Camshaft sensor - Hall effect

The purpose of this test is to evaluate the operation of a Hall effect Camshaft Position (CMP) sensor from its output voltage.

How to perform the test

View connection guidance notes.

1. Use manufacturer’s data to identify the camshaft sensor output 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 waveforms 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.
• The relative periods between the high and low voltages indicate the phases of the camshaft’s rotation with respect to the cylinder firing order.
• The overall waveform frequency will increase with increasing engine speed.

Waveform Library

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

Further guidance

A CMP sensor signals one or more fixed camshaft reference positions to the Engine Control Module (ECM), for example, the arrival of a cylinder’s intake stroke. The ECM uses the camshaft sensor signal for accurate timing control of ignition (if a gasoline engine), injection, and variable valve phasing, etc.

As their name implies, Hall effect CMP 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 voltage to a stable digital signal output switching between 0 V and 5 V. As they consume power, Hall effect CMP sensors require voltage feed and earth circuits.

The sensors are accompanied by a pulse wheel. As the pulse wheel rotates, it passes through and disturbs the sensor’s magnetic field to 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. The overall frequency of the signal will depend on the camshaft speed.

The pulse wheel can have unique patterns for each cylinder, just a single pulse, or something in between. With unique patterns for each cylinder, the CMP sensor signal can be used in a rapid start process. For example, a 4-cylinder engine can start within 180 degrees of crankshaft rotation (90 degrees of camshaft rotation). In these applications, a CMP sensor may be referred to as a Cylinder Identification (CID) sensor or phase sensor and the pulse wheel may be referred to as a phase wheel.

The CMP sensor signal can be critical to ECM operation and failures can cause symptoms such as:

• Engine cranking but not starting
• Engine cutting out
• Erratic running
• Limp-home mode operation
• Malfunction Indicator Lamp (MIL) illumination
• Diagnostic Trouble Codes (DTCs)

Related failures are:

• Shorts, opens or high resistances in the signal, feed or earth circuits.
• 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.

GT061