Do XM (non-cable) Speedometers "Flick"?

[addo]

My 605 has taken up a strange habit.

From around 25MPH to 50MPH (haven't been any faster in it at a steady speed to investigate) the speedometer sometimes flicks up, then slowly sinks back down to correct. Then flicks up again.

The temp and oil temp gauges seem steady, and none of the telltales flicker when this occurs.

Is this also an occurrence in later XM models?

[RichardW]

Later Xantia electronic ones are prone to giving odd readings when the connections to the board are broken (MK 1) or not springy enough / not clean enough (Mk 2). Maybe yours is the same? 50mph seems to be the default speed if the wrong info is being received.

[citroenxm]

Faulty speed sensor id say...

[xantia_v6]

I believe that 605s have an interface/amplifier box between the sensor and the speedo/trip computer/cruise control/suspension control, which the citroens don't have. this would be an additional possible failure point.