How to Test a Crankcase Position Sensor
If your car stalls while driving, surges unpredictably or doesn't start when the engine is warm, you may want to test your crankcase position sensor (CPS) for damage. This isn't that difficult because all vehicles made since 1996 are required to be On-Board-Diagnostic (OBD II) compliant. Pull out a simple plug under your dash, plug into an OBD II scanner, and perform the test.
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Instructions
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Reach under your dash and locate the OBD II transmitter plug. It will look like a narrow receiving plug about 1/2 inch wide and 2 inches long with 16 connections inside it. Pull the plug so it hangs down beneath the dash.
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Connect the transmitter plug to the scanner's receiving connector by pushing the two halves together.
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Turn the scanner on. Set your scanner to read live data on RPMs. Depending on the scanner model, this may appear as a numeric readout or a graph function.
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Press your accelerator pedal to the floor and hold it. Crank the engine over and check the RPM data. If you are registering less than 300 RPMs, your sensor is not working correctly.
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Tips & Warnings
If you don't own an OBD II scanner, you can "borrow" one at your local auto parts supply store. Many of the chain stores offer loaner tools for use in their parking lots. It must be a live-feed scanner so it can perform the RPM test.
Do not force the connection between the OBD II scan device and the transmitter plug. This can damage both parts. If the connection does not go together easily, try it a different way. If it still does not connect easily, chances are you may have an OBD I-compliant vehicle.
