23 - Intake air temp sensor out of range, low
Don't even waste your time suspecting this sensor is bad. It only has one component inside, a "thermistor", or temperature-dependent resistor. I tried to install a "bug" into a donated car for my students to diagnose, and there's nothing that can be done to make it cause a problem other than to cut one of its two wires. Doing so, either inside the sensor or in the wiring harness going to it, will cause code 25 to set:
25 - Air temp sensor out of range, high
And you'll notice neither code says to replace it. To get a "low voltage" code 23, the two wires have to be shorted together, or the signal wire has to be shorted to ground. The things to look for are excessive corrosion between the sensor's two pins in its connector, or its signal wire has rubbed through somewhere and is touching a bare metal part of the body or a bracket on the engine. You can verify the sensor is okay by measuring its resistance. Most will read somewhere in the area of 500 to perhaps 10,000 ohms. The resistance will go down as the temperature goes up. Basically all you care about is it doesn't read 0 ohms or open circuit.
A mechanic's next step would be to connect his scanner to view live data and see the voltage on the sensor. It is fed with 5.0 volts, then the sensor draws that voltage down based on temperature. The acceptable signal voltage range is between 0.5 and 4.5 volts. As long as it stays within approximately that range, no fault code will be set.
The next step is to measure the signal voltage at the sensor, (with it still plugged in), and compare that to the scanner's reading. If they're different, suspect a cut wire.
Monday, March 23rd, 2015 AT 2:42 PM