Thank you. It was my cats' fault. I had them in the house overnight because it was so cold. I put them out in the morning, fed and watered 'em, and even treated them to some ice cream, and was only out of the house less than five minutes. Came back in to find a fire in front of the fireplace. Either a log rolled out, which I doubt, or a spark jumped out. At any rate, I hope to back living there within a year.
Those voltages are acceptable. If I were to get picky, you should have 0.2 on the ground wire instead of 0.0 volts, but for diagnostic purposes, if there was a break in the ground circuit, you'd have 5.0 volts on it AND on the signal wire.
0.6 volts on the signal wire is perfect. Typically, anything outside 0.5 to 4.5 volts will set a fault code. This one voltage reading tells us the sensor is okay. You can only have this 0.6 volts if the 5.0 volt feed and 0.0 volt ground circuits, and the sensor itself are okay.
That only leaves two things that can set the fault code. There is a break in the signal wire between the sensor and computer, or there's an intermittent connection in the connector terminals. The easiest way to find that is with a scanner to view live sensor data, but you can do that too with a voltmeter by carefully back-probing the wire at the computer's connector. With a break in the signal wire, you'll have your normal 0.6 volts at idle at the sensor, but you'll find 5.0 volts at the computer, and displayed on the scanner.
There's a "pull-up" resistor in the computer for each sensors' signal wire. It is so big electrically that it has no effect on the circuit when that circuit is working properly, but when the signal wire is broken, the voltage seen by the computer could "float" to some random value due to being connected to the rest of the internal circuitry. The computer could try to run on those erroneous values. The pull-up resistor places 5.0 volts on the signal wire, (only when there's a break in that wire to the sensor), to force it to go to an unacceptable condition and set a fault code.
Since you have a scanner, select the screen that shows sensor data and watch the reading for the TPS. If it's 5.0 volts, look for a break in the signal wire. If it's 0.6 volts, wiggle the connector at the TPS and the wiring harness to see if the voltage changes. If it stays solid, there's one more thing that can cause this code. That's an intermittent contact on the sliding contact inside the sensor. That has the same result as a break in the signal wire and will allow the pull-up resistor to put 5.0 volts on that wire. You'd identify that by slowly running the throttle between idle and wide-open-throttle, by hand. Be aware that all scanner displays respond painfully slowly when looking for this type of intermittent problem, so work the throttle very slowly. Digital voltmeters also respond very slowly. The Engine Computer can detect the slightest momentary blip to 5.0 volts, and set the fault code. Since it's much more sensitive and responsive, if the code sets again while you're working the throttle, replace the sensor, even if you don't see that change on the scanner or voltmeter.
If you do want to replace that sensor, they actually have a pretty low failure rate, so I'd be comfortable with a good used one from a salvage yard.
Saturday, March 22nd, 2014 AT 11:21 AM