Anyone know anything about O2 sensors? Odd problem.

miniyazz

miniyazz

miniyazz

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The Golf has been throwing codes P0160 & P1199. Described as O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2) & O2 Sensor Heater Circ. Electrical Malfunction (Bank 2 Sensor 2).
So, no problem I thought, looks like the heater circuit has gone on the bank 2 post-cat O2 sensor. Anyway before shelling out for a new one I thought I'd look into it slightly further.

I understand when the heater circuits die, their resistance increases. So today I checked the resistance and the B2S2 resistance was only 10.5Ω. I checked the B1S2 resistance which was actually higher at 11.5Ω.

I then thought maybe the wiring to the sensor was dead, but a quick check of the heater wires revealed 12V through them when the engine was running. (While doing this the car threw another code saying B2S2 heater circuit open, which was presumably because it wasn't connected to anything, but confirmed I had the right sensor).

So now I'm a little bit stumped. Does anyone know why I might be getting this code? Is it just that the heater circuit is broken but without increasing the resistance? Should I just buy a new O2 sensor (not particularly cheap, but hardly the end of the world) and give it a try, or perhaps swap over the bank 1 and bank 2 sensors? (I was going to swap over the wires today and see what happened but annoyingly it appears the connectors are designed to be incompatible :mad: - is there a reason for that other than preventing them being confused? They are different colours already!)

Currently I've just plugged both sensors back in and cleared the fault codes in the hope that the connectors were just a bit corroded and will now have a good connection - but I don't know how long I'll have to wait before the fault code reappears and I can put it to bed :(

Cheers for any advice!
 
Have you a good enough voltmeter to check that both post cats are alternating to the same voltage when running? (I'm guessing these are side by side for the 2 banks btw)

Infact cant you swap the 2 post cats and check that the fault moves, therefore identifying the dud? Edit nevermind I've re read above
 
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Hmm probably not - but thinking about it I should be able to check that through OBD - I'll take a look in a few minutes. Cheers
 
Right well I've checked the post-cat sensor on either side and they both remain pretty steady around 0.44V according to the OBD. No significant change with revving the engine either. Now as far as I know, that means both sensors are working correctly - and that the cat is also working fine (and I also had an emissions test done which it passed).

So really I'm stumped as to why I'm getting this code, but I'm increasingly hesitant that it's the O2 sensor at fault :(
 
Brookert said:
Sorry to mention the obvious, but have you checked all cabling for damage?
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I've not traced it all back but have confirmed 12V on the heater circuit, and a new fault code appeared when I unplugged the sensor completely. I suppose I could check it's receiving a reference voltage and such but I think the OBD reading confirmed it's outputting a voltage - which must be reaching the ECU or it wouldn't be showing via OBD.

Thanks for the suggestion though - I suppose if there's an intermittent disruption of signal that didn't show up during my testing it could be due to a dodgy wire. What I may end up doing is either 'making' the connectors fit and swapping the O2 sensor harnesses over, and seeing what happens, or possibly religiously logging the O2 sensor readings and then when the fault code recurs, seeing if there's any odd things going on with the voltage.
 
Brookert said:
Hows your fuel economy? The tell tell sign of a duff O2 sensor is poor fuel economy from what I've experienced.
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I think that may only apply to pre cat sensor. At least on Renaults the post cat is only used to flag up errors and is not used in the feedback loop. I'm not an expert though so other brands could well be different
 
Scooby_WR1 said:
I'd remove the sensors and give them a good clean to see if this helps.
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Cleaning O2 sensors = bad :)

blueseidboy said:
Brookert said:
Hows your fuel economy? The tell tell sign of a duff O2 sensor is poor fuel economy from what I've experienced.
Click to expand...
I think that may only apply to pre cat sensor. At least on Renaults the post cat is only used to flag up errors and is not used in the feedback loop. I'm not an expert though so other brands could well be different
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What he said :)
Post cat only monitors the efficiency of the cat, it's the pre-cat which the ECU uses to adjust air fuel ratio with (and therefore fuel efficiency and other such things). This is partly why it's annoying having a check engine light, the damn things don't do anything useful anyway :p (from my POV!)
 
Ahah, found some old sensor data from apparently anal-retentive data logging.
O2%20sensors.png


Looks like B1S2 varies quite a bit once warmed up, with an average of ~0.6V, while B2S2 sits around 0.44 throughout with just a few random spikes (remember, this was over a 40min journey). I wonder if the code is because B2S2 isn't changing enough and may therefore be dying?
 
blueseidboy said:
I think that may only apply to pre cat sensor. At least on Renaults the post cat is only used to flag up errors and is not used in the feedback loop. I'm not an expert though so other brands could well be different
Click to expand...

Well I've learned something very useful today! I was wondering which sensor was responsible for what, might see about replacing mine as it gives an intermittant fault, and my fuel economy isn't as it should be.
 
If those two sensors are on different manifold / cat branches at exactly the same location then something certainly looks odd with that data. Dos the mk4 vr6 have 2 cats? If so it would explain why these two post cat sensors are there, the only thing ringing slight alarm bells for me is that the connections are different - this suggests the sensors might not be doing the same job and therefore may not show the same on/off pattern.
 
I think it's a twin cat - kinda two-in-one. The sensors are at the same point on each of the post-cat branches. I wish I knew why the connectors are different! Could be perfectly innocent, or not. They are very similar - they are the same, but have plastic tags added on in slightly different places to stop them from fitting.
 
It may well just be some clever thinking by vw to ensure the correct sensor is reading back to the correct monitor - I had a look at a couple of replacement cats for the car and as you say its a twin setup located at the same point. The readings suggest that you need either a new o2 sensor or cat, make sure to get a known good one though as cheap o2 sensors can cause their own problems
 
rodenal said:
It may well just be some clever thinking by vw to ensure the correct sensor is reading back to the correct monitor - I had a look at a couple of replacement cats for the car and as you say its a twin setup located at the same point. The readings suggest that you need either a new o2 sensor or cat, make sure to get a known good one though as cheap o2 sensors can cause their own problems
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Lol :D

Just bought a cheap one off ebay about 8 minutes before you posted, haha. Still nearly £30 but a lot cheaper than the nearest at around £80! Oh well we shall see.

Thanks for all the help guys!
 
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