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most speedo's now run off the ABS. is the air gap right & were they from volvo or aftermarket?
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no i have put the sensors on the right wheels, and it is the haynes manual that suggests the sensors send a speed signal to the ecu which in turn send it to the speedo.
i did take the instrument binnacle out (clockset etc) to replace the abs warning bulb aswell but surely if i didnt put the 2 multiplug connectors back on right then the speedo would either work or not work at all??.
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What was exactly wrong with the old sensors, please expand on out of tolerance. Was the speed read higher / lower on the old one. When you say 50% out on the new sensors, was the speed faster or slower?
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^^^^^^^^^
the rear sensors were giving an open circuit and a 0 resistance reading on the multimeter indicating they were broken,
so i replaced with new rear sensors (come as a connected pair) which cured the fault.
so when i replaced the front sensors (i got them very cheap so decided to do the lot)
the speedo now reads around 50% too slow ie: readout of 30mph when doing 60mph.
can i assume it must be the air gap between reluctor wheel and sensor tip that is wrong and i have inserted the new front sensors too close??.
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I'm clueless now...
Its probably the speed probe (sensor) is of a poor quality that gives you degraded signal. i.e. ideally the signal should be a sinusoidal waveform, but some cheap / faulty sped probe may produce a non-perfect sinewave. So your speedo conditioning circuit may not detect it properly. I agree with your thoughts, try and varies the air gap to see it make any difference.
Is the rear sensors the same as the front? If, can you try ans swap them over and try?
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^^^^^^^^^^^
"Is the rear sensors the same as the front?"
no such luck , totally different unfortunately, all four new sensors are genuine volvo items though.
im just praying its something to do with the airgap, ill spend tommorrow fidling with them and adjusting the depth i put the sensors into their holes/home
i wouldnt mind but i ve googled every combination of words relating to my problem expecting at least one forumite somewhere has had the same problem but....nada nothing at all!!
im thinking now , i need to get it fixed before i get done for speeding lol.
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So we have new sensors all round and the speedo is reading wrong.Do both the Abs and Tracs lights go out when driving?If they do,then I can,t see the sensors being incorrect or air gap wrong.
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^^^^^^^^^^^^^^^
it dosent have tracs, the abs now works (tested at low speed with 2 wheels on grass) but the abs light is still on, the trouble is before the sensor swap the speedo was working fine??
smart money says it the abs ecu...but when that goes bang the speedo just dies a death completely , so this is one hell of a unique problem lol.
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OP, you have lost me now...
You haven't explained the whole story. Now you say the abs light is on. You didn't mention that before..(unless I missed it in the thread)
From what you're saying (tested on grass), it doesn't mean all the 4 wheels are working. I suspect the abs light is still on because the sensor(s) on the front / rear is still upsetting the abs ecu. It may even be the abs ecu affecting your speedo reading (if its faulty).
Can you try disconnect the wire to the abs ecu to isolate the connection?
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