The purpose of this test is to examine the voltage output signal from a Hall Effect crank position (CKP) sensor with the engine running.
This known good waveform has the following characteristics:
The Crankshaft Position (CKP) sensor provides an Engine Control Module (ECM) with its primary timing reference signal. The ECM uses it to calculate the engine speed and position for accurate injection control etc. The signal is also used to detect engine speed anomalies from misfires etc.
Unsurprisingly, Hall effect CKP sensors use the Hall effect, which produces a potential difference (known as the Hall voltage) across the width of a conductor, when it has a current flowing through its length and a magnetic field is applied perpendicular to the current (i.e. through the bottom-top direction of the conductor). When the current is fixed, the greater the magnetic field strength, the greater the Hall effect voltage.
The sensors have in-built conditioning circuits that convert the Hall effect voltage to a stable digital signal output switching between 0 V and 5 V. As they consume power, Hall effect CKP sensors require voltage feed and earth circuits.
The sensor is accompanied by a pulse wheel, typically consisting of 36 or 60 teeth and arranged about the flywheel circumference. As the pulse wheel rotates, each tooth passes through and disturbs the sensor’s magnetic field, which modulate the Hall voltage. In response, the digital sensor output switches either from low to high (0 V to 5 V) or high to low (5 V to 0 V), depending on the sensor circuitry. Therefore, the sensor output is a square wave with its switching frequency dependent on the crankshaft speed.
The pulse wheels have one or more two teeth gaps which indicate specific crankshaft positions to the ECM. These are often mistaken as TDC or BDC indicators.
The CKP sensor signal is critical to ECM operation and failures can cause symptoms such as:
Related failures are:
Selection of component related Diagnostic Trouble Codes (DTCs)
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