1999 Volvo S80 P1633

No dash lights I assume that the cluster is dead and the needles dont move either? P1633 is for vehicle speed signal missing. The only problem with this trouble code is that fault tracing has you look for ABS codes and fault trace from there. Now the dash lights being out could be a separate problem or it can be related? To try and actaully get a clearer picture here, you need to be able to look at the whole network and see if all the control modules are online or not? You also need to be able to scan all the control modules for fault codes. In this case I strongly recommend you take it in to Volvo to have it properly diagnose. The only thing you could try and do is check the connector at the brake control module located in the engine compartment on the left side under the master cylinder. Unplug the connector and check terminals for oxidation. You just need to be very carefull since the connector will be fragile and you could brake it. If it looks ok then you will need a wiring diagram and check for power to the control moduel and check the ground cables and check the CANbus cables for an open circuit. Reconnect the connector and see if the lights come back on in the dash. If they come back on for a short time and go out again, then most likely the brake control module is defective. You can also try this to see if it works? Disconnect the ground and positive battery cables and remove the battery. Touch both terminals together and leave them touching each other for 15 minutes. That should reset all the control modules. Reconnect everything back. If everything works great but if you still have the same problem then like I mentioned before and I strongly recommend you take it in to Volvo for proper diagnosis.

I had the problem with the dash, radio and lights before, I solved it by replacing the LSM(Light Switch Module) which I bought from eBay and everything came back on.