Well, I have just been dealing with the CEL and about 2-5 MPG less average for awhile now and have been having only one code -- PO422 3 way cat efficiency bellow threshhold.

Normally caused in these Volvos by clogged PCV system.

I replaced the system and cleaned all the hoses about 2 months ago. Code still comes up.

Vacuum leak was next.

Hooked the smoke machine up tested just about every hose in the engine bay. No leaks other than the PTC nipple (where it goes into the intake hose) located on the intake hose which one of the PCV hoses route to.

^^ it is possable this is introducing too much air after the mass air flow (MAF) and introducing more air than the MAF calculated, thus screwing with everything.

After that was EVAP system leak.

Again, smoke machine found nothing. I had suspected a dry rotted "j-hose" but the hose was pliable and test resulted in notta.

SO........

O2 sensors, watching the voltage output values with a computer I noticed yesterday that the upstream sensor seemed to read high indicating the possibly of a rich engine condition (actual values fluctuated between 1.16 and down to .84 volts generally but never lower than .80v with engine at operating temp.)

The downstream O2 showed a steady .20v and NEVER fluctuated -- as though it wasn't doing anything. Of course this was engine running in park, no load, might be different going down road.

The above being said really confused me because the cat was removing a lot of the emissions and outputting lean emissions.

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Looking for some other opinions in what I have found.

 

I'm having the code as well. I was told that it's either the rear o2 sensor or a bad cat. I just replaced my rear o2 sensor with a used one.

I replaced my PCV system about 20,000 miles ago (10 months). I also tried to clean the cat by driving with lacquer thinner through the gas tank.

When reset it usually takes about 400 miles to return.

 

30 miles exactly for me.

What is odd is that it would only one on if I drive lightly, if I drive hard IE. approach 4,000 RPM while accelerating the light would never come on.

Also, according to a Modius scanner I have been borrowing, the rear sensor is in an open loop state whereas the upstream is in a closed loop state.

 

I don't think my scangauge will show me that. I'll try to check it with my other gauge.

 

Seen bad O2 sensor(s) give this code; remember a thread that went into detail on this; will dig it up if I can.

If rear sensor is flat-lining then it's bad; yes?

Again, using used O2 sensors is like shooting craps; you might get lucky.. Still probably better odds than cheap aftermkt crap out there..

 

wasn't O2

o2 functioning fine while driving down the road.

Voltage from upstream is way high.

Found that after sealing the leak at the valve on the intake hose with silicone, the voltage value went back to normal. Still waiting to see if the code come back. That was done 200 miles ago....err monday.

 

Valve on the intake hose?

 

PCV preheater valve. I will take a pic tomorrow when its light out.

 

....forgot picture.

anyway Friday left for about a 1,000 mile round trip.

on the outgoing drive no check engine light. MPG were steady at 34 MPG, mild hills, 70-75 MPH.

about 30 miles from my destination the light came back on. I assume it is the PO422, but am yet to scan the code.

Computer went into preset parameters -- MPG went down to 28 MPG on return trip, no change in driving style, same roads and traffic.

So, next step is to remove the intake hose and seal the valve from the inside if the code is the same.

I could still have another leak elsewhere, but we shall see.

Now finding 30 minutes to actually do the task is another story.

 

I haven't seen the code since I replaced my rear O2 sensor but I have been struggling with the cruise not working. I think I have disconnected the battery a few times and have not put 400 miles on the car without the battery being disconnected which could be resetting the ECU delaying a code.

 

well when I sealed the valve on the intake hose the code stayed out for about 430 miles, rather than 30 miles like before. SO something I did, and it could have been sealing that valve fixed it.