Crankshaft 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 pickup ring reference below relates to a number of possible components.

 (For example the flywheel, drive plate, pulley assembly, timing plate, adaptor plate or ring gear.)

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

The correct operation of the Hall Effect CKP depends on the integrity of the CKP circuit (power, ground and signal wiring), the placement of the CKP in relation to the pickup, the air gap between the CKP and the pickup, and the correct installation/orientation of the pickup ring.

N.B.: The pickup ring should also be inspected for damaged teeth and excessive run-out.

The test procedure below assumes that the conditions mentioned above are all in order. Any failures identified with the operation of the CKP while conducting this test do not necessarily indicate a fault with the CKP itself.

The CKP will display operational characteristics that are inconsistent due to circuit faults, electromagnetic interference, mechanical failures (pickup ring) or measurement/connection errors. The results obtained can, therefore, be symptoms of underlying conditions and not the result of a faulty CKP.

It is paramount that you carry out a basic inspection of all the items above BEFORE measurements are taken to prevent an incorrect diagnosis of the CKP.

All numerical readings quoted in this help topic are typical and not applicable to all engine types.

How to perform the test

Accessories

PicoScope settings

  • Channel A: ± 20 V DC
  • Timebase: 200 ms/div
  • Number of samples: 1 MS

Use the vehicle wiring diagram to identify the signal wire of the CKP.

The Hall Effect CKP will generally utilize three wires, one of which carries the signal when the engine is running while the others carry a 5 or 12 V power supply and a 0 V ground reference.

  1. Locate and disconnect the CKP multiplug
  2. Insert three relevant universal breakout leads between the CKP and vehicle harness in order to complete the circuit again (see Figure 1)
  3. Connect the blue TA125 test lead to channel A on the scope and to the breakout lead connected to the signal wire of the CKP. (Refer to the manufacturer’s wiring diagram to find the wire.)
  4. Connect the black ground lead to the vehicle chassis or battery negative terminal with the black TA158 battery clip
  5. Run your scope software by pressing either the space bar on your keyboard or the "start" button in PicoScope.
  6. Crank and run the engine whilst monitoring the signal on channel A
  7. Press the start/stop button in PicoScope to halt the capture to enable waveform analysis. (See Example waveform below).

Example waveform

All values included in the example waveform are typical and may not apply to all vehicle types.

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

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

Waveform notes

Typical values

With the engine at idle speed (approximately 650-850 rpm):

  1. A signal ruler at zero volts indicates the ground level of the CKP output signal.
  2. Indicates the missing teeth from the CKP pickup ring, often mistaken for TDC
  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 the missing teeth from the pickup ring, in order to measure the engine speed recorded in the Frequency / RPM Legend (marker 5)
  4. Time rulers highlighting one revolution of the crankshaft between the missing teeth of the pickup ring. The example waveform confirms 58 teeth in one crankshaft revolution with 2 missing teeth denoting crankshaft position (referred to as 60 -2).
  5. The Frequency /RPM legend Indicates the engine speed based on the position of the time rulers (marker 3). Time rulers placed at subsequent missing teeth of the pickup ring allow PicoScope to calculate the frequency of one full cycle (revolution) of the crankshaft. Both the frequency and more importantly, the RPM are then displayed at marker 5.
  6. The Ruler legend recording the numerical time and voltage values relative to the position of the signal (marker 1) and time rulers (marker 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 CKP. An alternative output signal voltage of 12 V is also used across all manufacturers, so it is vital to check the relevant technical data to make sure that the output voltage level is correct. Both styles of CKP will share a common ground level voltage of 0 V as indicated by the signal ruler (marker 1) where the numerical value is represented in the ruler legend (marker 6). Unlike the inductive style CKP, the amplitude of the Hall Effect CKP 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 efficient engine performance. Each square pulse is generated by the movement of the pickup ring teeth passing the sensing tip of CKP. Each pulse represents a single tooth of the pickup ring which should, therefore, be uniform in structure, without deformation and identical in sequence. Depending on the manufacturer, there are generally 36 or 60 teeth on the pickup ring with 2 missing teeth (reference signal) used to denote one complete revolution of the engine and the crankshaft position.

An indication of the amount of crankshaft rotation per pickup ring tooth can be calculated as follows:

Pickup ring with 36 – 2 teeth

One crankshaft rotation = 360 degrees / 36 teeth = 10 degrees

Each tooth equates to 10 degrees of crankshaft rotation.

Pickup ring with 60 – 2 teeth

One crankshaft rotation = 360 degrees / 60 teeth = 6 degrees

Each tooth equates to 6 degrees of crankshaft rotation.

NB. The PCM uses the missing teeth (reference signal) of the CKP signal to identify the position of the crankshaft, which may or may not refer to TDC. Manufacturers will use the missing teeth from the pickup ring to indicate a variety of crankshaft positions. For example Pistons in line, (Engine safe position) TDC, X number of degrees before TDC; or they may choose a combination of missing teeth at 90-degree intervals. For an accurate evaluation of the crankshaft position reference signal, refer to the relevant workshop manual.

Technical information

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

The Hall Effect principle relies upon a tiny voltage that is generated perpendicular to current flow through a conductor (Hall Element) in a magnetic field. If either the current flow or the magnetic field changes, the tiny voltage that is 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 CKP, adjacent to a permanent magnet and close to the pickup ring. The rotation of the pickup ring will change the surrounding magnet field which in turn affects the tiny voltage generated across the Hall Element. The fluctuating tiny voltage is then amplified and converted.

Fundamental to the correct operation of the Hall Effect CKP is the power supply and ground reference at the sensor. A typical CKP sensor connector consists of 3 wires, which can be memorized 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 circuit (IC) within the CKP, which in turn is responsible for supplying stable current through the Hall Effect Element and converting the tiny voltage generated by the rotating pickup ring into a stable square wave output signal.

AT012-4

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

  • Back-pinning Probe Set

    £48.00

  • Flexible Back-pinning Probe

    £4.25

  • PicoScope Battery Clip

    £2.75

  • Large Dolphin/Gator Clips

    £10.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £47.00

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

    £179.00

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Guided test: Crankshaft - Hall Effect