Repeated P0422. Cat does not rattle. Purge valve or O2?

[matthew1]

I've been getting P0422 every 40-160 miles (drive cycle, I'm sure) for a couple months. Mileage is good/normal, so it's not the front sensor.

Catalytic convertor is not rattling, nor is oil dripping/burning on it -- from what I've read, another reason for this P0422.

So then: purge valve up front on top of fan, or O2 sensor? Or something else?


Thanks
Matt

[Ozark Lee]

It could be a bad rear oxygen sensor or a bad connection from it. Are these OEM sensors or universals? I have seen some problems with the splice boxes on the universals.

Another place to look is at the connectors from the O2 sensors that are, more or less, under the brake booster. They have a funny ZIF socket connector and you need to slide the end out to release them. A shot of contact cleaner on both sides of the connector can't hurt anything.

...Lee

[matthew1]

Lee, they're OEM. The rear is the original. 106k miles. I changed the front in 2002-ish. I still remember the anguish of trying to get that wire harness connector on and off. So you think change the rear, if the connection isn't the problem?

[jblackburn]

If the rear O2 sensor sees varying levels coming thru the cat it assumes the cat is not functioning properly (assuming everything else is functioning properly). The cat efficiency is determined by comparing values from both front and rear O2 sensors.

The easiest way to get to that O2 sensor connector thing is to knock it loose from the metal bracket from the bottom and then pull it loose and fight with it from up top. Course, everything is still right in your way, but it's a bit easier as you have more access to the wires/plugs.

However, I'd check around for an exhaust leak or vacuum leak somewhere. Around the exhaust manifold or cat. itself - you should be able to hear a small leak or feel it with your hand from underneath.

I have had vacuum leaks in lines that have NOT triggered the light for the front O2 sensor or really affected gas mileage much, but noticeably affected how the engine ran (for instance the idle dropping low when coming to a fast stop).

[matthew1]

New clue: no cruise control. Just discovered that today. I never use it, but thought of checking it.

So it's a vacuum line. But which?

My elbows are all ok, not rotted. It's weird, but true. The only thing I can think of is that a clamp on one of the lines is too tight, restricting or stopping airflow. I traced all of them from the TCV to:
1. the big air hose right out of the air box (short hop), blue
2. to the top of the turbo (medium length), green
3. and to the bottom of the turbo (the difficult one) red.

Those lines are ~2 years old.


Intercooler big hose junction, green TCV line is on the extreme left.


BUT, it's got gunk. This is worrying.


And the evil elbow under the intake. Looks good.


And the evil elbow under the intake. Another shot. Evil.


Under the fuel rail right side, right off vacuum tree. Looks good.


Under the fuel rail left side. Looks good.

Any ideas?

[Juan62]

I have replaced: both j-hoses on the EVAP canister, fuel filler cap 3x, fuel filter numerous times, elbows, vacuum lines, and recently this Purge Check Valve near radiator shroud and in front of battery. After more than 200 miles, I still get a P0422 small leak, but I will be replacing this T-shape system (I was told by FCP Groton it comes as a complete kit). If this does not fix my problem permanently, the next thing is to go back to the EVAP canister...there is a Purge Valve that looks similar to the check valve, but more expensive.

Your Purge Check Valve may be round or rectangle, by Peirberg or Denso.

[jblackburn]

P0442 is an EVAP code; P0422 is still a cat efficiency code.

Matt, could be any of several reasons why the cruise control isn't working. Mine was the brake switch, but there is a single vacuum line that dives down under the battery tray for the cruise control pump.

I like the "EVIL" comments on the elbow. Your PTC probably just needs to be cleaned though.

Does your car have an air pump (SAS) system?

[Billc1015]

What year and model do you have?

If it is a late model with an ETM, the cruise may become disabled when the check engine light is on (not 100% sure of this but may be a possibility). The cruise control is all done electronicaly through the ETM so it does use vaccum to opperate.

If it is early without ETM then the cruise has it's own vaccum pump and does not rely on engine vaccum.

As far as the P0422 code, even if the cat does not rattle or have oil in it, it can still be bad. We are frequently replacing cats where I work due to cat efficiency codes. Granted it's not Volvo but when I was at a Volvo dealer, it was not unheard of to have a bad cat once in a while. I would try replacing the front and rear O2 sensors first and if the code comes back you may need a new cat.

Usually vaccum leaks cause codes for the front O2 sensor or codes for short/long term fuel trim being too lean.


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[matthew1]

I have replaced: both j-hoses on the EVAP canister, fuel filler cap 3x, fuel filter numerous times, elbows, vacuum lines, and recently this Purge Check Valve near radiator shroud and in front of battery. After more than 200 miles, I still get a P0422 small leak...

Ugh. My heart goes out to you, Juan. And it might go out to me if this code starts thinning my wallet like yours has. I'd rather do one difficult, dirty, backbreaking job than solve a chase-your-tail-with-your-Visa-card moneypit mystery.

Your Purge Check Valve may be round or rectangle, by Peirberg or Denso.

Mine's round. $80-ish for replacement, already looked into it .

P0442 is an EVAP code; P0422 is still a cat efficiency code.

Justin, thanks for this distinction. You're correct, my code is four-twenty-two.

Matt, could be any of several reasons why the cruise control isn't working. Mine was the brake switch, but there is a single vacuum line that dives down under the battery tray for the cruise control pump.

Ok, so it may be unrelated. I'll look at this line closely.

I like the "EVIL" comments on the elbow.

"Evil" to be perfectly honest is going easy on this elbow's location and orientation. You know it brother.

Your PTC probably just needs to be cleaned though.

Ok, will do.

Does your car have an air pump (SAS) system?

Yes. I need to do Jesse's SAS Delete. I need to keep promises I make before I go around telling others to do so.

If it is early without ETM then the cruise has it's own vaccum pump and does not rely on engine vaccum.

Bill, she's a 1997 850 B5234T, no ETM. Ok, another vote counted toward cruise not being related to this P0422.

As far as the P0422 code, even if the cat does not rattle or have oil in it, it can still be bad. We are frequently replacing cats where I work due to cat efficiency codes. Granted it's not Volvo but when I was at a Volvo dealer, it was not unheard of to have a bad cat once in a while. I would try replacing the front and rear O2 sensors first and if the code comes back you may need a new cat.

and

Usually vaccum leaks cause codes for the front O2 sensor or codes for short/long term fuel trim being too lean.

Ok, great information, thanks.

[jblackburn]

Do the air pump and associated parts WORK? That could be causing the efficiency code right there! (although when mine started going bad, I kept getting air pump codes just about every day or two. Very annoying.)

You should hear it start up in the morning once the car is put in Drive and driven a few hundred feet. I hear mine switch on when I drive down to throw things in the mailbox leaving for work in the morning. It comes on to help warm it up to operating temperature, and will sometimes switch on idling at a stoplight or something.

Or it could be a bad O2 sensor...or a bad cat...