How to Test the Crank Sensor on a 4.3 Chevy

by Don Bowman

If a 4.3 Chevy experiences a crankshaft sensor failure, the computer will sense the lack of a signal and set a code describing the failure. In response to the code, the check engine light will illuminate on the dash. On modern vehicles it is difficult to diagnose many items with basic instruments, including this one. The only thing that a volt/ohmmeter can diagnose is a complete failure because the signals are transmitted so rapidly that this type of meter has no way of displaying real time information that a person can see or analyze.

1

Check for a check engine light on the dash. If the light is illuminated, pull the code to determine the failure recognized by the computer by plugging the code scanner to the onboard diagsnostics port under the left side of the steering wheel. Turn the ignition key on. Press the button on the scanner marked "Read." The scanner will display a five-digit code. Cross-reference the code with the code sheet that accompanies the code scanner. If the crankshaft sensor has failed or become irregular, it will say "Crankshaft sensor signal out of range," or "Crankshaft sensor failure."

2

Erase the code and turn the check engine light off by turning the key on and pressing the button marked "Erase."

3

Check the crankshaft sensor for an out-of-range or irregular signal by connecting the computer scanner to the electrical plug on the sensor. Place the scanner in the right mode by inserting the year, make and engine size into the computer. Rotate the knob down to "Crankshaft sensor." Press "OK." Underline the signal integrity graph test and press "OK." There are three wires in the connector. One of the outside terminals is the battery voltage, the center terminal is the PCM, and the opposite side is the sensor signal. Place the red lead on the sensor signal and the black lead to a good ground.

4

Start the engine and watch the graph. There should be squared-off spikes shaped like buildings. They should all be equal heights and evenly spaced. Look for intermittent irregularities or drop-outs indicative of a failing sensor. Rotate the computer knob until it underlines frequency and press "OK." Watch the average frequency and duty cycle. Compare it with the displayed data at the bottom of the screen. The data shows the correct and usable amount of deviation. If the real-time parameters are other than indicated as usable, a failure is imminent.

5

Check the crankshaft sensor for a no-signal situation with the scanner or the volt/ohmmeter. Pull the electrical connector off the sensor. Turn the ignition switch on and test the connector for battery voltage. If no voltage is present, the problem is wiring. If the voltage is present, reconnect the plug. With the key still on, check the center wire with the engine off. The reading on the voltmeter should be less than 100mv. If it reads other than this, replace the sensor.

Items you will need

About the Author

Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).

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