post cat o2 sensor keeps failing

   #1  

v-8-q

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2002 allroad, not chipped or modified.
Like the title says, I replace bank 1 sensor 2 (post cat) with a new sensor and the heater fails within a few hundred miles. All the sensors are bosch, some were universal, some were exact fit bosch aftermarket, some were real OEM (but used). All fail the same way.
All failures can be verified with an ohm meter - the heater is open.
Actually both sides were doing the same thing when I first got the car, and both o2 sensor bungs had been hacked out and badly welded replacements put back in, apparently by a drunk monkey. There were lots of places where exhaust was obviously leaking. Replacing the bung and getting the exhaust pipe coupler/clamps seems to have cured the bank 2 side, but bank one still eats up sensors about as fast as I can put them in there.
Other things I have done:
* 12v has been verified.
* The ECU is working properly. I can put a light bulb in the circuit and it switches on and off, as well as making the code go away. I did actually go so far as to replace the driver chip in the ECU. It made no difference.
* I can not see/find any other exhaust leaks, and the car seems to run fine.

I am at a total loss as to what to try next. Any help would be greatly appreciated!

thanks
Dave
 
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Jack@European_Parts

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As per EPA regulations it is advised to install genuine approved cats with down pipes and new factory OXS sensors.

Then you won't have such an issue.........if fuel PSI and trims are correct.
 
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v-8-q

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this is all factory oem parts. The cats appear to be working too - the post cat sensors are out of phase with the upstream. There is no sign of them being tampered with, and I have no intention of doing that either. Fuel trims also look OK - at least to me. I am definitely a newbie at this though.
I think the reason the bungs were replaced was rust. This was an Oregon car and it gets wet there...
Also, whoever was working on it was not the most competent fella around. I have no idea who it was but everywhere he has been there are stripped out torx screw heads and everything is way over tightened. As in transmission oil pan screws needing a breaker bar to get out, and several needing to be chiseled out. Not due to rust or corrosion - just way too tight.

I will get the Auto-Scan that Jef asked for soon. maybe that will shed a little light on something.

And just an FYI - I am not a professional mechanic so you can expect some goofy questions now and then...
I do have some electronics background though, and used to work on multi-million dollar machines so I am well prepared for an allroad!
My previous and all time favorite car was a 1991 Audi V8 Quattro 5-speed. I would still be driving it today except it got totaled out while parked in front of my house.
I managed to keep it running well though for about 17 years, thanks in large part to help from a good local Audi shop. (btw I am using the same O2 sensors they do with no troubles at all)
 
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Jack@European_Parts

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actually both sides were doing the same thing when i first got the car, and both o2 sensor bungs had been hacked out and badly welded replacements put back in, apparently by a drunk monkey.


FOD written record says otherwise!



Oh an FYI........ the pre and post cats are all together on one pipe for each bank, as one replacement part per side...........so double FOD.
 
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   #6  

v-8-q

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OK here is the scan. it is from a few months ago but the codes are the same.

Code:
Monday,23,November,2015,19:07:03:53843
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 8.1 x64
VCDS Version: 15.7.1.0 (x64)
Data version: 20150904
www.Ross-Tech.com


VIN: WA1YD64B22N000000   License Plate: 
Mileage: 118335   Repair Order: 



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 4B (4B - Audi A6/S6/RS6/allroad C5 (1998 > 2006))
Scan: 01 02 03 06 08 15 16 17 18 22 34 35 36 37 45 55 56 57 65 67
          75 76 77
 
VIN: WA1YD64B22N098177   
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 078-907-551-AZA.lbl
   Part No: 4Z7 907 551 M
   Component: 2.7l V6/5VT     G   0001  
   Coding: 06752
   Shop #: WSC 02325  
   VCID: 4D91253A87034D56E6-5140
   WA1YD64B22N098177     AUZ7Z0A2034970

3 Faults Found:
17866 - Exhaust Gas Temp Sensor 2 (G236) 
            P1458 - 35-10 - Short to Ground - Intermittent
17526 - Oxygen (Lambda) Sensor Heating; B1 S2 
            P1118 - 35-10 - Open Circuit - Intermittent
17522 - Oxygen (Lambda) Sensor; B1 S2 
            P1114 - 35-10 - Internal Resistance too High - Intermittent
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 02: Auto Trans        Labels: 01V-927-156.lbl
   Part No: 4Z7 927 156 F
   Component: AG5 01V 2.7l5VT USA 1818  
   Coding: 01002
   Shop #: WSC 02325  
   VCID: 4999112A736B5176CA-515E

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8D0-907-389.lbl
   Part No: 4Z7 907 389 A
   Component: ABS/ESP allrad      D55  
   Coding: 06497
   Shop #: WSC 00000  
   VCID: 4A9B2E26766D5A6EC3-5140

1 Fault Found:
01119 - Gear Recognition Signal 
            35-10 -  -  - Intermittent

-------------------------------------------------------------------------------
Address 06: Seat Mem. Pass        Labels: None
   Part No: 4B0 959 760 C
   Component: Sitzmemory R1 BF    0103  
   Coding: 00003
   Shop #: WSC 00000  
   VCID: 2D5145BAE7C36D56C6-4B1A

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 4B0-820-043-MY2.lbl
   Part No: 4B0 820 043 AD
   Component: A6-Klimavollautomat 0105  
   Coding: 00010
   Shop #: WSC 02325  
   VCID: 5CB7D87ECCF9D4DE61-2580

1 Fault Found:
00796 - Fan for Interior Temp Sensor (V42) 
            42-10 - Speed Deviation too High - Intermittent

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 4B0-959-655-AI84.lbl
   Part No: 4Z7 959 655 E
   Component: Airbag 8.4E         4000  
   Coding: 0000307
   Shop #: WSC 02325 785 00200
   VCID: 51A9394ACB3B69B682-515E

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel        Labels: 4B0-907-487.lbl
   Part No: 4B0 907 487 H
   Component: Lenkradelektronik   D01   
   Coding: 01012
   Shop #: WSC 02325  
   VCID: 316959CAFBFB09B6E2-5210

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 4B0-920-xxx-17.lbl
   Part No: 4B0 920 981 P
   Component: KOMBI+WEGFAHRS. VDO D09  
   Coding: 06264
   Shop #: WSC 23190  
   VCID: 336553C201E73BA690-5140
   WA1YD64B22N098177     AUZ7Z0A2034970

1 Fault Found:
01325 - Control Module for Tire Pressure Monitoring (J502) 
            49-10 - No Communications - Intermittent

-------------------------------------------------------------------------------
Address 34: Level Control        Labels: 4Z7-907-553.lbl
   Part No: 4Z7 907 553 E
   Component:  - 2C1A1          D040    
   Coding: 25500
   Shop #: WSC 26097  
   VCID: 479D1712657FA706DC-5140

1 Fault Found:
01772 - Signal from Level Control Pressure Sensor (G291) 
            27-10 - Implausible Signal - Intermittent

-------------------------------------------------------------------------------
Address 35: Centr. Locks        Labels: 4B0-962-258.lbl
   Part No: 4B0 962 258 J
   Component: Central Lock/Alarm  D35  
   Coding: 15885
   Shop #: WSC 02325  
   VCID: 306F5CCEF0F100BEED-4F04

1 Fault Found:
01370 - Alarm triggered by Interior Monitoring 
            35-00 -  - 

-------------------------------------------------------------------------------
Address 36: Seat Mem. Drvr        Labels: None
   Part No: 4B0 959 760 B
   Component: Sitzmemory R1 F     0102  
   Coding: 00001
   Shop #: WSC 00000  
   VCID: 2C5748BEDCD9645ED1-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 45: Inter. Monitor        Labels: 4B0-951-178.lbl
   Part No: 4B0 951 178 A
   Component: Innenraumueberw.    D04  
   Coding: 00102
   Shop #: WSC 02325  
   VCID: 2643BA96C2355E0E07-517C

No fault code found.

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 4Z7-907-357.lbl
   Part No: 4Z7 907 357 
   Component: dynamische LWR       D07  
   Coding: 00030
   Shop #: WSC 02325  
   VCID: 0407C01E14C94C1E79-4B64

No fault code found.

-------------------------------------------------------------------------------
Address 56: Radio        Labels: 8E0-035-1xx-56.lbl
   Part No: 4B0 035 195 J
   Component: symphony II NP2    0008   
   Coding: 00205
   Shop #: WSC 00000  
   VCID: 275DB792C53F47063C-4EB2

No fault code found.

-------------------------------------------------------------------------------
Address 65: Tire Pressure        Labels: 4D0-907-273.lbl
   Part No: 4D0 907 273 A
   Component: Reifendruckueberw.  D110   
   Coding: 22307
   Shop #: WSC 23352  
   VCID: 2541BD9ABF3355160E-515E

No fault code found.

-------------------------------------------------------------------------------
Address 76: Park Assist        Labels: 8Z0-919-283.lbl
   Part No: 8Z0 919 283 
   Component: Parkingsyst. A6 RDW D08  
   Coding: 01186
   Shop #: WSC 02325  
   VCID: 020BC6060EDD422E4B-515E

No fault code found.

End-------------------------(Elapsed Time: 04:35)--------------------------
 
   #7  

v-8-q

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Yes - I know the whole cat assembly is one giant expensive piece. No doubt why the previous owner had this repair done.
But - what is FOD?
(told you I was a newbie)
 
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NZDubNurd

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I'm no o2 sensor expert, but are you buying the o2 sensors that are "correct" for the CAR, or are they replacements for what was IN the car ALREADY?

Wasn't it Jef, who ust posted a tale of woe about a situation like that?
 
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Jack@European_Parts

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Highlight captions........with cursor.

FOD = https://en.wikipedia.org/wiki/Foreign_object_damage


https://www.google.com/imgres?imgur...d=0ahUKEwiQvMj4-P7KAhVGXD4KHSHXBHQQMwg6KAQwBA


Sounds like the parts and repairs are incompatible.........


Just an FYI .......the driver for the Heated OXS share the circuit for all 4 OXS sensors ( internal to the controller ).........which means you could have a fault in a forward sensor or effect how DTC's are reported......... if mixing and matching FOD parts.

Further .........code such as below tells me your OXS BUNG HOLE, is in its wrong area or placing the sensor in such a manner, to collect this thing called H20/CO/C02/N elements, which combined has this amazing property of super conductivity..........when surrounded by other rare metals.

17522 - Oxygen (Lambda) Sensor; B1 S2
P1114 - 35-10 - Internal Resistance too High - Intermittent


 
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   #10  

Jef

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What we tend to get calls about with non factory cat repairs is the car will have cat codes four or five days later because the aftermarket cats don't have a large enough core, they run out of oxygen.

Now a car eating O2 sensors is a new one to me. Sure, O2 sensors can go bad here and there, but it gets replaced and that is it. How much to factory design is the exhaust? Vibration issues somehow?

As for your source of O2 sensors... parts are not all the same. I suspect there is a 3rd shift B-team that makes parts and these are the "OE" discounted parts some places sell.... sure, they look the same, but the level of quality just isn't the same. I won't name names...
 
   #11  

Jack@European_Parts

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If you would be so kind and reset your DTC's and repost a complete auto-scan........

I'd like to see something..........Unedited Please......


Monday,23,November,2015,19:07:03:53843
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 8.1 x64
VCDS Version: 15.7.1.0 (x64)
Data version: 20150904
www.Ross-Tech.com


VIN: WA1YD64B22N000000 License Plate:
Mileage: 118335 Repair Order:



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 4B (4B - Audi A6/S6/RS6/allroad C5 (1998 > 2006))
Scan: 01 02 03 06 08 15 16 17 18 22 34 35 36 37 45 55 56 57 65 67
75 76 77

VIN: WA1YD64B22N098177
-------------------------------------------------------------------------------
Address 01: Engine Labels: 078-907-551-AZA.lbl
Part No: 4Z7 907 551 M
Component: 2.7l V6/5VT G 0001
Coding: 06752
Shop #: WSC 02325
VCID: 4D91253A87034D56E6-5140
WA1YD64B22N098177 AUZ7Z0A2034970

3 Faults Found:
17866 - Exhaust Gas Temp Sensor 2 (G236)
P1458 - 35-10 - Short to Ground - Intermittent
17526 - Oxygen (Lambda) Sensor Heating; B1 S2
P1118 - 35-10 - Open Circuit - Intermittent
17522 - Oxygen (Lambda) Sensor; B1 S2
P1114 - 35-10 - Internal Resistance too High - Intermittent
Readiness: 0000 0000
 
   #12  

v-8-q

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What we tend to get calls about with non factory cat repairs is the car will have cat codes four or five days later because the aftermarket cats don't have a large enough core, they run out of oxygen.

Now a car eating O2 sensors is a new one to me. Sure, O2 sensors can go bad here and there, but it gets replaced and that is it. How much to factory design is the exhaust? Vibration issues somehow?

As for your source of O2 sensors... parts are not all the same. I suspect there is a 3rd shift B-team that makes parts and these are the "OE" discounted parts some places sell.... sure, they look the same, but the level of quality just isn't the same. I won't name names...

here is what I know -
I bought this car from the second owner, and he bought it with very low miles, driving it up to about 115K miles. In that time he used the dealer for all repairs at first, then moved on to some second rate shop (btw I hate do disparage any one person or shop - but this guy should not own a wrench) as the dealer prices started to eat him alive. He is a very well off doctor too, so the car got whatever it needed - including a new (actually used) transmission.
When I bought it, the check engine light was on, and he had a cheapo scan tool that could reset the light as needed. He disclosed everything to me, and is actually a really nice guy.The rear O2 sensors were both OEM but you could tell someone had a very hard time removing them at one point. This is probably where the bungs got damaged, and the reason for removing them was probably to remove the transmission.
Beside the leaking and badly welded bungs, the two exhaust pipe clamp/couplers were leaking, and this is just a few inches downstream from the sensors. Again probably from the transmission job.
I replaced both (rear) sensors with Bosch universals, and they both burned out within a few hundred miles. I had the left side bung replaced (the right seemed not to be leaking to me) and fixed the pipe clamps and installed a new set of universals. The left one is still OK after a few thousand miles. The right one has been through several universal as well as direct replacement sensors. They have all burned out the heater. I then installed several used sensors - from similar Audis and even a Ford (which still uses a Bosch sensor) with the same results - the heaters all burn out. I have also now replaced the right bung however it is right at the outlet of the cat.
(btw, ford four wire sensors worked great in my '91 V8 Quattro which required a three wire from the factory)
I know enough about electricity to understand how the heaters work. According to Bosch (I called them) the heater is a positive coefficient RTD (restive thermal device). This means that as the temperature goes up, so does the resistance, and therefore the current goes down. It is self regulating with respect to the amount of current it can draw. I actually verified this with a ammeter (current meter) and a torch. Current goes down as temperature goes up.
So - the only piece I could think of to look at next was wiring and ECU. The 12v supply to the sensor can easily carry 2 amps of current. No bad connections there. The negative side of the heater goes into the ECU. This wire can also easily carry 2 amps of current from the ECU pin to the sensor connector. No bad connections here either. So that left the driver chip in the ECU. I replaced the chip (not a job for the faint hearted btw) and still sensors burn out. I can see the output switching on and off by installing a light bulb on the heater wires at the O2 sensor connector, I am confident the ECU is working.
And again, there is no sign of physical damage to the exhaust system, it is all OEM including the downpipes and cats, and this all started with OEM sensors.

SO now - where to go next? I don't know how to interpret fuel trims yet but they seem OK. It seems like a upstream air leak would show up here and affect both sides. I can see no exhaust leak from the turbo to the muffler coupler (verified by the muffler shop that installed the new bung). I can see no electrical reason the sensors would burn out.
My next move is to install yet another used (I can't keep throwing new sensors at this) sensor installed in one of those spark plug spacers to remove it from the exhaust stream. I am all ears for any suggestions you all may have.

Oh, I wanted to add, while I am not a mechanic, I have a very good relationship with the only "Audi only" shop in town. They love to bounce ideas back and forth and to help me in general. They are as stumped as I am on this one.
And, my parts guy is also top notch. He knows and has worked with Febi Bilstein (the person) and supplies only good proven parts. The whole valley uses the same stuff I am and they have no problems. As to your point about "OE" parts, he likes to say that "Febi makes boxes", meaning you never know who made what is inside. It might be actual OEM, it might be chinese crap. Usually it is somewhere in the middle.
 
   #13  

jyoung8607

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If the hacked-up bung is badly positioned or installed (and it sure sounds like it is) the ECU might have to run the heater a lot more than usual, shortening its life. The bung might leave the sensor positioned too far out of the exhaust stream, or admit cold air around it, or make physical contact with the sensor tip somehow and act as a heat sink/wick.

Jason
 
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Jack@European_Parts

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Now that the 3rd Testament has been written........

Please clear codes and post a new auto-scan unedited sir........

Please post the heater block values during basic settings test at 3k rpm or higher 0x01-04-041/042 logged.........
 
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   #15  

Zenerdiode

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Here's my $0.02 worth - The heaters heat up to a cherry red hot - and being the aft ones are designed to run in very little amounts of oxygen. You've metioned exhaust leaks, even the ones downstream can get to the sensors because the pulsing nature of the exhaust creates momentary vacuum that will suck fresh air in. In the presence of fresh air, the sensors may oxidise and burn up more quickly than in the designed near zero oxygen gas stream.
 
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v-8-q

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Highlight captions........with cursor.

Just an FYI .......the driver for the Heated OXS share the circuit for all 4 OXS sensors ( internal to the controller ).........which means you could have a fault in a forward sensor or effect how DTC's are reported......... if mixing and matching FOD parts.

Further .........code such as below tells me your OXS BUNG HOLE, is in its wrong area or placing the sensor in such a manner, to collect this thing called H20/CO/C02/N elements, which combined has this amazing property of super conductivity..........when surrounded by other rare metals.

Just thought I would mention, the four oxygen sensors all have an independent driver on this car. I have traced all wires to the driver chips. The front two sensors have what appear to be a dedicated driver IC in a TO220 like case (for high current and good heat transfer). I don't have a part number or image for it.
The rear are driven by this chip:
http://www.ebay.com/itm/DRIVER-BOSC...SCH-MERCEDES-TOYOTA-AUDI-VW-ECC-/291088770548
and each one gets an independent channel.
I don't remember now if they all share the same fuse, but I think they do.

I think you are on to something with the sensor placement. I wish I knew what it looked like before the fella with the hot wrench got ahold of it. There isn't much else it could be.
 
   #17  

v-8-q

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Here's my $0.02 worth - The heaters heat up to a cherry red hot - and being the aft ones are designed to run in very little amounts of oxygen. You've metioned exhaust leaks, even the ones downstream can get to the sensors because the pulsing nature of the exhaust creates momentary vacuum that will suck fresh air in. In the presence of fresh air, the sensors may oxidise and burn up more quickly than in the designed near zero oxygen gas stream.

I definitely agree with this. The left side was cured after all exhaust leaks around the bung and pipe coupler were fixed. The stumper for me is I just can not find a leak anywhere.

as a side note, Newcastle Brown Ale is one of my favorites. Is this the same Newcastle you live in?
 
   #19  

Jack@European_Parts

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Just thought I would mention, the four oxygen sensors all have an independent driver on this car. I have traced all wires to the driver chips. The front two sensors have what appear to be a dedicated driver IC in a TO220 like case (for high current and good heat transfer). I don't have a part number or image for it.
The rear are driven by this chip:
http://www.ebay.com/itm/DRIVER-BOSCH...-/291088770548
and each one gets an independent channel.
I don't remember now if they all share the same fuse, but I think they do.

I think you are on to something with the sensor placement. I wish I knew what it looked like before the fella with the hot wrench got ahold of it. There isn't much else it could be.

I suggest anyone/you take a resistor, and add to the front or back on either bank heater ECU side; see how it effects the actual heater resistance values displayed by the controller in blocks.

Any word on the new auto-scan, after an immediate clear of DTC's and the block value tests logged?
 
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jyoung8607

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Here's my $0.02 worth - The heaters heat up to a cherry red hot - and being the aft ones are designed to run in very little amounts of oxygen. You've metioned exhaust leaks, even the ones downstream can get to the sensors because the pulsing nature of the exhaust creates momentary vacuum that will suck fresh air in. In the presence of fresh air, the sensors may oxidise and burn up more quickly than in the designed near zero oxygen gas stream.
I like this. :thumbs:
 
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