Camshaft position sensor - Hall effect

You will require a PicoScope to perform this test. A list of suitable accessories can be found at the bottom of this page.

The pick-up ring referenced below, relates to a number of possible components such as: Camshaft (teeth, lugs or drillings), timing, or adaptor plate.

The purpose of this test is to evaluate the operation of a Hall Effect Camshaft position (CMP) sensor with the engine at idle speed.

The correct operation of the Hall Effect CMP is dependent upon the integrity of the CMP circuit (power, ground and signal wiring) the fitment of the CMP in relation to the pick-up, the air gap between the CMP and pick-up, and the correct installation and orientation of the Camshaft or pick-up ring. N.B the Camshaft or pick-up ring should also be inspected for damaged teeth and excessive run-out.

The test procedure below assumes the conditions mentioned above are all in order and the CMP to be functioning correctly. Any failures identified with the operation of the CMP whilst conducting these tests does not necessarily indicate a fault with the CMP itself.

The CMP will display operational characteristics that are inconsistent due to circuit faults, electromagnetic interference, mechanical failures or measurement and connection errors. The results obtained are therefore symptoms of underlying conditions and not as a result of a faulty CMP. 

It is therefore paramount to carry out a basic inspection of all the items above before measurements are taken to prevent incorrect diagnosis of the CMP.  All numerical readings quoted in this help topic are typical and not applicable to all engine types.

How to perform the test

Accessories

  • TA125 Premium test lead
  • TA158 Black battery clip
  • PQ070 or PP943 Universal breakout lead set (required size may vary).
PicoScope settings:

Channel A

  • DC coupled
  • Input range: ± 20 V (alternative setting of ± 10 V for CMP with 5 V output signal)
  • Time base 20 ms/div (alternative setting 50 ms/div for additional camshaft rotations)
  • Sample count 1 MS
   

How to connect PicoScope

Using vehicle wiring diagrams, identify the signal wire of the CMP.

The Hall Effect CMP will generally utilise three wires, one of which carries the signal during engine running whilst the others carry a 5 V or 12 V power supply and a 0 V ground reference.

  1. Locate and disconnect the CMP multiplug.
  2. Insert three relevant universal breakout leads between the CMP and vehicle harness in order to complete the circuit.
  3. Connect the blue TA125 test lead to Channel A of the scope
  4. Connect the blue test lead to the breakout lead connected to the signal wire of the CMP (refer to manufacturer  wiring diagram).
  5. Connect the black ground lead to the vehicle chassis or  battery negative terminal using the black TA158 battery clip
  6. Run your scope software by pressing either the spacebar on your keyboard or the Go button in PicoScope.
  7. Crank and run the engine while monitoring the signal on Channel A
  8. Press the Go/Stop button in PicoScope to halt the capture to enable waveform analysis (see Example waveform below).

Example waveforms

All values included in the Example waveform are typical and not specific to all vehicle types.

Channel A. Example waveform indicates the voltage signal (square waveform) output of the CMP with the engine running at idle speed.

NB. The output signal from the Hall Effect CMP can be either 5 V or 12 V depending on manufacturer.

Waveform notes

Typical values

Engine at idle speed (650-850 rpm)

  1. Signal ruler at zero volts indicating the ground level of the CMP output signal.
  2. Indicates the peak voltage  from the CMP sensor (5 V in the example above)
  3. Time Rulers: The Time Ruler handle is located at the bottom left hand corner of the waveform. Drag both Time Rulers to align with specific areas of interest within the waveform. The frequency of the signal between the Time Rulers is recorded in the Frequency Legend (5)
  4. Example waveform 1. Time Rulers highlighting one revolution of the camshaft which will rotate at half engine speed. The Frequency Legend (5) will indicate approximately half engine speed when the Time Rulers are positioned such as to indicate one complete camshaft revolution.
    Example waveform 2. (50 ms/div) Timer Rulers highlighting two camshaft revolutions. Given the camshaft is rotating at half engine speed, in order to establish the repeated pattern obtained from the camshaft pick up (and so qualify one camshaft revolution) the time base has been increased. Here we can identify the unique signal for the camshaft under test as each manufacturer will utilize various pick-ups generating different waveform patterns. What we can be assured of is the pattern will be repeated for every camshaft revolution, hence simplifying identification of a single camshaft revolution
  5. The Frequency /RPM legend indicates the frequency of the camshaft signal based upon the position of the time rulers (3). With the Time rulers placed such as to identify one camshaft revolution, PicoScope will calculate the frequency of 1 full camshaft cycle and display this value in the Frequency Legend (5) In addition, the rpm of the camshaft will also be displayed which equates to half engine speed.
  6. The Ruler Legend recording the numerical time and voltage values relative to the position of the Signal (1) and Time Rulers (3)

Diagnosis

Refer to vehicle technical data for specific test conditions and results.

The example waveform illustrates the square wave 5 V output signal from a Hall Effect CMP. An alternative output signal voltage of 12 V is also used across all manufacturers and so it is vital to check the relevant technical data to ensure the output voltage level is correct. Both styles of CMP will share a common ground level voltage of 0 V as indicated by the Signal Ruler (1) where the numerical value is represented in the Ruler Legend (6). N.B. There maybe occasions where the vehicle manufacturer raises the ground level of the Hall Effect CMP slightly above zero volts in order to reduce noise and improve self diagnosis. (refer to the vehicle technical data).

Unlike the inductive style CMP the amplitude of the Hall Effect CMP signal remains fixed (regardless of engine speed), however the frequency of the signal will increase in direct proportion to engine speed. The correct formation of the square wave signal is paramount to ensure efficent engine performance. Each square pulse is generated by the movement of the camshaft pick-up passing the sensing tip of CMP. Each pulse represents a single tooth, lug or drilling of the pick up which should therefore be uniform in structure, without deformation and identical in sequence.

Depending on manufacturer, numerous style pick-ups are utilised to denote one complete camshaft revolution. In the example wavefroms above three different pulse widths are used per camshaft revoution where other maufacturers may use one single pulse (a single lug) or multiple pulses denoting the precise camshaft postion in relation to firing order (refer to the vehicle technical data).

Technical information

The CMP must be considered an essential component of the modern day engine management system. While compact in construction, the correct operation of the CMP is paramount to an efficient running engine. To fully appreciate the role played by the Hall Effect CMP we must understand the operational principle behind the square wave voltage signal generated by such a critical component. Once we understand how this component functions, we can evaluate the cause of any errors within our waveform.

The Hall Effect principle relies upon a tiny voltage that is generated perpendicular to current flow through a conductor (Hall Element) in close proximity to a magnetic field. If either the current flow or magnetic field changes, the tiny voltage generated will change in direct proportion. The tiny voltage generated across the Hall Element will eventually be amplified and converted into the square wave signal voltage captured in the Example Waveform above

The Hall Effect Element is housed in the sensing tip of the CMP adjacent to a permannet magnet and in close proximity to the camshaft pick up. The rotation of the pick up will change the surrounding magnet field which in turn effects the tiny voltage generated across the Hall Element. The fluctuating tiny voltage is then amplified and converted as mentioned below.

Fundamental to the correct operation of the Hall Effect CMP is the power supply and ground reference at the sensor. A typical CMP sensor connector consists of 3 wires, which can be memorised as “G.P.S” Ground (0 V) – Power (5 or 12 V) - Signal (5 or 12 V)

Both the power and ground are required to supply the integrated circuitry (IC) within the CMP which in turn is responsible for supplying stable current through the Hall Effect Element and converting the tiny voltage generated by the rotating pick up into a stable square wave output signal. 

AT061-4

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.

Suitable accessories

  • PicoScope Battery Clip

    £2.75

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

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Guided test: Camshaft sensor - hall effect