I have this problem with my RPM gauge
Its not working smoothly like it should when I accelerate it goes up but not smooth it cuts or glitches when it goes up or down
Its it something electrical? Or I have to change the whole thing
I found this below online for a Volvo 2019 VNL. If a scan tool were hooked up and the tach reading was steady then I would say that your tach head/cluster is bad.
This truck doesn't have an individual tach signal coming to it. The engine speed is broadcast on the 1939 datalink from the ECM and given to the instrument cluster. If the rest of the cluster is operational, but there is no speed you can connect a scan tool and monitor engine speed. If you're reading it on the scan tool, but not the dash, you've likely got a failed cluster.
I will take it to a mechanic because that’s just beyond my ability also i think it’s something with the wiring because i still have a problem with my left signal I changed everything including the LCM and new headlights and still not working