So the situation is this my friend has a 2001 S80 I believe the base engine when she got the car she was told one of the cylinder piston rings was bad which means it won't pass emissions initially but shortly after getting it she had a problem with the dash lights cutting out it wasn't just the dash lights it was the dash lights their control and the seat functions what all cut out but it was intermittent sometimes it come on sometimes it would which led me initially to look at the fuses and relays and I dove into some of the forums and it was pointing to a faulty ECM I believe it was the ECM a relay in the ECM that would control all of those well I haven't quite gotten to that yet but now all of a sudden we had a freeze here in New Mexico and when the car froze at her job she tried to take it home that night but the key would not turn the lock and since then all of the door controls on the driver side door have quit working locks Windows everything and now the passenger headlight is out as well but again that is intermittent the door controls are always out but the headlight is intermittent is this also related to the ECM and if so should I just get the entire ECM replaced or should I try to replace the relays that control these functions somebody please help me

 

1. Do you mean CEM? (or engine control module?) But, yes there could be a problem/bad connection in a power relay in a 25 year old Volvo. Start by finding a copy of the factory wiring diagram to be able to trace how the power is delivered to your troublesome items. .
2. Most common thing that causes that is a bad steering column lock. (or worn out key) I used to replace a couple of those a month for "key not turning, or key won't turn all the way to the start position". (you order a steering column lock from the dealer using your VIN (and proof of ownership) It arrives 2 days later and is precut to fit your existing key) There are "hacks" to be able to get a non-turning Volvo steering column lock to work (google is your friend if that's the problem)
3. You do understand that the CEM (and the ECM) if replaced will have to be programmed using a VIDA subscription to talk to the rest of the car. A used part will not work. A company such as xemodex might be able to supply you with a preprogrammed (for your VIN) unit that will work. They will want detailed VIDA/volvo diagnostic codes from your old control unit to make sure they are fixing what is broken with yours. (if that's the problem!)

You should not randomly replace anything. That gets expensive and frustrating. You should find someone with the knowledge (and willingness to work on a car that old) that can pinpoint your problem (s) in a rational, reasonable way using a logical thought process. (if your headlamp is intermittent and it's a HID bulb - there's probably problems with the ballast, bulb or igniter - all expensive. For those swap parts side to side to test each part. If it's a regular incandescent bulb - bad/melted connections at the bulb are usually the problem. Dead drivers door controls could easily be a broken wire in the hinge where it has had to bend almost 90 degrees whenever the door was opened for the past 25 years)