The way they had you do the test for the ground circuit is kind of odd. It will work, but you have to add in the variable of battery voltage. A good, fully-charged battery will read 12.6 volts, but if it has been freshly charged, it is going to have some "surface charge"; that's free electrons in the electrolyte that haven't been absorbed into the plates yet. Surface charge can produce a false battery voltage reading that's too high, often as high as 13.0 volts.
Suppose you start with that 13.0 volts, then you find 12.4 on the TPS ground terminal. That means there's actually 0.6 volts, (in reference to ground), on that terminal, which is not acceptable. That circuit should have 0.2 volts.
If you have 12.6 volts on the battery, meaning any surface charge has been removed, and you find 12.4 volts, as before, on the TPS ground terminal, you now have 0.2 volts on that ground circuit, which is perfect. This might sound like I'm picking nits, but in such a low-current circuit like this ground circuit, to have that extra 0.4 volts indicates there's a serious high-resistance problem in it. That is not enough to trigger fault codes for any of the sensors that share that ground circuit, but it will sure cause some weird and elusive driveabilty issues. In particular, the MAP sensor uses that ground circuit. It has the biggest say, (only on Chrysler products), in the fuel metering calculations. A tenth of a volt error can cause hesitations, stumbling, poor fuel mileage, and other miserable problems, all with no fault code to direct you to the cause.
I also didn't like their comment about it being okay to take the readings with the sensor unplugged. Remember my comment about the compressed air line in the shop that is 99 percent blocked? If you start with 100 psi at the compressor, you'll have 100 psi at the end of your hose, as long as you're not trying to run an air tool. As soon as you turn on the tool, almost no air volume can get through, and pressure after that blockage will be near 0 psi. You need to cause air to want to flow by turning on the tool, then, if you take multiple pressure readings, you'll find 100 psi all the way up to the blockage, and 0 psi after the blockage. Those pressure readings are what you'll use to find the location of the blockage, (high resistance to air flow).
Electrical circuits work exactly the same way. Electrical pressure is voltage, and flow, or volume, is current. Please forgive me if this gets too technical, but suppose there is corrosion in a splice that's coming apart in the 5.0-volt feed circuit. That's the blockage equivalent in the air line, and we'll say it's 5,000 ohms. The exact resistance of any throttle position sensor is irrelevant, but a typical value is also 5,000 ohms. With the sensor plugged in, current will flow equally through that corroded splice, the sensor, and the wires. Half of the 5.0 volts will be "dropped", or used up, across the sensor and half will be dropped across the undesirable resistance in the splice. You started with 5.0 volts at the computer, lost 2.5 volts across the corroded splice, so you end up with the other 2.5 volts at the sensor. That means you'll measure 2.5 volts at the 5.0-volt feed terminal at the sensor, and that will instantly tell you there's something wrong in that circuit. If you were to measure the voltage with the sensor unplugged, as they suggested, no current would flow through that circuit, so none of the 5.0 volts would be dropped across the high-resistance splice. That leaves you with the entire 5.0 volts at the sensor, which would falsely tell you the circuit is okay.
By telling you it's okay to take the voltage readings with the sensor unplugged, it is the same as saying you have 100 psi at the end of the air hose, so the pipes have to be okay. Neither test this way takes into account the blockage or high resistance.
As a side note, this is why I often recommend using a test light instead of a digital voltmeter, in most circuits. The voltmeter just takes a pressure reading. The test light requires current to flow through it to work, and it will show up as a dim light when there's too much undesirable resistance in the circuit.
Regardless, in your original post, you were way ahead by testing the signal voltage. As I mentioned, the only way you can get the correct sweep from 0.5 to 4.5 volts that you found is if the 5.0-volt feed and ground circuits are okay. The time to move backward and do the individual tests on the other site is when the signal voltage does not go through the proper sweep, then you have to use those individual tests to figure out if the defect is in the 5.0-volt feed circuit or the ground circuit. Since we're past that, the only thing left is the signal wire running back to the computer. Unless I overlooked something, there's only two things that can happen to cause the TPS fault code to set. There has to be a break in the signal wire, in which case the reading you get at the sensor will not agree with what the computer is seeing, (this is where you need the scanner to see that data), or there is an intermittent dropout in the signal voltage. That glitch only has to last a tiny fraction of a second to be detected by the computer. It could be caused by a speck of dirt getting caught under the wiper / movable contact inside the sensor. That would create an open circuit, then the pull-up resistor would place 5.0 volts on the signal circuit that would be detected as outside the acceptable range of 0.5 to 4.5 volts. That doesn't happen very often. Even less common would be a loose rivet that connects the metal terminal to the carbon strip inside the sensor. If that loose connection was on the ground terminal, that too would send the signal voltage to 5.0 volts momentarily. If the rivet, or the connector terminal for the 5.0-volt supply had an intermittent connection, the loss of the 5.0 volts would send the signal voltage to 0.2 volts, also detected as a defective condition.
Now we're back to observing when the fault code sets. If you erase it, and it comes back instantly, that's the easiest to find because the defect is there all the time. As with the pressure tests on the compressed air pipe, a couple of voltage readings will locate the break in the signal circuit. It's the defects that don't show up for hours or days that are the most frustrating. Often they will show up from wiggling wiring harnesses and putting pressure on connectors. The goal here, if possible, is to do something that makes the defect show up, then be careful to try to keep it in that defective state so you can find it with the voltage readings.
Friday, June 19th, 2020 AT 8:06 PM