Engine speed and position sensors

Figure 1

Figure 2

Figure 3

How to perform the test

In this example we have chosen to dual-trace engine speed and camshaft position sensor, but either sensor can be checked on its own if preferred.

Channel A

Plug a BNC test lead into Channel A of the scope. Place a small black clip on the lead end with a black moulding (negative) and a Back-pinning Probe onto the end with a red moulding (positive). Place the small black clip on to the motorcycle frame or battery negative, as illustrated in Figure 1. Check the manufacturer's pin data for the fuel injection Electronic Control Module (ECM) engine speed sensor connection terminal. Back-probe the correct multiplug pin with the Back-pinning Probe as in Figure 2. Ensure that a good connection is made through to the wire or terminal and the probe has pierced through the wire and plug insulation.

Channel B

Plug a BNC test lead into Channel B of the scope. Place a Back-pinning Probe onto the end with a red moulding (positive). Piggyback the black moulded end of the BNC test lead (negative) onto the connection already made to either the motorcycle frame or battery negative, as illustrated in Figure 3. Check the manufacturers pin data for the fuel injection Electronic Control Module (ECM) camshaft position sensor connection terminal. Back-probe the correct multiplug pin with the acupuncture probe as in Figure 2. Ensure that a good connection is made through to the wire or terminal and the probe has pierced through the wire and plug insulation.

With the example waveform displayed on the screen you can now hit the space bar to start looking at live readings.

Note: this waveform was captured just above idle speed. As the engine speed increases so will the AC voltage of both sensors, and this may require some adjustments to the screen settings.

Example waveform

Waveform notes

In this dual-trace waveform we can evaluate the output voltage from the Crank Angle Sensor (CAS) that measures the engine's speed (red trace) and the blue trace that denotes the engine's position. These voltages will differ between different motorcycle manufacturers.

Technical information

Engine speed sensor

This sensor is also known as a Crank Angle Sensor (CAS) or Crankshaft Position Sensor (CPS). The output signal produced is used by the Engine Control Module (ECM).

On an inductive CAS/CPS a resistance value should be seen between the terminals. The inductive sensor is normally a two-wire device, but some manufacturers use three wires, the third being a coaxial braid to keep out any HT interference that may interrupt and corrupt the signal seen by the ECM. Engine speed sensors tend to fail as they become hot and the windings become open-circuit; in this instance the engine will stop but restart if left to cool down.

Camshaft (cylinder) position sensor

The camshaft sensor is sometimes referred to as the Cylinder Identification (CID) sensor or 'phase' sensor and is used as a reference to phase the sequential fuel injection by the Electronic Control Module (ECM). This type of sensor (inductive) generates its own signal and therefore does not require a voltage supply to power it. It is recognisable by its two electrical connections, with the occasional addition of a coaxial shielding wire.

The voltage produced by the camshaft sensor is determined by several factors: the engine's speed, the proximity of the metal rotor to the pick-up and the strength of the magnetic field offered by the sensor. The ECM needs to see the signal when the engine is started for its reference; if this is absent it can alter the point at which the fuel is injected.

The characteristic of a good inductive camshaft sensor waveform is a sine wave that increases in magnitude as the engine speed is increased.

Faulty waveforms - troubleshooting

The output voltage produced on the sensors is manufacturer-specific, with outputs that reduce if the sensors' air gaps are too big. In some cases the air gaps are non-adjustable, while on other engines the air gaps can be adjusted and measured using feeler blades. A larger air gap reduces the voltage output from the sensor.

A failing sensor with shorted windings also reduces the voltage output, while a sensor with an open circuit has no output at all. The condition of the winding inside the crank angle sensor can be determined by a resistance test made with a multimeter.

Pin data

Our test vehicle was a Honda motorbike. Below is the ECM multiplug pin data. Pin data will be manufacturer and model specific and this data is shown for illustration purposes only.

AT104-2