So... A few months back my 2002 2.7t popped the P0431 code (Warm Up Catalyst Efficiency Bank 2 Below Threshold). With lots of reading and the advice of many on this forum, I determined that it was most likely the driver side post cat 02. I found a factory Bosch replacement with the correct plug and routed it down to the exhaust and back up the best I could over the transmission yesterday afternoon. I left the old wiring in there and cut it back to where it wouldn't be noticed. After resetting the code, the light quickly popped back on after the 2nd start today. I didn't pay much attention to it and decided I would scan it when I got home from work today.

Well, on my way to work, the car started missing some in the lower RPM range. As soon as I felt that, I turned around and came home since it was a pretty rough idle. I ended up staying home and scanning it once more and came up with the following codes...

P0056 (Heated Oxygen Sensor Heater Control Circuit Bank 2 Sensor 2)
P0161 (Oxygen Sensor Heater Circuit Bank 2 Sensor 2)
P0431 (Warm Up Catalyst Efficiency Below Threshold)
P0171 (Bank 1 System Too Lean)

The last one there (P0171) went away when I reset the codes after installing spark plugs this afternoon. Now, I'm not saying spark plugs fixed it, because the other ones that came out were pretty good looking regardless, but I mean that it hasn't come back on yet, just the first three.

I guess I'm looking for advice.... I double and triple checked that I routed the new 02 wiring to the right plug. I verified that the exact same wires/colors were on both the new and old 02 sensor. I verified that I received an authentic Bosch 02 sensor (it even came with anti-seize applied under a plastic cover). Is there a chance that I received a faulty unit? That seems like a long shot.

Thanks for any info that comes of this thread.

 

By the way...

Did coil packs change in 2003? After looking at several other posts, in every picture the packs are much smaller and dont thread into the valve cover with bolts. However, on my 2002, they are super wide and hard to maneuver around vacuum lines and wires. Just a question since I did my spark plugs today.

 

Yeah, they changed when they went from the APB engine to the BEL engine. On the APB coded engines, the power stages are attached to the airbox, on the later BEL coded engines the power stages are integrated with the ignition coils.
There's conversion kits from the old style to the newer style that can be done, but I've read that it costs several hundred dollars.
edit: Not sure what the conversion entails, as I have an '04 2.7t. New valve covers and wiring harnesses maybe? Plus the coil packs? Dunno.

 

I would check to see if the O2 wires didn't detach from the plug or O2 itself, or got jammed/cut somewhere in between(routing the wires incorectly?!, since Bentley seems to think you need to remove the engine to replace the post catalytic O2). For that reason many people just buy a universall Bosh O2 sensor, and splice it in right at the O2 sensor so that they don't have to deal with the wire routing...

Secondly I would change the pre cat sensor too on that side, if the other O2 checks out(wires are still connected to it) because the pre cat sensor tells the engine to run rich in the first place, and toast the post cat O2 and/or the cat.

As you probably read already, that code also might mean the cat is toast. But in one instance someone had a vacuum leak(at the vacuum reservoir) that threw this code.

Also, consider this Ross Tech article http://wiki.ross-tech.com/wiki/index...5/P0431/001073

 

The first thing i would do is see if there is 12 volts to the heater circuit. You can easily compare one side to the other and see if you get the same readings. I can't quite remember but i think the heater is the two white wires maybe, someone will know ..

After you have verified if you are getting 12v to the heater of the o2 sensors or not you can reset the codes and swap them over. if it is the same as mine the plugs were the same , just different colours. if it comes back on the same side you know the issue is in the heater circuit or the wiring harness on the car side. if the error now jumps to the other side you now know you have a bad sensor.

Good Luck ..

 

Thank you guys for all the input, I will definitely try to test the wires if I can find my multimeter.

Another update for today... I think that O2 is the least of my problems at this point, here's why. I mentioned yesterday that my car began misfiring on the way to work and that I turned around to try to get it sorted. Well, after test driving the car yesterday and not finding any problems after it got to operating temps, I decided to drive it today. Big mistake...

Now I've had the flashing check engine light twice and pretty severe misfires while the engine is under load at lower rpms (just before boost picks up). I had to limp it into work at that point and when I got there I scanned it again and pulled the following codes.

P0056 (Heated Oxygen Sensor Heater Control Circuit Bank 2 Sensor 2)
P0161 (Oxygen Sensor Heater Circuit Bank 2 Sensor 2)
P0431 (Warm Up Catalyst Efficiency Below Threshold)
and some new ones....
P0130 (Oxygen Sensor Circuit Bank 1 Sensor 1)
P0300 (Random - Multiple Misfire Detected)

Now, it seems like the random misfire code is kind of a crap shoot, since I am not lucky enough to have a rosstech setup yet to monitor individual cylinders. I guess now the question is, would a faulty pre-cat 02 cause the misfire? I apologize ahead of time if this is common knowledge but I've been reading off and on since the onset of this problem and might have already read about it. I'm off to do more research so that I can get the car back on the road. Lastly, would a either of the ignition control units possibly cause random misfires?

Thanks!

 

Quick update....

I attempted to clean the mass air flow sensor but was thwarted due to the damn anti tamper Torx bit screws. I got one loose with pliers but couldn't get to the one closest to the firewall. Anyway, I replaced a couple suspect hose clamps with no success. I'm going to get some proper bits tomorrow to get the maf sensor off so I can spray it with the cleaning solution. Still no fuel trim lean code yet...

 

Well, I cleaned the MAF sensor and it ran great up and down the mountain. No misfiring at all. In fact, it damn near drove like new. After about 20 minutes of driving, I came back home, with it still driving perfect and let it idle for like 5 minutes in the garage to cool down a bit. Of course, near the end of those five minutes it started running rough and the check engine light started flashing. Back to the old P0300 random misfire with no additional info. The only other code is for the Bank 2 Side 2 O2 heater. It's tough when their are no other codes or specific cylinders...

Anyone know if I may just need a new MAF since cleaning it alone seemed to alleviate the misfire under throttle?

Edit: More specifically, the engine cleared up the misfire on it's own after about 10 seconds and started running smoothly again. Revving the engine slightly also cleared it up causing it to run smoothly again...

 

hot wire MAF sensors are supposed to burn themselves clean before starting or after shutdown, I forget which. Vag-com may be able to check for this.
Do you have stock air cleaner or have you put in an oiled filter type?

Clean the sensor again but look around for what is apparently fouling it….too much oil in crankcase, something leaking into pcv system?

 

Stock air cleaner... I checked it while I was changing the plugs and it still looks fairly new. It's a paper type filter I would guess. I'll look at it again. Last time I checked, oil was filled to the full line a couple days ago. I'll look through the PCV system as well... Thanks for the reply!