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Discussion Starter #1 (Edited)
I recently replaced the front pipe (also called an "intermediate" pipe or flex pipe) on my 1.8T exhaust. To do that I had to remove the catalytic converter. While I had it out I thought it would be a good time to recoat the o2 sensors with antiseize since they're the original sensors 15+ years old, and I figured I'd probably have to replace one or the other soon. They wouldn't budge until I heated them up with a propane torch and even then I had to tap the o2 offset socket tool with a mini-sledge to get removal started. I coated the threads with nickel antiseize and reinstalled, and then reinstalled the cat.

Since then I get P0130 DTC that reappears when I clear it:

16514 - Oxygen (Lambda) Sensor B1 S1
P0130 - 008 - Malfunction in Circuit - MIL ON

It's certainly possible that I damaged either O2 sensor. I do not know what testing I should do. I don't own the Bentley for the VW B5.5 so I used an older Audi B5 manual that I found online and I hope is similar, 24-71 Oxygen sensor control checking.pdf. So far I've checked the heater resistance which is within range, and I've used VCDS to monitor some lambda values but really I don't understand what I'm looking at. Does anyone understand these values? What would you check in this situation? Do our O2 sensors have an external port for ambient air? Can they be measured like normal O2 sensors like some DIYs I've read?

Here's a screenshot from idle in park, no acceleration, with P0130 set:



Here's a screenshot from running 2400 rpm in park, with P0130 set:
https://www.dropbox.com/s/eql5mbc0r3ecj1i/vcds_o2_b1s1_2400rpm_p0130.jpg?raw=1

Here's a screenshot from idle in park, no acceleration, right after I cleared P0130:
https://www.dropbox.com/s/2nbdy64bhgcb7kd/vcds_o2_b1s1_idle_dtc_cleared.jpg?raw=1
 

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It would be my guess seeing that this problem showed up right after using a torch on the o2 sensors, some kind of damage was done inside the ceramic portion of the sensor. Yes the temperature of the sensor gets to be well over 500 Celsius (in excess of 900 F) but that's only at the probe protruding into the cat.

I can't remember what the values are, I don't have my VCDS or a Bentley right now, but there is a voltage range and a minimum cat temp that are requirements for proper operating conditions.
That third reading of cat temperature in group 034 bank 1 sensor 1 seems awfully low.
On the V6 engines, if you do a complete engine readiness test, (takes about 15-20 minutes) the testing portion of the o2 sensors clearly shows the range it supposed to be within.
In my own experience, if the o2 sensor portion of the test fails, the specified o2 sensor is faulty. Only one time I can remember the sensor portion of the test failed but the o2 sensor was not at fault. The connections to a universal o2 sensor were culprit.

I would first clear the codes and see if they come back.
If they do... try running the complete engine readiness test to see which one (or both) fails and replace the sensor as noted by failure.

Shop around for sensors, there are huge price differences on these things, I personally would stick with NGK, Denso or Bosch. I would also recommend the sensors with the OEM connector (original colored connector) instead of the universal sensor. Yes the universal sensor is by far cheaper, but they have those splice connection block thingys that sometimes prove to be bothersome. As in connection issues picked up by VCDS.

Hope I am of some help anyways.
 
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The O2 sensor usually should be replaced every 100K miles. If yours had sit there for 15 years then it's way past its change due time. Even if you hadn't got fault codes with it, it certainly had internal wear and wouldn't function as optimal. Thus, instead of spending time to diagnose and test a very old senor, wouldn't it better to get a new one and replace it? You'll end up doing that any way.

This is a very critical component. So don't buy a cheap aftermarket one. Bosch or OEM should be good and they cost around $80. Anything cheaper is suspicious.
 

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Discussion Starter #4
Thanks guys. I replaced the upstream O2 sensor with a Walker model 250-25004 that I bought off eBay for $50 and that fixed it. I couldn't bring myself to spend $100 with all the money I've been putting in this car recently (more on the way too I got a busted cv boot, it never ends).

If anyone is curious the Walker sensor has more holes than the OEM sensor:



After I installed the new sensor I cleared the P0130 DTC and idled the car and checked the O2 sensors' status in VCDS (group 030). B1S1 showed as ready and active, unlike the old sensor which showed neither. Specifically here is a legend for both sensors and what they showed before and after if it's any help to anyone:

B1S1 (Upstream sensor):
1xxxx = Lambda Sensor Control Cyl. 1 active
x1xxx = Catalytic Converter Venting active
xx1xx = Lambda Sensor Heating on
xxx1x = Lambda Sensor ready
xxxx1 = Lambda Control active

Old B1S1 showed 00100 or 00000 at idle. The heating bit turned on and off extremely fast like a flicker.
New B1S1 showed 00111 or 00011 at idle. The heating bit turned on and off but at the same consistency as B1S2.
I don't know why the difference in the heating cycles. I did check the resistance of the heater on the old sensor and it passed and was within range (4.9 ohms).

B1S2 (Downstream sensor):
1xxx = Lambda Control (P-Portion) active
x1xx = Lambda Sensor Heating on
xx1x = Lambda Sensor ready
xxx1 = Lambda Control (I-Portion) active

B1S2 showed 0110 or 0010 with the old B1S1 sensor. With the new B1S1 sensor I didn't really pay attention to B1S2 but I did note when I was at 2400 rpm in park (to warm things up) it showed 1110.

After driving the car for 50+ miles VCDS showed B1S1 OK:




I did the O2 control checking tests from the Audi manual and they pass now. (Note there's a typo in the manual for the O2 control checking where it says on page 24-75 that the display group for O2 adaptation values is 36 but it's actually 32.)

My emissions readiness is almost complete but the secondary air system is either failing or incomplete, not sure why.



I did try a secondary air injection test (group 077, basic settings) and it says "System Not OK" however the check engine light isn't on. I'm not sure if it says that because something is actually wrong or maybe one trip of 50+ miles is not enough information for the system to judge secondary air. Unfortunately the Audi test for the secondary air system looks like it requires specialized tools. I'm going to wait a few more trips and hope it resolves itself before looking into it again.
 

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The next cold start will probably resolve the SAIP not ready.

SAIP only operates when engine temperature is between 32 and 90 F (from memory, maybe not exact) at startup.

If the SAIP operates (for 60 or 100 seconds, depending on engine), then it waits until the engine is warmed up and at idle, then it runs the SAIP again for just a few seconds. (Mine usually tests at the stop sign 1/2 mile from my house; 1.8T warms up quickly.) During that few seconds, the ECM watches for a large increase in the O[SUP]2[/SUP] reading from the upstream sensor. If it sees it, it's a pass.

So, it's really a thorough test of all the hardware. The SAIP has to blow air, no leaks, and the combi valve has to open (via vacuum solenoid valve), and the O[SUP]2[/SUP] sensor has to work!

Here's hoping you get readiness. Be sure you do a cold start in the morning, when the weather is cool, and pause briefly once the engine is warmed up so the test can run. Be thankful you don't live in Phoenix...
 

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I normally don't believe in replacing a part without confirmation of a defect in it, but I am going to replace both front O2 sensors on my 1996 A4 before I have it smog tested this year. They are 23 years old and have been subjected to 111K miles of probably 70 or 80 percent city "driving from hell."
 

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I normally don't believe in replacing a part without confirmation of a defect in it
So true.

When I lived in WI, whenever any of my Passat's were due up for the emissions test (every other year in WI) I would hook up VCDS and do a complete adaptation test. If any portion of it failed, it was surely going to fail the test mandated by the state.
It was rock solid insurance against failed trips to the DMV.

VCDS didn't save me from the idiots at the testing facility though. One of the last tests I had their before moving to AZ, the girl in the shop said my car didn't have an OBDII port. :icon_eek:

After the state of WI closed down all of their testing facilities and turned it over to third party testing,
I became a repeat customer at a garage that was state certified for testing. At the time I had 3 Passat's out on the road and I'd go in for the test, the guy at the counter being savvy to the all to common CEL's, would ask me, "think it'll pass this time?". I always responded with an almost arrogant, Yes of course it will. :D
 

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Discussion Starter #8
My emissions readiness is almost complete but the secondary air system is either failing or incomplete, not sure why.
The secondary air system status did not resolve on the next start but I drove it around for almost 2 weeks and now it shows as passing. So if anyone else runs into this it will probably take more than a day and less than 2 weeks :)
 

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Yeah, I've noticed that since I have a huge hole in my SAIP-to-combi valve hose. The CEL would only come on about every 2 or three cold starts. I guess it compares a few starts to determine what values it is seeing are a fluke or not.
 

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Discussion Starter #10
(TLDR: Buy the Bosch, not the Walker.)

The Walker 250-25004 O2 sensor lasted a little more than a year. I replaced it with with Bosch 17351 which appears to be an OEM part since it has a VW part # etched on it. I tightened to 35 ft-lbs.

I took some measurements of both the old Walker and the new Bosch, maybe it will be useful to someone else.

Ohms measurements, Walker sensor, not working:
Pin 1 & 5 measure 0.2 ohms. Beeps. (Second measurement: 0.8 ohms)
Pin 2 & 6 measure 133 ohms. Does not beep.
Pin 3 & 4 nothing. Does not beep. Audi 24-71 says it should be between 2.5 and 10 ohms.

Ohms measurements, Bosch sensor, working:
Pin 1 & 5 nothing. Does not beep.
Pin 2 & 6 measure 107 ohms. Does not beep.
Pin 3 & 4 measure 3.1 ohms. Beeps.

The Bosch connector does not have the pins numbered. With the only round side of the connector on the right, the male pins are ordered like this:
135
246

Beeping just means my tester beeps for continuity when resistance is low enough.

O2 status after 10 min - B1S1 bad - Walker: (animated graphic)
101041


O2 status after 10 min - B1S1 good - Bosch: (animated graphic)
101042


O2 advanced values after 20 min - B1S1 bad - Walker: (animated graphic)
101043


O2 advanced values after 20 min - B1S1 good - Bosch: (animated graphic)
101044


O2 measuring blocks after 30 min - B1S1 bad - Walker:
101045


O2 measuring blocks after 40 min - B1S1 good - Bosch:
101046
 

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Very nice and thorough! I am always one to research a part to death in order to use the lowest cost brand while ensuring I'll have some kind of reliability. I have never been able to find one as consistent and accurate in operation as a Bosch sensor for the O2s. Then, I just scour the webs for the lowest cost Bosch. I got my 17351 for something like $45, I think. Works great.
 

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Discussion Starter #12
I usually go aftermarket but sometimes I'll go OEM for important things like when I bought a Bosch knock sensor. When I do the timing belt I'll probably go conti-tech germany because that's what my original belt is. For the Walker O2 I gambled and lost, so back to OEM. Also the Walker has only a 90-day warranty. If anyone is concerned about their part warranty they should look into FCP Euro which has lifetime replacement on any part they sell even though you may pay more for the part upfront. This time I ordered from Amazon though.
 
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