For codes ECM 3503, 3543 and 3553, recheck coil pack installation and ground wire for cylinders 4 and 5. A solid ground is essential. Make sure there is no oil or rust. Since you installed new coil packs, I've got to believe it's in the grounding or the 16 year old wiring loom at those two cylinders...

If the transmission was taken care of, it's a keeper.

2001 V70 T5's are a lot of fun to drive but a car that old with that many miles means you better like fixing all the "little" crap.

$3K is about right.

Also the fuel door lock doesn't unlock almost never and I have to open the small door in the trunk and move the plastic lock pin manually. The fault is not in the locking mechanism as I tested the small electric motor and its gears and they are OK, which makes me believe the trouble comes from the ...

Are you sure you have the correct spark plugs? Could these be too long and the piston is actually hitting the spark plug?

I only use Volvo OEM spark plugs and have never had an issue with spark gap or electrode damage.

This works for my 2001 V70, to clear the Service Required light (not the message): 2001 Volvo S80 / V70 / S60 Models (May apply to S40/V40 also) • The service reminder indicator lamp illuminates for 120 seconds when the ignition is first switched on. • Insert key and turn Ignition Switch to position...

2001 V70 T5...same location as yours. The early year P2 V70's I see in the junkyard are also in this location...not sure about later years.

Easiest way to remove the serpentine belt is with a specialty tool...no need for a 2nd person.

https://www.ipdusa.com/products/11344/S ... IPD-124537

You've got a sensor or sensor wiring issue.

This video may help.

https://www.bing.com/videos/search?q=20 ... &FORM=VIRE

Check front cam seals if your 2001 still has the originals. I suspect the intake front cam seal has blown out.

I'd recommend against it.

I have only used Volvo green in my 2001 V70 T5. Never had a leak, or any cooling system problem. Maybe replaced the thermostat and temperature sensor once in 20 years. I'm sold on the Volvo formula. I believe a gallon is less than $30.

Why change now?