Crankshaft position sensor (Hall effect) - running

The purpose of this test is to examine the voltage output signal from a Hall Effect crank position (CKP) sensor with the engine running.

How to perform the test

View connection guidance notes.

1. Use manufacturer’s data to identify the crankshaft sensor signal circuit.
2. Connect PicoScope Channel A to the circuit.
3. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
4. Start the scope to see live data.
5. Start the engine and run at idle.
6. With your waveform on screen stop the scope.
7. Turn off the engine.
8. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

• A digital signal switching from a low voltage, just above 0 V, to a high voltage, just below 5 V.
• Clean transitions between the two, stable, voltage levels.
• No excessive hash or intermittent signal dropouts.
• A switching frequency that increases with increasing engine speed.
• A periodic decrease in the switching frequency, causing it to appear almost halved. These events are every 180° degrees of crankshaft rotation in this example.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select Crankshaft sensor (Hall effect)

Further guidance

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:

• Engine cranking but not starting
• Engine cutting out
• Malfunction Indicator Lamp (MIL) illumination
• Diagnostic Trouble Codes (DTCs)

Related failures are:

• Short or open circuits or high circuit resistances.
• Internal sensor circuit failures.
• Signal errors resulting from excessive dirt or detritus on the sensor housing or pulse wheel.
• Incorrect fitment or operation of the sensor or crankshaft components, causing:
  • Excessive gaps between the sensor and the pulse wheel.
  • Damage to the sensor housing or pulse wheel.
  • Excessive crank or flywheel movement or vibration.

GT012