How to Test a Crankshaft Position Sensor?
2 Answers
Crankshaft position sensor testing methods are as follows: 1. Measure the sensor's own resistance using a multimeter in resistance mode to check the resistance value of the crankshaft position sensor itself. However, this method is only applicable to magnetic induction-type crankshaft position sensors. For Hall-effect or photoelectric-type crankshaft position sensors, which often have internal shaping circuits, measuring resistance often makes accurate judgment difficult; 2. Measure signal voltage by using a multimeter in voltage mode to check the output signal voltage of the crankshaft position sensor. However, this test is conducted based on circuit diagrams and signal waveform analysis. When engine speed changes, the peak voltage and frequency of the magnetic induction-type crankshaft position sensor signal will vary. The higher the engine speed, the greater the signal peak voltage and frequency become, and the signal voltage detected by the multimeter will also increase accordingly. For photoelectric and Hall-effect crankshaft position sensors, their signal peak voltage and duty cycle do not change with engine speed variations—only the frequency changes. When using a multimeter to measure their signal voltage, the signal voltage remains constant, which must be noted; 3. Check output waveform by using an oscilloscope to detect the output waveform of the crankshaft position sensor. This method allows for intuitive observation of the sensor's waveform. The output waveform of a magnetic induction-type crankshaft position sensor is generally a sawtooth wave, while photoelectric and Hall-effect types produce square wave outputs.
Checking the crankshaft position sensor is actually quite crucial. I usually start with the engine warning light—if it's on, the first step is always connecting an OBD scanner to read the fault codes. A code like P0335 directly points to a crankshaft sensor issue. Next, I use a multimeter for testing: unplug the sensor connector and measure voltage and resistance across the terminals. If the resistance is abnormally high or low, or there's no 5V signal voltage output during startup, the sensor is likely faulty. I also prefer checking the signal waveform with an oscilloscope to ensure the curve is smooth—excessive fluctuations indicate malfunction. Always remember, the sensor is usually located near the flywheel at the rear of the engine; keep the connector free from oil or dirt buildup—clean it thoroughly before testing for accurate results. If you experience hard starts or engine stuttering, a failed sensor is a prime suspect—replace it promptly to avoid worse failures. A faulty sensor can disrupt ignition timing, making driving unsafe, so address any symptoms immediately. I've seen many vehicles requiring major engine repairs due to this small component, wasting money and causing unnecessary downtime.
