On coming to halt my Honda Civic (1995 1.6 LS) has been applying the ABS (i.e. brake pedal reverberating hard). At all other times the braking is A1. The local garage diagnosed a leaking master brake cylinder, but a new one has made no difference. The ABS light is now permanently on. Any ideas what this might be?
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Most likely thing is the wheel speed sensors having a low output. Output is dependent on rpm (i.e. the signal is bigger the faster the wheel rotates). If a sensor is going bad then it will give insufficient output at low rpm leading the ECU to infer that the wheel is locked and therefore energising the ABS hydraulics when coming to a halt.
Try measuring the resistance of all of your ABS sensors (use a DMM) - the 'odd one out' is likely to be the faulty one. Also check all of the connectors in the system.
HTH
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Shouldn't the frequency change with wheel speed rather than the voltage?
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These are a 'variable reluctance' type sensor - so frequency increases *and* voltage. Voltage is proportional to rate of 'flux cutting' by the reluctor ring (this is Faraday's Law of electromagnetic induction).
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Quite right - been a while since I last looked at Faraday's Laws! Also, thinking back to my time on truck ABS we used a sensor simulator connected to a sinusoidal signal generator. The simulator was, in fact, a small transformer and I only ever simulated an ABS event by a rapid change in input freqeuncy.
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Thanks for all of this - much appreciated. I only hope my garage understands it when I take it in tomorrow! I'll let you know.
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your car has a broken sender ring and it needs replacing the rust has expanded behind it and its cracked apart so the sensor sees the extra gap and thinks that the wheel has locked up and puts the abs on!
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HTH - just to let you know you were absolutely right. Readings from 2 front sensors were 75 and 800, rear 2 were both 900, when I gather a reading between 600 and 1,100 is what they need to be. So one new sensor later and we should be done. Thanks.
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SnowyHonda
The 'HTH' at the end of my message meant 'hope that helps' - its not my initials!
Glad to help out anyway - keep the cash in your pocket rather than give it to the Honda dealer!
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