Question edited for clarity.
Question moved to model category.
This is a strange code that doesn't appear to have one definitive reason, it's a bit of "you have a bit of a problem, but we aren't sure". Just Answer dot com mechanic says it is the MAF Sensor.
https://p1004-volvo.autotroublecode.com/http://p1004.engine-trouble-code.com/
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Feb 12, 2022 - On newer vehicles, the P1004 is for the short runner valve which is internal to the intake manifold and makes sure there is even air ...
1 answer · Top answer: HI This is 100% unrelated to your original question. I will answer this as a courtesy, but ...
Question edited for clarity.
Question moved to model category.
You have a leak, you just need to find it.
Look for leaks in the hoses. Do a pressure test.
The most common reasons a Volvo S40 has a coolant leak are loose hose connections, a broken radiator, or a failed water pump.
Cylinder head bolts (D4192T2):
Cylinder head bolts are tightened in two stages. There is no need for retightening.
Follow the order as pictured.
Stage 1: Tighten to 30 Nm, Angle tighten to 50° ±4° in one movement without stopping.
Then wait at least three minutes in order for the cylinder head gasket to stabilise.
Stage 2: Completely loosen bolts 1 and 2. Tighten bolts 1 and 2 to 25 Nm. Angle tighten to 213° ±7° in one movement without stopping.
Repeat the Stage 2 for the remaining bolts in the order 3-4, 5-6, 7-8 and 9-10 as illustrated.
Year of vehicle may help you get an answer as there were many radio changes. Mine has BlueTooth and many don't etc etc etc.
Why not pop into your Volvo Dealership for help.
Buzzing can be an issue with the door lock or central locking mechanism. You could try hunting for where the sound is more accurately. This will sound a bit silly but try this. Sound can travel through solid surfaces so can sound like they are coming from somewhere else. Put your ear against the side of the door panel nearest the handle and lock the car. Your listening to see where the noise is loudest. Listen at the hinge end as well to check if it's actually coming from inside the engine bay rather than inside the door.
Set the emergency brakes and keep the brake pedal pressed during this procedure.
Use a dashboard removal trim to pop up the trim around the shifter.
On the driver's side, on the shifter side, is a white tab, which is the SHIFTER RELEASE.
As you press down on the shifter release, manually move the shifter out of Park. Volvo Shifter Stuck In Park - Manual Release (youcanic.com)
The ROPS suystem is stand alone and does a self test each time the key is turned to the ON position. If the system detects an error, it disables and sets the light. You will need to have the car hooked to a scanner that is able to access the system and find out what is thinks is faulty. Could be a rodent chewed a wire, corrosion at one of the contacts, or an actual bad sensor or module.
This is one of those 'Yes - No' answers. Rear seat that drop were an option on the V40 so the answer could be no. Take a look through the left side of the back window at the rear parcel shelf, next to the left head rest. Your looking for a small push button panel, about the size of cigarette box, with two buttons on it. If it's not there the rear seats are fixed into position. If there is one there you might be able to 'trip' the lock spring from inside the trunk. This method is for a much newer model so it might not work. Look inside the trunk, high up on the rear seat where the flat of the seat meets the parcel shelf. There should be a metal rail going all the way across the car. I've attached a photo. Looking straight up at it there are holes in it and you should be able to see a spring or a cable through one of them. Using a chunky, flat blade screwdriver you might be able to 'flick' the latch to release one side of the back seat. The spring is a strong one sort will fight you. To do this you'll be lying with you legs hanging out of the trunk wrestling with it, Probably swearing a lot as well. If you manage to drop the back seat you probably need a small person to wriggle through the hole as I think the rear seat pad needs to be lifted for it to drop all the way.
There is no access from behind the rear seats.
You can either call your Volvo dealership and they can advise a trusted locksmith or use your spare key.
All Volvos have two keys.
you can use a Stud Remover set, or you put two nuts on the threads and lock them together with two spanners against each other, then undo using the upper nut.
https://www.google.com/search?q=stud+remover+set
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