Speedo showing random numbers. Speed sensor seems in one piece?

[Barney626]

Hi all,

Pulled the bike out the garage today after riding without issue yesterday to find the speedo throwing up random numbers from 0 to 186mph. Happens when moving and still, engine off or on.

Tried checking the speed sensor rotor for broken tabs but looks to be totally intact. Tried measuring the pink wire voltage at the white connector and was seemingly normal at 4.5v ish each time it went past a magnet.

Any ideas what else I can look at or whether a new sensor is going to fix this?

Thanks

[Seeker]

The manual says that any voltage over 3.7V is acceptable so if you're getting 4.5V pulses, your sensor is probably ok but there is a resistance check you can do too, on the sensor and from the sensor to ground:
https://www.manualslib.com/manual/80...age=399#manual


I'm guessing there's a couple of connectors between the sensor and the speedo, I'd check them for corrosion - it sounds like your speedo is responding to noise.

[Barney626]

Originally Posted by Seeker

The manual says that any voltage over 3.7V is acceptable so if you're getting 4.5V pulses, your sensor is probably ok but there is a resistance check you can do too, on the sensor and from the sensor to ground:
https://www.manualslib.com/manual/80...age=399#manual


I'm guessing there's a couple of connectors between the sensor and the speedo, I'd check them for corrosion - it sounds like your speedo is responding to noise.

I had a bit more of a fiddle with it and narrowed down the behavior some more.

When I turn the wheel so there isn't a magnet next to the sensor I get 0 volts and the dash stays at 0mph. But when I turn the wheel to a magnet and stop it moving (Hold it by the magnet) I get a slightly fluctuating 4-4.5v and the speedo reads random numbers.

I would have thought if it measured pulses with the wheel totally still it wouldn't be reading a speed so clearly it's the fluctuating voltage coming from somewhere.

I've had a look in my haynes manual at the wiring diagram and as far as I can see there are only 2 connectors between the sensor and the dash. The first is the white plastic 3 pin connector under the tank and the second is the main plug into the dash.

When I disconnect the white connector the dash stops showing random numbers. The white connector seems in decent condition with no corrosion, i've scraped off the pins with some contact cleaner anyway but no improvement.

I've also unplugged the dash connector and that looks to be in pristine condition. I tried reading the voltage produced by the pink/white wire going into this connector and got about 3 milliamps rather than the 4.5 at the white connector. I'm not sure if this is how it's meant to work or I wasn't measuring it properly/had the wrong wire.

I've ordered a new sensor from ebay to try and swap out as a last ditch attempt but I'm meant to be going on a 3000+ mile tour end of next week so won't have time to replace the entire loom as that manual suggests.

I'll have a go at a resistance check on the sensor but I'm pretty terrible with the electronics side so not sure how accurate my readings will be

Any other suggestions based on the above info?

Thanks

[Barney626]

So I just went out and attempted a resistance test at the white connector.

I unplugged the sensor and set the multimeter to measure resistance, placed the probes on the ground (Black/white) and +ve (Orange). For the plug leading into the harness I got a reading of 30k ohms.

For the plug coming from the sensor wire I got an infinite resistance reading. Suggests to me that the sensor wiring is fried?

Is the 30k ohms normal for that loom connector?

[maviczap]

Have you checked the connector isn't corroded, could be a source of your resistance?

[Seeker]

I had linked to the wrong page earlier, the page you needed is here. Unfortunately the test is a bit trickier than the crank position sensor which I'd linked to before. I'm assuming you don't have a 1k ohm resistor lying around.



https://www.manualslib.com/manual/80...age=409#manual


Your resistance measurements don't tell us anything. An orange wire on a Suzuki is usually +12V, so you measured resistance between the battery and ground assuming you were measuring in the loom direction and not the sensor direction. The manual doesn't quote a resistance spec for the speed sensor.


I did find this...
https://www.youtube.com/watch?v=H7d9fukFccY

[Barney626]

Originally Posted by maviczap

Have you checked the connector isn't corroded, could be a source of your resistance?

Yep already looked. The connectors don't seem corroded at all, no where near what could cause this issue I dont think?

[Barney626]

Originally Posted by Seeker

I had linked to the wrong page earlier, the page you needed is here. Unfortunately the test is a bit trickier than the crank position sensor which I'd linked to before. I'm assuming you don't have a 1k ohm resistor lying around.



https://www.manualslib.com/manual/80...age=409#manual


Your resistance measurements don't tell us anything. An orange wire on a Suzuki is usually +12V, so you measured resistance between the battery and ground assuming you were measuring in the loom direction and not the sensor direction. The manual doesn't quote a resistance spec for the speed sensor.


I did find this...
https://www.youtube.com/watch?v=H7d9fukFccY

Yeh sadly I don't have any resistors to test the sensor. By the time I could get one and set it up I should of had the new sensor delivered anyway.

Already watched that video a number of times but havent got long enough leads to do some of the stuff he did really.

I'd say it's fairly likely a new sensor will fix the issue, but lets say I get the sensor and it keeps doing it. Where could the fault possibly be if the two connectors at either end of the loom look fine? Don't see how the middle section could be damaged so badly?

[Seeker]

Originally Posted by Barney626

I'd say it's fairly likely a new sensor will fix the issue, but lets say I get the sensor and it keeps doing it. Where could the fault possibly be if the two connectors at either end of the loom look fine? Don't see how the middle section could be damaged so badly?

When I worked for Creo (they made pre-press equipment for commercial printing), we had a training instructor who would set faults on the equipment and then make us sit and list several possible causes for the symptoms in order of likelihood before being allowed to touch anything. I used to hate it, I've always needed to lay my hands on.
Anyway, what else could it be (in no particular order!).

1) An intermittent break in the cable
2) It's counting pulses so a problem in the speedo counter.
3) The speedo supplies power, maybe it's unstable, you should be able to measure that as per the video.
4) I'm out, I hope it's the sensor

I also hope you got the correct one with either 4 or 8 pulses depending on year.

Originally Posted by Barney626

Already watched that video a number of times but havent got long enough leads to do some of the stuff he did really.

...easy to make, though.

[Barney626]

Originally Posted by Seeker

When I worked for Creo (they made pre-press equipment for commercial printing), we had a training instructor who would set faults on the equipment and then make us sit and list several possible causes for the symptoms in order of likelihood before being allowed to touch anything. I used to hate it, I've always needed to lay my hands on.
Anyway, what else could it be (in no particular order!).

1) An intermittent break in the cable
2) It's counting pulses so a problem in the speedo counter.
3) The speedo supplies power, maybe it's unstable, you should be able to measure that as per the video.
4) I'm out, I hope it's the sensor

I also hope you got the correct one with either 4 or 8 pulses depending on year.





...easy to make, though.

I'm going away for the weekend so will have to just see when I get back. The ebay page advertised for 2004-2014 so fingers crossed its the right one for my K5. If it's not surely I can just swap the rotors over as they're the bits with the magnets in?