I have been having a terrible hesitation that seems to be getting worse everytime I drive my car. I had this once before and fixed it by changing my plugs, wires and doing a valve cover service.This fixed the problem till 2 weeks ago. The same studdering is back so I took it to a friend with a PathFinder II Diagnostics tool.The value for my O2 sensor for bank 2 was pegged out and wasn't moving. He told me to go to this muffler shop and have them do some other test.

Now my Question: Does this sound like my cat is bad? He said he didn't think it was the O2 sensor itself but rather a plugged cat. I have no weird smell or anything just this hesitation.

As always thanks in advance for any replies I recieve.

We don't have a second bank (bank 2), only V engines do.

Try to get a log of your primary o2 sensor (bank 1 o2 sensor 1) while at WOT, it should stay steady around .91v, if it fluctuates while at WOT then your sensor is probably bad.

Replace the coil. Look in a Chilton's manual or search if you want to test it first to be sure. If it's not the sensor, or coil then it's probably fuel delivery. I would first replace the fuel filter, then run some injector cleaner, and that should clear things up.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

We do have a bank 2 sensor...its the downstream o2. Scanners recognize it as a bank 2.

Sounds like you cat may be clogging. Typically if the downstream o2 goes bad you will not notice any drivability issues so that leads me to believe you have a bad cat. If you drop the cat you should be able to see through the honeycombs. If you cant see through at all then its probaby clogged. A muffler shop can check the cat for you the only problem is if you dont have them money to replace it......you might be screwwed. The reason is they might have to cut the bolts out rendering your cat useless. Go by you tailpipe and see how much exhaust is comming out.....compare it to another 2gnt.

Another option...by a high flow cat and have yours replaced or put on a testpipe and do the resistor mod.

You are getting a CEL right?

Terry

No Man actually I am not getting a CEL this time. The last time I had this problem I was getting a misfire on CYL. 2 CEL, but none this time.

If the downstream o2 was bad (enough to see on a scanner/logger) you deffinitly would get a CEL light...theres no doubt about that. The downstream o2 should read lean but the numbers should fluctuate eer so slightly. If they fail to change at all then you will get a CEL. I dont think they will trigger a CEL if the cat is clogged as long as the exhaust that comes out is lean.

Did your buddy tell you exactly what he saw for o2 values?

Terry

The upstream one was reading in the -0.8 range and the downstream one was stuck at 99.2 as best I can remember. I drove the car some today and it was running fine at first. Yesterday if I gassed on it it would just bog. But today when I gassed on it it would run fine till earlier on my way home. Started the studdering through the rev range again.

Joel Baldridge, ASE Certified Master Technician, Audi Certified Expert Technician

Correct. Usually on 4-bangers they are Bank 1 Sensor1 and Bank 1 Sensor 2.

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2012 2500HD LML

Thanks for all of you guys replies. I will check that plug probably this weekend since I don't have time during the week. I have noticed that this hesitation doesn't start now untill the car gets warm. It also shows up when warmed up and you romp on the gas, no matter the RPM.