Nillbymouth Posted September 9, 2015 Share Posted September 9, 2015 Yet another speedometer not working post but I've searched previous threads and suspect my problem is slightly different:1. Sigma 140 with electronic speedometer.2. Has, until yesterday, worked flawlessly with none of the dropping out that others have mentioned.3. While driving yesterday, one minute it was working, the next it wasn't - there was no period where it was intermittant.4. Digital miles readout still shows but is not recording any more miles.5. When I turn the ignition on the speedometer needle 'blips' so it is getting power.6. Checking the sensor at the rear wheel, it lights ups as the wheel turns.7. Unplugging the sensor and checking the +ve and -ve wires its showing 12v so it is being fed the correct voltage.8. No sign of crimped or broken wires.There is talk on other threads of an internal fuse in the speedometer but I guess that is okay since the needle moves when I turn the ignition on.I could try the new ground mod but since I've not had problems before this I'm not sure that is the case.So what can be the cause? Any suggestions greatly appreciated. Link to comment Share on other sites More sharing options...
mschraider Posted September 13, 2015 Share Posted September 13, 2015 Did you find a fix for this ?I seem to have the same issue, and have done the same checks. Link to comment Share on other sites More sharing options...
Nillbymouth Posted September 14, 2015 Author Share Posted September 14, 2015 Not fixed yet but I've come to the conclusion that it's the sensor or sensor wire that is broken.I disconnected the speedo and checked for continuity through the loom from where the sensor plugs in to the speedo plug and that is okay.I then connected the sensor to 12v and checked the output. Although this is a digital output I'm sure that when the sensor light comes on it should be outputting about 5v. I get nothing. This test may be wrong so if someone in the know can correct me - please do.So, I'm just about to order a new sensor and see if that fixes it. Link to comment Share on other sites More sharing options...
John Vine Posted September 14, 2015 Share Posted September 14, 2015 When you say " it lights up as the wheel turns", do you mean that the LED pulses on and off as each tooth of the reluctor ring passes by, or that it's on all the time?JV Link to comment Share on other sites More sharing options...
Leadership Team Garry7 Posted September 14, 2015 Leadership Team Share Posted September 14, 2015 The sensors are notoriously fragile, my 4th in 3 years failed on the second day of the Italian Tour, leaving me with sat nav for speedo - great in the many tunnels we encountered!It will cost you around £65 for the priviledge too :((( Link to comment Share on other sites More sharing options...
Nillbymouth Posted September 14, 2015 Author Share Posted September 14, 2015 It does as it is supposed to do - flashes as the wheel turns - on when the high point of the reluctor is near the sensor and off at the low points. I even tried moving the sensor to both extremes - almost touching and as far as possible while still lighting up.I've now spoken to Caterham who also suspect it's the sensor. A new one is on the way and I'll update once I've tried it. Link to comment Share on other sites More sharing options...
Nillbymouth Posted September 17, 2015 Author Share Posted September 17, 2015 New sensor arrived from CC yesterday. Before fitting it I connected it to a 12V supply and tested the output. It showed 0.33v when LED was off and 0.77v when I put it near some metal and the LED was on. The old one showed 0v regardless of whether the LED was on.Fitted it and I now have a working speedo.I've just done a bit of investigation and think that this is the actual sensor:http://uk.farnell.com/schneider-electric/xs108b3nal2/inductive-sensor-2-5mm-12-24vdc/dp/2455529From Farnell it's £43.47 instead of Caterhams £69.60 but you'd have to put your own plug on it. Link to comment Share on other sites More sharing options...
BigCol Posted September 17, 2015 Share Posted September 17, 2015 I suspect I am about to join this gang - the speedo on my 2013 140 Sigma works only intermittently.I haven't analysed the situation but it seems to fail at higher speeds, say 50mph+ but work OK in/around town.Does this sound like the early stages of a similar fault? Link to comment Share on other sites More sharing options...
John Vine Posted September 17, 2015 Share Posted September 17, 2015 Does this sound like the early stages of a similar fault?I would say it's caused by either (a) the airgap (too big/small) between the sensor and the reluctor ring, or (b) interference in the loom between sensor and speedo. At a guess, I'd say (b) was more likely.For (a), check that the gap is in the range 0.5mm - 2.00mm.For (b), apply the "earth mod" as set out in CC's Workshop Notice 572. This sets up a chassis earthing point much closer to the sensor. If you need a copy of WN572, send me a message.JV Link to comment Share on other sites More sharing options...
BigCol Posted September 17, 2015 Share Posted September 17, 2015 Thanks John - will send you a BlatMail (or equivalent) to request the info on that mod. Link to comment Share on other sites More sharing options...
Nillbymouth Posted September 17, 2015 Author Share Posted September 17, 2015 I'd agree with JV.Mine worked perfectly at all speeds then just suddenly stopped working. There was no stage where it worked intermitently. Link to comment Share on other sites More sharing options...
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