Help with code troubleshooting

[01_Nautic_V70]

Hi,

I purchased a 2008 XC90 V8 3 weeks ago and have just recently had a few codes come up. A week ago, I got P0420 and P0430 codes for Catalyst System Efficiency Below Threshold Bank 1 and Bank 2, respectively. I reset it but it has come back Was hoping to get some time this weekend to get under the vehicle and look for exhaust leaks or perhaps an intake or vacuum leak up top.

Then, today, I got in and it wouldn't start. Crank, no start. I tried again, and pressed the accelerator a bit. It did start. The engine idled a bit rough, but smoothed after a minute. I started the drive home. A few blocks later, the check engine light began to blink and the Info Center read "Slow Down or Shift Up". The tach read 1,500rpm and the sound was consistent with that.

When I got home, I pulled the following codes via VIDA:
P0420 Catalyst System Efficiency Below Threshold (Bank 1)
P0430 Catalyst System Efficiency Below Threshold (Bank 2)
P0335 Crankshaft Position Sensor A Circuit
P0300 Random Misfire Detected
P0301 Cylinder 1 Misfire Detected
P0302 Cylinder 2 Misfire Detected
P0305 Cylinder 5 Misfire Detected
P0306 Cylinder 6 Misfire Detected
P0307 Cylinder 7 Misfire Detected
P0308 Cylinder 8 Misfire Detected

To me, the central issue here seems to be the crankshaft position sensor. The ECM clearly was not sensing engine speed properly. And inaccurate reading of crankshaft position would cause ignition timing problems, leading to misfires. And misfires would lead to emissions out of spec. So a bad crankshaft position sensor could cause all of the above.

But I do have a few questions. What do you guys think of my logic on this one? Make sense or am I way off? Is the crankshaft position sensor a known issue? Is the wiring to this sensor a common problem?

Thanks for reading, I appreciate it.

[abscate]

These sensors rarely fail on these cars. If you got rough running, it’s not uncommon to code on all cylinders. Clear the codes and see what comes back. What’s the age in the spark plugs and coils?

Fuel pressure sensors go on these., too. Diagnose that with measuring fuel pressure at the rail

[ggleavitt]

Absolutely agree on the above.

There's a guy named phuz over on Swedespeed that has had a ton of misfires in a 2005 over the years. I would do an "advanced search" for misfire and the author phuz, see what you can get from that.

As this is a V8, since you're seeing in on all cylinders it'll be something common to all. Maybe a loose ground, maybe something else. I've seen a whole bunch of posts relating to CPS and misfire, I cannot say that I've seen more than one or two that reported as resolved after replacement.

For sure check the ground (left side fender well is strap for motor, might be another) and make sure everything is tight. And if you want to pull the covers and check the coil grounds, that'll be good too.

If all your grounds are solidly connected then I'll stick my neck out and suggest it's either battery or alternator or both. Depending on what work has been done on this vehicle, you might have some oil leaks that predicate a partial failure of the alternator or you might have had something as simple as a broke 3-way washer tee under the passenger side hood washer nozzle (tech in Canada mentioned this way back in 2010) that's spraying right down onto the alternator but I'll guess this is an electrical issue.

Battery and alternator, would check those for sure and really get a good light onto the alternator (firewall side of motor) to see if it's decently clean. I'll guess it isn't. As to the battery, if it's more than 12 years old, you might consider replacement. I would not suggest that you replace the alternator outright as it's not a trivial job. But somewhere around 135k miles is when both mine have coded, with the Sport getting a few of the "slow down shift up" messages on specific scenarios before the "power urgent" message came up. Ocean Race coded outright before failure and I had a replacement ready and waiting since this was my second V8.

Everything I've read suggests the largest issues with V8 misfire relate to two causes- work just completed on the V8 valve covers (would be 2-cylinder specific) and a failing alternator or not using a genuine Bosch AL0821X for the alternator replacement (would be all cylinders). You could have a possible loose LIN wire (on top of alternator, you need to take the rear covers off to see it) and you'll want to check if someone has replaced the alternator already.

That's what I think.

[01_Nautic_V70]

I have no maintenance history on this car as it was purchased just 3 weeks ago.

Coil issues, alternator issues, battery issues. I could see those causing the misfire codes. But where is the crank sensor code coming from?

I’ll start digging into this this weekend. It’s the first nice Saturday here and the wife wants to do things in the garden and yard. So perhaps I can get to it tonight after dark. I have to split garage time between two project cars right now it seems.

I’ve tried clearing the codes. The pop back up almost immediately. Within just a few miles. They then clear in a few miles and reappear. So they’re intermittent but very frequent. Whatever the cause, it’s happening quite often. The cylinders showing misfire are always the same. 1, 2, 5, 6, 7, 8. So is that the entire rear bank and two front?

I drove this home from the seller a few weeks ago. 350 miles, no issues at all. It was then and has been mostly in the 30-40F range. Just in the last few days it’s been in the 60s. Wondering if temperature is playing a role here.

[ggleavitt]

My guess is the CPS is complaining as it's just part of the scenario. Why cylinder 3 not reporting but the others are? Dunno. What I do know is that I've never seen a "slow down or shift up" message since replacing the alternator and that was more than a year ago.

If this vehicle is new to you, probably smart to get some photos and post mileage. If you're not familiar with this powerplant, you might have some other stuff that's due but I might suggest a good visual so you know what you have as far as leaks for a start. And check the 3-way tee under the passenger side windshield washer nozzle at your earliest convenience, if the cap is broken or even slightly loose, replace. It's PN 31391513 for the 3-way, driver side (2-way) is PN 9178897.

[01_Nautic_V70]

Ok, it seems you guys are correct. Alternator has oil all over it. So Ive ordered and received a Bosch alternator.

The leaks are at both valve covers. So I’ve got the parts on order to do the valve cover gaskets which will lead to new intake manifold gaskets, cam solenoid seals, PCV valve and hoses, fuel pressure sensor and serpentine belt.

Really need to address the oil leak before putting this nice shiny Bosch alternator in and dirtying it up.