Hi everyone! Happy Friday!

My car started just yesterday started running in limp mode and throwing the following codes:

P1131 - bank2 internal resistance to high
P0431 - Warm Up Catalyst Efficiency Below Threshold (Bank 2)
P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0306 - Cylinder 6 misfire.

Above 3300 on a fairly aggressive throttle, the engine shudders, stutters.

I'm thinking for P0306 I should replace the coilpack or swap from another cylinder to see if it clears 6.

Not sure for the other codes whether I should start by replacing the Front Driver's Side O2 sensor.

What do you guys suggest?

Please help me make my Saturday a better one by helping me fix this AWESOME machine.

G.Thanks.

 

Yes for the misfire swap the coil pack with another and see of the misfire switchs on you. If not try new plugs.

The cats on your car are not at the same effiency as before when they were fine. Basically you need new cats. Do you smell any rotten eggs? Changing the 02 sensors won't help. 99 percent it's the cats. But it's a small possibility the 02 sensor is bad.

If you are not having any loss of power or hesitation after you fix the misfire then that's a sign your cats are good. There was a ecu update that I think applies to the 2.7 about tuning down the Ecus requirements for the cats at the dealer.

If that doesn't help code the cats out of the ecu by a tuning company. Then you can gut them or whatever.

Also you can try running spacers on the 02 sensors. That will make the 02 sensor not directly hit the exhaust gases so it can trick the ecu into thinking the Cats are ok.

 

Budhani:
Thanks for the reply. As you suggested, I'll start with the coilpack and then the plugs.
If still misfiring, I'll assume cats are gone.

If cats are gone, and I have a tuner ignore them, will I be able to remove or bypass them? I'm a little unclear on options available for handling cats. As well, ultimately, I want to be able to pass emmissions test in the future.

Thanks so much.

 

Forgive me for being "that guy," but you might have better luck posting your questions in the S4 forum. Not many of the 2.7T experts frequent the A4 boards. JM2C!

 

Bad secondary O2s are not uncommon on a B5, and if you're shooting from the hip, replace them (at $60ish each for universals) before dropping a grand or more on cats you may not need. And if it's cat efficiency, it is the secondary O2s, not the primaries, that would be bad.

 

CCA4: Thanks for the advise. I'm getting pretty good advice here as well so I'll hold off from posting in the S forum for now but thank you.

ImTheDevil:
Thanks for replying with advice. I read several posts that eluded to the front o2 sensor, related to P1131. You're the first to recommend replacing the secondaries. It does make a lot of sense for the efficiency codes though so I'll go ahead and order those up as well.

Is it possible that the Cyl 6 misfire code could cause efficiency codes to fire?

Thanks a bunch.

 

Yes - if you're misfiring your mixtures won't be right so it's possible, but fixing it isn't too likely to clear the efficiency codes. But yeah, cat efficiency is measured by the secondary O2 sensors. The primaries are ahead of the cats so they don't have a clue what the efficiency is like.

 

All right. I've ordered up both secondary sensors, 1 coilpack, 1 front o2 sensor (just in case), with discount from Carquest for $504, all OEM mfg.

I hope I don't jack the car up more since it is my only ride and will have to drive all week on it.

On a side note, do you guys recommend running SeaFoam or equivalent through the systems?

 

And the spark plugs...