2000 Q45 Check Engine Soon, P0421 P0422

[m45.sport]

Hi.

I got the "Check Engine Soon" indicator come up and after checking for DTC with my scanner there are two codes: P0421, P0422 (Catalyst efficiency below threshold in both banks). Is it about O2 sensors, injectors, catalytics or something else? Please advise.

[Lokim]

Get a scanner w/ a live data stream on the car. Check the switching of the upstream (B1S1, B2S1) O2 sensors vs. the switching of the downstream (B1S2, B2S2) sensors and make sure they are switching opposite each other. If the downstreams switch low/high at the same time as the upstreams, the cats are going bad. If the upstreams switch fast and the downstreams slow, replace the downstream sensors, and vice-versa. O2 sensors go bad far more often than cats...

[m45.sport]

Lokim, thank you for your reply! I have a scanner and I watched the livestream values. The O2.12 shows almost the same values as O2.11, just a little lower (like if O2.11 shows 0.801, then O2.12 shows 0.680 and so on). O2.22 shows values up to 0.160 all the time no matter what values O2.21 shows (from 0.060 to 0.900). If I had leaked injector before (it was fixed by replacing the injector) could this problem made catalytic bad and that's why the O2.12 shows such values? So basically the catalytic has to be changed, right?

[Lokim]

B2S2 seems OK, but sluggish. Probably a bad sensor. Bank 1 looks like a bad catalytic converter. Bummer, but it could be worse! Glad I could help. It sounds like bank one is running rich. Figure that out before you replace the cat, or you'll be replacing it again before too long. Bear in mind, the downstream sensors will likely have a narrower switching rage than the upstreams. For instance, the upstreams are switching between as low as .05V to as high as .9V and the downs would be between .35V and .65V. The purpose of the cats is to convert bad emissions (i.e. NOx) to simpler emissions (i.e. N & CO) as well as burn up any unburnt fuel from combustion. If they are overloaded with unburnt fuel, they will foul. Good luck! Let me know how it turns out...

[m45.sport]

Thank you, Lokim!

[BadQ45t]

How many miles do you have on that 2000? Just wondering, I haven't had any issue yet at 93k on my 97' but when I do new plugs I am thinking of O2 sensors at the same time.

[Lokim]

How many miles do you have on that 2000? Just wondering, I haven't had any issue yet at 93k on my 97' but when I do new plugs I am thinking of O2 sensors at the same time.

You can get four-wire Bosch universals for cheap @ RockAuto.com. All you've gotta do is wire the connector to match the stock configuration. New O2's @ 90+K are ALWAYS a good idea...

[Lokim]

m45- I forgot to mention, after you figure out and repair why bank 1 is running rich, get the car on the highway for 25+ miles at 60+MPH and when you get back home, leave the car running and read the O2 values while the car is HOT! You may actually be able to blow the crud out of that cat with high RPM driving if it isn't too bad...

[m45.sport]

m45- I forgot to mention, after you figure out and repair why bank 1 is running rich, get the car on the highway for 25+ miles at 60+MPH and when you get back home, leave the car running and read the O2 values while the car is HOT! You may actually be able to blow the crud out of that cat with high RPM driving if it isn't too bad...

The compression in cylinder #2 is about 1/2 compared to other cylinders. I think this is a problem. Looks like it's a valve.
If it's a valve, what would you do? Repair heads? Engine swap? Something else?

[Lokim]

Do a leakdown test on that cylinder. If you hear air escaping into the oil pan or V.C., the rings are bad. If air is escaping via the intake = bad intake valve, same for exhaust. Pull the V.C. after the leakdown if it's coming from intake or exhaust and check and see if an HLA is stuck all the way pumped up...

[oldmako]

How many miles and what the condition of the engine? I'd be far more interested in having the head(s) reworked than replacing the entire motor, but that's just me. Replace it with what?? Something yanked from a wreck or ?????

That is a big can of worms if you "axe" me. Not one I ever intend to open. When I hit 250K the old gal is headed for the glue factory.

**Not sure why this post is here, I intended it to be on a different thread. Hal must be acting up again.

[BadQ45t]

We're all asking how many miles! I will pick up some 02 sensors for my plug change sometime soon.

[m45.sport]

Do a leakdown test on that cylinder. If you hear air escaping into the oil pan or V.C., the rings are bad. If air is escaping via the intake = bad intake valve, same for exhaust. Pull the V.C. after the leakdown if it's coming from intake or exhaust and check and see if an HLA is stuck all the way pumped up...

I'll do it, Lokim, good idea.
The car has 160,000 miles approximately, I was driving the car with leaking injector for couple of days (stupid me), otherwise this would never happen.

[Lokim]

If you have a stuck HLA (stuck pumped up, not collapsed) just dump 8oz of MMO (Marvel Mystery Oil) into the crankcase and run it around in 2nd or 3rd gear above 4K for a few minutes, that may loosen it up.

[Lokim]

Remember to change the oil afterward!