Neutral switch

Figure 1

Figure 2

How to perform the test

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) neutral switch 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.

Hit the space bar to start capturing live readings.

With the motorcycle on the centre or side stand, operate the gear lever up and down with the ignition turned on.

Example waveform

Waveform notes

As the gear lever is moved between neutral and a gear selection, the voltage in this instance can be seen to rise from approximately 0.6 volts (in the neutral position) to 4.7 volts. The voltage change shows that the switch is working correctly and that the correct safety-related information is being sent to the motorcycle's ECM. The voltage range may have to be adjusted to accommodate some motorcycle manufacturers as they could use the 12 volts provided by the battery. The timescale used is not as important as in other testing applications but can be adjusted to suit the vehicle. The trigger on the oscilloscope is set to none, as there is no recurring signal to trigger from.

Technical information

Motorcycle manufacturers employ a neutral switch to supply information to the rider to inform them when neutral has been selected. With a gear lever that only moves up and down, neutral selection is not as obvious as when driving a car. The neutral switch also performs an important safety function when working along with the side-stand switch. If a gear is selected while the side-stand is down, the engine's ignition and fuelling are automatically cut.

This avoids the rider moving off with the side-stand down, which could cause the forward facing stand to dig into the road as the machine is leant over into a corner. The neutral switch is located into the gearbox and looks like a reversing light switch used on a car.

If the switch fails, this will result in failure of the neutral light to illuminate and the engine to continue to run when a gear is selected while the side-stand is down. There will be no voltage change in the oscilloscope waveform and the fault should be rectified as soon as possible as it has serious safety implications.

Pin data

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

AT120-2