P0422 = (Main Catalyst Efficiency Below Threshold Bank 1)

This code's been thrown several times in the past three weeks. I want to make sense of symptoms to understand if they are related. The engine idle is steady at around 750 rpm. But when driving, the engine hesitates / stutters, but after about 10 minutes of driving the hesitation symptoms go away and the engine purrs at any rpm. What could be happening?

 

Would not normally think they're related but then ....

You sure you have no other codes?

This is a longshot but I would ck your fuel pressure. Low fuel pressure (possibly caused by fuel pump on it's last legs..) can easily cause driveability issues and usually doesn't set diag codes. And this possibly could be an intermittent issue (when cold?).

That P0422 code is your rear (post cat conv) O2 sensor telling the ECM that the cat isn't cleaning up the exhaust as much as it should. Can't rule out bad O2 sensor(s) too.

 

In talking with others they also are pointing to the rear O2 sensor as detecting an inequality between it and the front. Would a full-blown mechanics scanner be able to monitor the real-time output of the sensor to see if it's going bad?

I did have a P0102 (MAF) code triggered yesterday, and my idle became rough to the point of the engine stalling. I'm inclined to think it's unrelated; easy enought to fix.

(i like your motto -- i just want / need to learn how to understand the problems!)

 

Does the rear O2 sensor influence the fuel mixture command? I'm wondering if this could cause the "hesitation / stuttering / surging" that i've been experiencing.

 

If you're interested in learning more about cat convertors and O2 sensors as they are used for OBD2, ck out this post; entry #5; very informative.
V40/V70 Oxygen sensors - Volvo Owners Club Forum

I noticed your's is a 2001 MY; more complex than my cars. Yours is returnless fuel system. There's a fuel sensor in the rail that gives feedback to the pump (as I understand it) so it can modulate the pump ON time to keep pressure where it should be. Other's have had issues with these sensors giving incorrect data to the fuel pump control causing driveability issues. Here's a good link that explains in more detail.
Diagnosing Returnless Fuel Injection Systems

Of course your car also has an ETM which can also cause driveability problems; usually sets codes though..

I would clean your MAF, and again, maybe ck your fuel pressure. A scanner may help; more info is always better... and yes, should be able to monitor all your OBD2 (engine) sensors in real time with one.

 

gdog -- The links you provided are a gold mine! Especially the aa1car.com site. Thank you so very much. I absolutely have to get a scan tool that can display sensor data; this will make my efforts more productive. This will be my next step.

I cleaned the MAF yesterday with CRC electronics cleaner, the morning drive was rough, but the return commute was flawless. I think my opinion is still neutral on if that had any direct influence. I also pulled the spark plugs and examined each one and they were all a light gray/tan ashen color with minimal deposit build ups and no rounding over of the tips, so I interpret this as indicating no serious problem with a particular injector.

 

P0422 = (Main Catalyst Efficiency Below Threshold Bank 1)

I had been dealing with this code being consistently triggered. I changed out my ETM last week (see post "XeMODeX challenge") and discovered the gasket between the ETM and air intake manifold was missing. With the new gasket in place, the P0422 code has not been triggered. Here's the scoop...

The code says the Catalytic converter is not doing a good enough job of neutralizing the emissions. My mechanic says candidate causes could be: bad O2 sensor(s), bad Cat, or an airflow / exhaust leak.

I found an air flow leak. The leak was downstream of the mass airflow sensor. The ECU was being told that X amount of air was being fed into the engine and therefore an appropriate amount fuel must be mixed with the air for optimal combustion. In reality, the engine wasn't getting as much air as it was being measured and relative to the amount of air there was too much fuel. The excess fuel was being dumped out the exhaust, the O2 sensors were detecting the excess fuel and triggering the fault code. As far as the ECU knew, if there was high oxygen content coming down the tail pipe the Cat Converter must not be doing its job.

 

Does all this mean you fixed it?

 

Yes. Problems are gone. The new ETM and having a gasket between it and the intake manifold resolved the throttle + high speed stumbing issue and resolved the Low Efficiency Cat problem.

 

What is an ETM?

 

Electronic Throttle Module.