Volvo FM ABS

It will either be a bad sensor, wiring or the more unlikely ECU but there should definitely be a fault code if sensors telling you which one.

Without that I would go round and unplug each sensor at the wheel end and check the resistance of each with a multimeter. If they’re all ok I would suspect wiring next.

Something like this saves a lot of time over a multimeter checking everything is alright at the wheel end.

hgvdirect.co.uk/sensormaste … 0wod7_4J2g