Hello and Welcome to justanswer Peugeot..

This could be a dirty sensor yes - it could also be a corroded / faulty trigger wheel - (the pick up teeth for the sensor ) - it can even be wear in the wheel bearing on that side - that will cause a sensor fault to trigger.

So you will need to just check those things through - and also - check very carefully the wiring & connections to the sensor... check the wiring up the loom - its not unusual to get break in the wire.....( the trigger wheel ( and sensor ) cannot really be checked without stripping)

If all checks out as ok above, then the sensor must be faulty itself and need replacing.

As regards XXXXX XXXXX job - it is fiddly - you have to remove the brake calipers to get at the sensor...and the disc etc to get to the sensor to check / change whatever is needed... trigger wheel and so on... Being you have experience - Im sure you can do the job so long as you have the tools etc - Its a good time to check / renew the brake pads / discs if needed...

Im very pleased to have helped you -Let me know if I can help anymore...

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Kind Rgds - MIKE