That yellow wire is the signal wire for the mass air flow sensor. Where are you measuring it for continuity? That should be at the sensor itself and at the Engine Computer, terminal 31. The best way to verify that wire has a break is to turn the ignition switch on, then measure the voltage on that wire at the sensor. Do that by back-probing through the connector, but it has to be plugged in to be valid. Next, use a scanner to view live data and see what the Engine Computer is seeing for "MAF volts". That has to agree with the voltage you measured at the sensor. If it is different, that wire is indeed open.
Another way to check this is to view the MAF volts on the scanner, then see if it changes when you unplug the sensor. If the voltage jumps up to 5.0 volts or 12 volts, the wire is okay and the sensor is the better suspect.
When there is a break in a sensor's signal wire, since there is so much inter-connected circuitry inside the computer, the voltage on that line will "float" to some random value. If that value stays within the acceptable range, the computer will accept it and try to run on it. That would be extremely difficult to diagnose. To prevent that, all sensor circuits include a "pull-up" or a "pull-down" resistor inside the computer. The pull-up resistor is used most often. That is connected between the computer's internal 5.0-volt power supply and the sensor's signal wire. Under normal conditions, that resistor is so extremely high in value that it is like it isn't even there. It has no affect on circuit operation. It's when the signal wire is broken that the resistor puts 5.0 volts on that signal wire to force a defective condition to be detected, and a fault code to be set.
When a pull-down resistor is used, it is between the signal wire and ground. When the signal wire is broken, it puts 0.0 volts on it to again, force a defective condition. The acceptable range for the majority of these sensors is roughly 0.5 volt to 4.5 volts. It's the voltages outside that range that get detected as defective conditions and set fault codes.
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Thursday, December 27th, 2018 AT 5:42 PM
