working properly, that resistor is so high in value, it's like it isn't even there. However, when the signal wire is cut or unplugged, that resistor places 5.0 volts or 0.0 volts on that wire to force it to go to a bad state, then the defect can be detected and a fault code is set.
If you're reading the signal voltage with the sensor unplugged, you're reading the voltage coming through that pull-up resistor. You gotta plug it back in for the reading to be valid.
Thursday, December 29th, 2016 AT 3:42 PM