Speedo sensors - how do they fail?

It's for my CBR but I think it works on the same principle as the SV...albeit off the gearbox and not off the wheel (which I think the SV runs off?). It's a magnet I think, that detects pulses from a magnet in the gearbox.

So the problem is I have been suffering from an erratic speedo, it keeps reading 0mph at random moments & has been getting worse (more common).

I have got the speedo sensor out now & I can do a test (put it back in, turn wheel, check voltage coming from the sensor - I have the readings it should show).

However given the randomness of the problem (sometimes it will work fine for a whole ride, other times it will be reading 0mph 50% of the time), and the difficulty of getting to the sensor (fuel tank, air box, throttle bodies, coolant reserve tank all off) I want to be 100% sure the sensor is OK before I put it all back together.

So, in what way do these sensors fail? Will I be able to tell (perhaps from the voltage reading) whether it's on the blink & I should replace before putting the bike back together? I would replace it as a matter of principle other than the fact it seems to be £120 for the part

[TSM]

Well its prolly not a magnet in this case, just the sensor sits a couple of mm away from the gear teeth or a special cut pulse rotor and as they pass the sensor it generates enough change in the magnetic field in the sensor for it to be picked up. (or somthin along thoes lines)

To test it off the bike you need to apply voltage to a certain two wires and then mesure the voltage on the third wire and ground, usualy i very quickly move it backward/forwards across a peice of metal like a screwdriver.

how are the connection blocks, corrosion, check all the way to the clocks.

the SV ones tend to fail when people put the front wheel on badly and brake the speedo rotor.

Originally Posted by TSM

Well its prolly not a magnet in this case, just the sensor sits a couple of mm away from the gear teeth or a special cut pulse rotor and as they pass the sensor it generates enough change in the magnetic field in the sensor for it to be picked up. (or somthin along thoes lines)

To test it off the bike you need to apply voltage to a certain two wires and then mesure the voltage on the third wire and ground, usualy i very quickly move it backward/forwards across a peice of metal like a screwdriver.

how are the connection blocks, corrosion, check all the way to the clocks.

the SV ones tend to fail when people put the front wheel on badly and brake the speedo rotor.

The test is done without power to the sensor (it's done unplugged) so would that not indicate it is a magnet? No matter...that test you have would just be easier to do it's basically what is done on the bike anyway.

First step is to buy a multimeter lol - I've got away for this long without one!

I'll be checking the connections as I put it back together, to make sure.

[TSM]

Originally Posted by muffles

The test is done without power to the sensor (it's done unplugged) so would that not indicate it is a magnet? No matter...that test you have would just be easier to do it's basically what is done on the bike anyway.

First step is to buy a multimeter lol - I've got away for this long without one!

I'll be checking the connections as I put it back together, to make sure.

how many wires does the sensor have?

Originally Posted by TSM

how many wires does the sensor have?

I think it has 3 - but it's all in 1 multi-plug. The test described in the service manual (I have a copy of the Honda one) says to unplug that and stick the multimeter in the plug (which means it can't be plugged in to anything else) - I can double check if that really makes no sense though!

[yorkie_chris]

Other things can cause clocks issues, is it charging properly? Have you got a bad earth to the clocks? Corroded connection to the clocks?

i had something similar on my pointy. i thought it was battery, but it was a speedo sensor on the front forks/wheel, it has to be on the 'non-drive' wheel as wheel spins etc would give a false reading.. cost pennies to fix...

Originally Posted by yorkie_chris

Other things can cause clocks issues, is it charging properly? Have you got a bad earth to the clocks? Corroded connection to the clocks?

Yeah all the charging, etc is fine - the part of the harness that is solely the speedo sensor is very small (it's just the wire from the sensor actually) and since nothing else is failing I assume the harness connections from that point on are good - bad assumption?

Originally Posted by richie95

i had something similar on my pointy. i thought it was battery, but it was a speedo sensor on the front forks/wheel, it has to be on the 'non-drive' wheel as wheel spins etc would give a false reading.. cost pennies to fix...

Was your sensor actually failing then? Needed replacement of the sensor right? And was it working intermittently as mine is?

I had a similar issue with my Falco, fortunatly mine was cheap to reaplace (£15 oh baby) and that fixed it. I suspect it was from water ingress.

Dont suppose you know someone with the same bike who is local so you can steel it and test that way?

Originally Posted by ThEGr33k

I had a similar issue with my Falco, fortunatly mine was cheap to reaplace (£15 oh baby) and that fixed it. I suspect it was from water ingress.

Dont suppose you know someone with the same bike who is local so you can steel it and test that way?

No-one local really, but there's a couple of probs with that:

1. My sensor might read the correct values, but only intermittently - so it would 'appear' the same as a good sensor (btw, I haven't tested it yet, but I have a multimeter now - that'll be tonight's job, to check it sends out 0-5V correctly )
2. To get the sensor out is a huge job, if I'm honest - and I don't fancy going through that on someone else's bike (and I don't think they'd appreciate it either!)

I'll test the sensor tonight, but I'll check with a breaker (plenty of bikes on Ebay being broken) about the price for a sensor. Gotta be better than £120!! (and I am shocked by that price, it is a tiny little thing, I can't understand why it seems to be so much more expensive than the sensor on every other bike)