Like most modern cars, this one has emissions controls to prevent gasoline vapors from leaking to the atmosphere. Gas vapors from the sealed fuel tank are stored in a charcoal canister near the front of the car where a valve opens to release them into the engine intake manifold at a prescribed time (typically when the engine is warm and revving above idle) to combust.
This evaporative emissions system has a lot of potential for leaking so it is monitored by the engine controller which looks at pressure in the fuel tank at certain times. If pressure is too low, a check engine light will come on with a corresponding error code (large or small leak).
Intermittently we get a check engine light with P0455:
On Board Diagnostic (OBD-II) code reader shows this to be a large leak:
Some owners might live with this as a nuisance problem but it is likely to get worse and the car cannot pass state inspection with such a problem. Resetting the fault also resets all engine monitoring systems, which require certain drive cycles to be happy. The car cannot pass Texas inspection unless the monitors are OK, so this is a potential show stopper.
Two common leaks on this model involve two different hoses which can deteriorate or split with age, heat and vibration. The easy one is up front, between the radiator and engine. This connects the evap purge valve to the intake manifold. This hose was in bad shape and starting to come apart:
Replaced with new hose but I doubt this is the real problem causing the error code since it was probably not leaking bad enough to trigger a large leak code.
Most likely the problem is a short hose on top of the fuel tank. I experienced this on my other Volvo 850 and it has the same symptoms. Besides the error code, there is a strong fuel odor in the rear after filling the tank, even outdoors after driving a while. This is a much bigger fix because the fuel tank has to be dropped to access the hose.
First remove the cover from over the fuel pump from inside the car. On wagons this is under the rear deck:
Next drain the fuel tank to lighten it for removal. This can be done by siphoning but since I had to get to the pump, it is easier to use the pump itself to push gas out through a length of 1/4″ ID tubing:
First you depressurize the line by running the engine with the fuel pump relay (103) pulled. Then pull the yellow striped hose fitting up and off. This plastic spark plug boot puller works great for pulling the fuel fitting off the pump:
Then connect the tubing and then hard-wire the fuel pump to run by bridging these two terminals of the relay with some needle nose pliers or something:
Ignition needs to be switched on with a key to run the pump. Jump the pump until it starts to go dry (foam coming out).
Once the tank is empty, the four cables on top of fuel tank (fuel pump, pressure sensor, level sensor and something else) must be disconnected:
Raise and support the rear of the car, then unclip the retaining ring at the fuel door to free the filler neck:
And push it through the fender to allow it to drop:
Support the tank in the center with a floor jack and remove three bolts securing the tank straps to the chassis. Lower the tank to the ground where it can be worked on:
The tank can be completely removed by disconnecting four hoses from the underside of the chassis but in this case it is easy enough to work on it in place below the car.
The suspected hose is this one running across the top of the tank with a blue elbow into the tank on left coming from the fuel filler overflow tube on right:
After removing this hose and examining it, a crack is obvious. This is what I expected and is likely causing the error code when filling up:
Replaced with a new factory hose. Because this has two different sizes at the ends, it’s hard to make ordinary fuel hose fit, so I ordered the factory part. Replacement hose is much longer so needs to be cut to match:
New hose installed and hopefully that was the only leak under there:
Raised the tank back up and bolted it snug. Even empty that takes some fussing and wiggling around. Had to feed the wires up through the hole as the tank was raised near the rear deck and also had to guide the filler pipe up into place behind the right rear fender. Secured the filler gasket into the cutout in the fender and re-installed the retaining ring.
After putting a couple of gallons of fuel in the tank I ran the engine to check for fuel leaks before buttoning up the fuel pump cover and all the panels inside the car.
No more fuel smell and no more error codes we hope; time will tell.
This is a very expensive dealer repair ($400+) so once again, DIY is the only way to go.
$11.14 purge hose; $14.78 tank hose
Update 4/24/14: I strongly suspect that lowering the tank (which can’t be avoided with this repair) also causes the rear-most evap hose to crack at the roll-0ver valve. See post #92 for details. Don’t be surprised to have to change at least that hose as well when this one is repaired; it gives the same result (P0455 error code).