I got instant OBD failure codes P0245, P0445 and P0448. The cause for this is a blown fuse #5 in the engine compartment fusebox. I've been looking for the cause of the problem, and measure 1.0 ohms (up or down a few tenths of an ohm) at the "output" side of fuse 5... this seems obviously too low.

I've unplugged everything that is powered by this fuse but haven't located "the one". The only thing I do know is that the problem isn't the solenoid valve located underneath the car (it connects to the fusebox on a separate plug, so I was able to ohm it out separately).

I'm thinking it's one of two things... 1) that there is a direct short from the wiring to the chassis somewhere (my looms are crumbling for the most part, though no amount of wiggling them around seemed to do anything to the resistance I'm measuring), or 2) I have mistakenly not unplugged the right thing... I think I unplugged the right plug for the PCV pre-heater (which is supposed to live down on the turbo air inlet under the brake booster), but there are quite a few connectors down in that area, and I might have missed the right one.

Anyway, I thought I'd ping the collective wisdom of the universe here to see if anyone else might have happened to have the same issue. Never know... it could happen!

Oh, and Happy New Year!

 

Yes, Happy New Year!
I'm a newbie here with exactly the same problem on my 2000 V70 XC following an otherwise successful cylinder head transplant with no present symptoms of problems other than the CEL (usually takes a minute or two to come on after being cleared), recurring blown fuse and error codes.

P0136: O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
P0445: Evaporative Emission Control System Purge Control Valve Circuit Shorted
P0448: Evaporative Emission Control System Vent Control Circuit Shorted
P0245: Turbo/Super Charger Wastegate Solenoid "A" Low
P0037: HO2S Heater Control Circuit Low (Bank 1 Sensor 2)
P0031: HO2S Heater Control Circuit Low (Bank 1 Sensor 1)

I'm leaning heaviliy toward the P0445 and PO448 codes as being at the root of the problem and guessing the other codes are merely effects of the fuse blowing, rather than a cause.

But I have not yet resolved the issue. Have you?

 

Nope, I really haven't gotten to the place where I can start troubleshooting my V70 in earnest... I'm sure I can run the problem down once I can start tearing things apart, but it's not something I want to do "on the road" (because of the unintended consequences that can happen when you accidentally mess up something else - the car runs just fine right now, so I'm not going to take any big chances).

I'd say the P0031, 37 and 136 codes are a whole separate issue - obviously something to do with the O2 sensors (or more likely wiring). But the issue you (and I) have is that something is blowing fuse #5, and once that happens you'll get the other codes on start-up every time (P0045, 448 and 245). Something in that circuit is shorted out full-time on my car at least, so it's just a matter of unplugging components and moving wiring until the short goes away, and then fixing the identified problem.

In my case, I just stuck an ohmmeter between the non-powered (output) side of the fusebox connection for fuse #5 and ground. This allows me to read the resistance of that circuit, and it's 1.0 ohms or less (which means it'll draw at least 15 amps without anything else changing). Until I find that short, the fuse will blow immediately and I'll get those same three codes every time. I bought a bluetooth OBD device, and the Torque Pro android app and reset the error codes any time I'm driving any real distances (just so I will be aware of any other problems cropping up).

I'd recommend chasing down the devices that are powered by fuse #5 and checking each of them with an ohmmeter to see if any individual item is shorted... you might find an obvious problem. The other thing that's likely in your case (having just replaced a head) is a short to the wiring for the cam timing solenoid at the passenger side of the head. It wouldn't be too hard to pinch a wire in that circuit while you were swapping the head, or even installing the spark plug cover panel.

Good luck with your troubleshooting, and let us know if you find the problem. I'll do the same, though it's likely to be at least a few weeks before I get time to fix it.

 

That was it. A wire pinched and shorted by one of the two shouldered Torx bolts holding the timing belt cover.
Due to weather, I was expecting it would be some time before I would get around to more diagnosis of the circuits on that fuse, using the errors codes as guides. Although I had not yet looked at that circuit, I was also intermittently getting:
P1655: [Volvo] Camshaft reset valve. Signal too low.

With some warm dry weather I took the opportunity to start there and found the problem immediately upon removing timing belt top cover. Good luck in your quest.

 

KLFVF, congratulations on finding and fixing the problem... glad I could point you in the right direction. I just got back from a 10,000 mile road trip and haven't had a chance to chase down my own problem yet, but now I'll be doing it in my garage and not in some cold parking lot!

 

OK, time for an update! As I suspected, I hadn't actually unplugged the sensor that's down near the turbo, in the air inlet pipe (the one that runs between the air box / MAF sensor and the turbo inlet). There were several others in the area, and I had unplugged each of them, but of course, that didn't do any good.

This morning, I decided to tear all the pipes off the engine and give it a good wash (a dry, compressed oil filler cap gasket had resulted in gobs of oil weeping onto the head, and then down the back of the engine). In the process, I finally located the culprit - the sensor that lives just a couple inches from the turbo inlet on the inlet tube. I unplugged it, and my circuit resistance went from around one ohm to around 20 or so. If you're chasing a short in the fuse #5 circuit and unplugging things, trust me... you haven't gotten to THIS one yet. I don't see how it would be possible to unplug it without removing at least the air inlet tube from the turbo.

Then the fun started... I spent hours trying to find the right part number. It ended up being an exercise in futility, and the local Volvo stealership really couldn't provide much input. Ultimately I gave them the part number for the whole air tube with the sensor attached, and found they had THAT in stock. The part number was 30680446-9 "fresh air pipe". When you look at an exploded diagram, you never DO see the sensor (the angle hides it), but I think it's listed as a "nipple". I have no idea how or why, but if you can get that (and it's the right thing... anyone's guess) it's about $40 cheaper. In my case, there were a few cracks in the plastic tube where it was clamped to the turbo anyway, so I didn't feel bad about spending the extra money ($105.50 out the door).

So now, no error codes, and presumably all the other things that are attached to fuse #5 are happy and working again. Whether that will improve the driveability of the car is anyone's guess (I haven't had a chance to road test it yet, but am heading out the door to put 30 miles on it tonight so will know soon enough).

The one question I do have is where does the big (3/4" OD?) tube that comes off the sensor in question go? For the life of me, I couldn't find anything that it used to be connected to, and the hose is only 5" or so long. I suspect I pulled it off of another hose that fell down behind the motor somewhere, and didn't have time to chase it down. The cool thing is that it apparently vents excess turbo boost to the outside through that little tube, which sounds great...