Hi,just wondered if any mechanics out there would know why the speedometer on my car has stopped working most of the time,it works probably one journey in every ten,have been told that there is a speed sensor somewhere on the vehicle that could be failing, but not sure where or how easy or difficult it is to fix/replace,thanks in advance for any info.

might help to say what the car is…

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Hi, it,s an Opel Frontera diesel 2003.

From this resource

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I can watch the speed from my gps, which I think is more accurate than a car’s speedo….

OH bought a small rechargeable GPS thingie which sits on the dashboard of my old car and it tells me the “speed” regardless of what the dodgy speedometer says (and it works for any car of course).

He decided it was easier than getting the mechanism (whatever) redone… but he might get round to fixing it one of these days.
Being an oldtime-driver, I know the speed by the revs and the music of the engine… but like confirmation that I’m not breaking any limits…

A stand alone GPS definitely is. All vehicle speedos overestimate your speed by several % for safety reasons (I think it may even be a legal requirement), the GPS is accurate. The speedo on the Prado I’m currently renting shows 115KMH for a genuine 110 on the navigation app I’m using. A few years ago I tried to do 200KPH (legally) on an autobahn but my Garmin revealed, despite being flat out, I was travelling at a mere 198 :face_with_hand_over_mouth: So, that’s another challenge yet to be achieved.

Years ago, I heard on the radio that the EU, according to the AA, allowed a discrepancy of around 1.5% on a car’s speedometer.

My own car, Renault Clio, when on cruise control at 90 km/hr, the GPS reads 87kms/hr.

ISTR the legal spec for a speedo in the UK is 0-10%, it is never supposed to indicate less than the actual road speed.

a 60cm diameter tyre, wearing down from 10mm tread to 2mm gives at least 2.7% variance in accuracy.

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