peugeot 206 rev counter reads higeher than its revving?

[Jonno2212]

I have a peugeot 206 1.6 1999 when revving above 2'500 rpm the rev counter gains revs so it revs as normal but displays at 1'500 rpm and so on, this also happens on under revving it looses, but flicking the ignition on and off eventually resets itself and displays revving at 650rpm.. I rang peugeot and said that they would need to put it on a diagnostic of £103.00 which i thinks pretty hefty charge.. I think its the sensor in the gearbox would that cause this? Or would it be the gauge module in the dash?, cheers in advance jonathan

[anonymous-user]

The rev counter is almost certainly driven by a square wave frequency signal coming from the engine ecu, hardwired into the back of the dash cluster. This will consist of a frequency that changes in proportion to engine speed (usually 2 events per rev, as it comes from cylinder firing events). I'd hazard a guess that a capacitor in the dash has failed, and "noise" being picked up on that data line is causing spurious triggering of the input circuitry in the dash. You can probably fix it either by replacing the dash, or by just adding a small external capacitor to the line (you would have to experiment to see how big a capacitor just kills the noise, but leaves the rev signal unaffected). I doubt if an OBD diagnostic scan will bring anything up (assuming the engine is running fine and not misfiring etc)