Another speed sensor thread

Seems like a reasonably common issue but the speedo has stopped working on my Monster 796. It was intermittent, now digital gauge sits at 0. I've fallen at the first hurdle and struggling to remove the sensor, any tips for accessing the hex head screw that attaches the sensor. The swing arm gets in the way when lining up an Allen key and I fear I'm rounding off the head. I'll try and upload a picture separately. Thanks!

[Darren69]

Are you sure it is the sensor and not the plug that's faulty?

Have you tried with a ball ended key? A better option may be a hex socket bit with a extension bar in a ratchet driver. I bought a set 40pc bit set recently after snapping the ball end off of one of my allen keys and it has proved very useful over the traditional allen keys.

[mickj]

That does look like an awkward little bugger, you could try a cut down Allen key and /or use a bit of grinding past on the key to give it a bit more purchase.

I did give the plug a wriggle and a squirt of WD40 if that counts as diagnostics!

[Darren69]

Originally Posted by se96djre

I did give the plug a wriggle and a squirt of WD40 if that counts as diagnostics!

Pull the plug apart and clean with electrical contact cleaner. WD40 will clean but it doesn't conduct electricity, it's an insulator so it won't help the ions flow if it's on the plug connectors it certainly won't help matters

[Darren69]

If it's an ampseal plug I'd be surprised if dirt had got in there however, but it's worth a try. I think the only sure fire way to properly diagnose the fault is with a multi-meter to test continuity and resistance across the sensor end of the plug and then maybe continuity across the speedo end of the plug if the sensor plug checks out ok.

[Luddite]

I'm assuming that the 796 uses the same speed sensor as my 1100 Evo, in which case it will be a two-wire unit no. 28 on the wiring diagram.



If you have a multimeter, it's a simple job to check. Place the black meter wire on the black terminal and the red meter wire on the white terminal. Set the meter to AC volts (NOT DC as you might expect because the sensor output is in the form of a sine wave). Spin the rear wheel and, if the sensor is working, you should see a voltage increase on the meter - the faster the wheel, the greater the voltage.

Thanks for the excellent advice chaps. Connectors all looked fine but cleaned with metal cleaner. Tried to get the voltmeter hooked up to the sensor and didn't get any readings. I fear that could well have been down to poor contacts, was struggling to hold the probes in plug and spin wheel. I'm a bit of an amateur!

[Luddite]

A second pair of hands is definitely useful for this! Do you have crocodile clips on your meter leads? Try attaching them to the contacts if you have the room, which will keep your hands free to turn the wheel. (Note - if you're spinning the wheel by hand, you probably won't see much more than 0.5v on the readout.)

Alternatively, if you can attach the meter to the plug securely and the leads are long enough, try resting it on the tank and ride the bike slowly up your drive while checking the meter.

By the way, if you find you need a replacement, the part no. is 55212121B.

[Darren69]

150 euro, ouch.

Remember this one? Ended up asking the garage to do it when it was in for the MOT (I bought a second hand sensor from Italy as the others I could find had a slighty different connector). Ended up being a wheel off job in the garage!

[Luddite]

Good news - well done!