# O2 Sensor Voltage (225 1.8T)



## maccos (Oct 18, 2009)

Just got a vag com and have replaced my front O2 sensor the other week because I suspected it was on its way out due to some fault codes. 
I ran the block to check the voltage of both front and rear sensors. While driving the rear O2 sensor reads in a consistent manner, between .3-.6 volts most of the time, but the front O2 sensor is all over the board, when idling it jumps anywhere from 0-.7 volts up down up down, etc, never a steady line, same when cruising, or accelerating, its just up down up down up down, is this normal?


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## bearthebruce (Dec 23, 2005)

*Re: O2 Sensor Voltage (maccos)*

yes, this is pretty normal behavior. The front sensor is looking at the untreated exhaust which contains all the components of the combustion. The rear sensor is seeing the output of the Catalytic converter which cleans up and removes many of the components. The oxygen content at the back of the cat will be relatively constant if the cat is doing its job.


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (bearthebruce)*

I dont understand how this would be useful information for the ECU, it is telling the ECU its lean, rich, lean, rich, lean, rich, never consistent. I assume the ECU is ignoring it and going off a predetermined map. 
I am also not getting a resistance reading on the front O2 Sensor, but am getting one on the rear.
If I look at the readiness under engine, oxygen sensor(s) read "failed or incomplete".
The trim value for multiplicative trim is about 15%, additive trim is near zero. 
All I have is an APR 93 octane flash and I feel like Im not making full power, which is annoying to spend $500 and not get the full benefits.
Any thoughts on this info?


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (maccos)*

Ok, so the readiness of O2 sensors are good now...
I logged a VAG COM torque run with MAF plugged and unplugged
I got a torque of 205 ft*lb, which equates to 180 HP
according to APR I should be at 260tq/hp
Not sure if vag com is all that accurate to test these values. 
I also noticed that while the MAF was unplugged, the voltage reading on the front O2 sensor was much more consistent while idling, but off idle is is all over the place.


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## Dana @ Ross-Tech (Sep 15, 2009)

*Re: O2 Sensor Voltage (maccos)*


_Quote, originally posted by *maccos* »_I dont understand how this would be useful information for the ECU, it is telling the ECU its lean, rich, lean, rich, lean, rich, never consistent. I assume the ECU is ignoring it and going off a predetermined map. 

This is normal.The Ecm does not ignore the O2s readings.

_Quote, originally posted by *maccos* »_
The trim value for multiplicative trim is about 15%, additive trim is near zero.

See this:
http://wiki.ross-tech.com/index.php/Fuel_Trim_Info
What faults were present before the O2s replacement? Post the scan data if you have it.


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (Dana @ Ross-Tech)*

The faults I had were:
Internal resistance too high, O2 sensor 1
Lean condition detected by oxygen sensor 1
incorrect flow of sais detected
Car was going in and out of limp mode, my guess b/c of the lean conditions. 
Also my gas mileage is fluxuating between 24-31 mpg while highway driving, it should be near 31.
Hasn't gone into limp mode for awile but the 15% trim seems high to me. I unplugged Maf and the car didnt seem to respond much differently. 
I will try running a log and see what kind of airflow im getting thru the maf, how do I increase the sample rate when logging, im only getting about 3/s, there is no turbo button that ive seen on ross tech site, I just downloaded the latest version.


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## vwemporium (May 27, 2002)

*Re: O2 Sensor Voltage (maccos)*

Listen to me.
Unplugging the air-mass is not the correct thing here.
Replace the air-mass its bad or supply voltage etc or there is a faulty harness or ecu.
The air mass if bad will cause the lean condition and the sporadic condition.
The OXS may come around but may also have to be changed.
CAT may also have been damaged.
What is your CAT amplitude in 01-04-046 field 3.
Use a factory part/Bosch or you will be sorry.
Best,
Jack


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (vwemporium)*

Did a log of the MAF sensor, got pretty consistent readings between, 170-175 at 5600 RPM, from what I've read this confirms that the MAF sensor is good, yes? Climbs in a linear fashion too.
Also did a few logs on boost pressure and got a consistent peak of about 14.5 PSI, and settling down to 12-13 PSI, seems low to me, right, for an APR 93 oct flash??
Block 46 Cat Diagnostics for Amplitude Ratio shows up as nothing in that feild, its blank!
What next??


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## vwemporium (May 27, 2002)

*Re: O2 Sensor Voltage (maccos)*

You have to run the test.
01-04-046 after car at temp and exhaust temp above 460C
Oh well I guess you know how to log but not how to do readiness tests.
HMMMMMMMMMMMMMMMm
And the walk in a circle continues.







cool

Best,
Jack


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (vwemporium)*

Any info on the readiness test for the Cat? Not sure about that, Im just learing VAG COM throught trial and error.
Logged actual boost vs requested boost, requested boost is usually about 2 PSI more than actual, making it about 17 PSI boost max requested. 
More importantly the fuel trim is now up to 22%, and shows a soft code of system too lean - intermittent. Any other clues as to what to check to solve this lean condition? What sensor judges that the system is too lean, front O2 Sensor I would guess?
Thanks for any help again


_Modified by maccos at 3:34 PM 12/15/2009_


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## Dana @ Ross-Tech (Sep 15, 2009)

*Re: O2 Sensor Voltage (maccos)*

MAF. This is why I asked for scan data from before parts replacement.
http://wiki.ross-tech.com/index.php/Fuel_Trim_Info
Please post the new scan, with current faults.


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (Dana @ Ross-Tech)*

Dana,
Before I replaced the O2 sensor the codes that came up were:
Internal resistance too high in O2 sensor 1
Lean condition bank 1 sensor 1 
Incorrect airflow detected, SAIS
There were a few others relating to voltages but I think that was due to removing/replacing battery, and those codes no longer appear.

After replacing the O2 sensor, the same codes are appearing, except the internal resistance too high code.
Whats the use of me putting up the complete scan when I can just tell you what codes came up? I would put it up-just not available right now.
Can anyone tell me if my MAF numbers seem correct from previous post and what typical boost pressures should be seen on a stock 225 with APR 93 flash (requested and actual)?
Has anyone have any info on the fuel delivery, I guess it could be from clogged injectors, fuel pressure regulator, fuel pump, (just replaced fuel filter), any thoughts on this?


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (maccos)*

Here is my Scan from Tuesday, Dec. 15th:
Tuesday,15,December,2009,16:31:02:59917
VCDS Version: Release 908.1
Data version: 20091018
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

Chassis Type: 8N - Audi TT
Scan: 01 02 03 08 15 17 22 35 37 45 55 56 76 77

-------------------------------------------------------------------------------
Address 01: Engine Labels: 06A-906-032-AMU.lbl
Part No: 8N0 906 018 AT
Component: 1.8L R4/5VT G01 0003 
Coding: 06710
Shop #: WSC 02320 
1 Fault Found:
17536 - Fuel Trim; Bank 1 (Mult): System too Lean 
P1128 - 35-10 - - - Intermittent
Readiness: 0000 1000
-------------------------------------------------------------------------------
Address 03: ABS Brakes Labels: 8N0-907-379-MK20-E.lbl
Part No: 8N0 907 379 E
Component: ESP 20 CAN V004 
Coding: 18446
Shop #: WSC 01236 
No fault code found.
-------------------------------------------------------------------------------
Address 08: Auto HVAC Labels: None
Part No: 8N0 820 043 A
Component: TT-KLIMAVOLLAUTOMAT D03 
Coding: 00140
Shop #: WSC 01236 
1 Fault Found:
00604 - Potentiometer Positioning Motor for Air Flow Flap (G113) 
30-10 - Open or Short to Plus - Intermittent
-------------------------------------------------------------------------------
Address 15: Airbags Labels: None
Part No: 8N8 909 601 
Component: Airbag Front+Seite 1005 
Coding: 10102
Shop #: WSC 01236 
No fault code found.
-------------------------------------------------------------------------------
Address 17: Instruments Labels: 8Nx-920-xxx-17.lbl
Part No: 8N1 920 930 E
Component: KOMBI+WEGFAHRS. M73 D08 
Coding: 07244
Shop #: WSC 40824 
No Faults Found
or DTCs not supported by controller
or a communication error occurred
-------------------------------------------------------------------------------
Address 22: AWD Labels: 02D-900-554.lbl
Part No: 02D 900 554 B
Component: HALDEX LSC ECC 0006 
2 Faults Found:
00526 - Brake Light Switch-F 
27-10 - Implausible Signal - Intermittent
01155 - Clutch 
04-10 - Mechanical Malfunction - Intermittent
-------------------------------------------------------------------------------
Address 35: Centr. Locks Labels: 8Nx-962-267.lbl
Part No: 8N8 962 267 A
Component: Central Lock/Alarm D04 
Coding: 15884
Shop #: WSC 01236 
No fault code found.
-------------------------------------------------------------------------------
Address 37: Navigation Labels: Redir Fail!
Part No: 4B0 919 887 B
Component: Navigation BNO 0001 
No fault code found.
-------------------------------------------------------------------------------
Address 45: Inter. Monitor Labels: 8E0-951-177.lbl
Part No: 8N8 951 177 
Component: Innenraumueberw. D09 
Coding: 00001
Shop #: WSC 00000 
No fault code found.
-------------------------------------------------------------------------------
Address 55: Xenon Range Labels: 4B0-907-357-AUT.lbl
Part No: 4B0 907 357 
Component: LEUCHTWEITEREGLER D004 
Coding: 00010
Shop #: WSC 01236 
No fault code found.
-------------------------------------------------------------------------------
Address 56: Radio Labels: None
Part No: 8N0 035 186 A
Component: Radio D05 
Coding: 00517
Shop #: WSC 01236 
No fault code found.
End ---------------------------------------------------------------------


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## Dana @ Ross-Tech (Sep 15, 2009)

*Re: O2 Sensor Voltage (maccos)*

Thank you for the scan. This shows us the needed details including the actual faults, installed control modules, software levels, coding, etc..
If you are reading the mentioned value of 15% then 22% from Measured block 32, there is something very wrong with this. This is the reason for that fault. Please give us the data from both fields 1 and 2 to confirm.
Please see:
http://wiki.ross-tech.com/inde...04392
If you do not have any vacuum leaks present and the Front O2s is doing its job, then the most likely faulty component is the Maf.


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## vwemporium (May 27, 2002)

*Re: O2 Sensor Voltage (Dana @ Ross-Tech)*

Yeah or just put an air mass in it or fix the vacuum leak.
Is it density of air or your head?
I logged the data but have absolutely no idea what Im doing.
Genius, super genius.
http://www.youtube.com/watch?v=STeVTzWelns
Read up on readiness procedures.


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (vwemporium)*

Im going to check and see again if there are any vac leaks this weekend, went into limp mode this morning while on cruise control, I have a feeling unmetered air is getting in somewhere or fuel injectors are not keeping up. Im pretty sure the MAF is good based on my logs and my O2 sensor is brand new soooo that "should" be good too. 
I hope I find a big ol leak somewhere, any one know off hand if your on cruising control at 70mph around 3000 rpm is the intake in a vacuum state or above the barametric pressure (boosting), lets say when your going a little downhill, so the engine isnt working real hard.
Reason I ask is if there is vacuum at these RPMs it will be sucking in unmetered air, causing lean condition and going into limp mode while on cruise control, but if there is boost always then I would be losing air and not gaining air resulting in a rich condition, ya know??
I guess I could just confirm this with my VAG COM...


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## vwemporium (May 27, 2002)

*Re: O2 Sensor Voltage (maccos)*

Bad hypothesis Super Genius.
A vac leak is, usually constant, not Sporadic.
You don't even know how to log you haven't done your readiness tests yet.
You cant log until learned values are stored or your just walking in circles.
Unless you know what values are at base line and you haven't even done a default.
Do this first.
01-02-05 erase
01-10-00 save clear defaults
01-07-same data
Re ADP 01-04-060
Then readiness tests, then log the maf.








I sound stupid because I am.
Best,
Jack


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (vwemporium)*

Where did I miss this info about a readiness test before begining logging? So exactly what does readiness do? Make the sensors ready by kicking them in the butt and waking them up?
Is the car supposed to be running during the readyiness tests?
Where can I read about the correct logging procedures?
JACK??


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (maccos)*

Just did what Jack mentioned, not sure what I was doing or why yet...
Then ran the car a little,
peak boost requested = 19 psi
Max Pressure at manifolt = 17 psi
Max Air Flow = 175 g/s
Idle trim = 0
Part throttle trim was zero upon reset and now at 7% after 10 min drive, probably will continue to go up.
Makes sense the a leak wouldnt be sporadic, but MAF numbers seem good, why would I replace it, defeats the purpose of having VAG COM?
HMMmm


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## vwemporium (May 27, 2002)

*Re: O2 Sensor Voltage (maccos)*

The repair manual.
This forum doing a search.
Its the learned adaptation values that Im referring to.
Once you go past the ability of the ecu to compensate through ADP values ( learned and table threshold ) You get DTC's.
With a device like an air mass it can lie to you and the diagnostics in the car even. To the point sometimes where you wont get a DTC and still have an issue with performance.
Here this is not the case, you have a DTC.
Its always changing but if its wrong you get the result you have.
The scan tools are guides, not a substitution for knowledge of the way the system works.
Read the Bosch self study books from RB publishers on ME ECU's.
Hope that helps.
Best,
Jack


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## maccos (Oct 18, 2009)

*Re: O2 Sensor Voltage (vwemporium)*

Hmmm, welp no leaks to be found tonight, definatly no leaks in the intercooling hoses, turbo seems to be leaking oil into intake...bummer, there are about 5 lines coming off the intake mani and upon visual inspection they all look good, didnt bother taking manifold off, looks like Im going to have to break down and buy a MAF, fingers crossed. 
Thanks everyone for your help, I still have to figure out how to exactly use this VCDS, the only thing I know how to apapt is idle...woot woot!


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## vwemporium (May 27, 2002)

*Re: O2 Sensor Voltage (maccos)*

Cool 
I hope it fixes the issue for you.
Best,
Jack


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## Borfasul3 (Aug 29, 2016)

Guys need help please...my new 02 pre-cat sensor aging in 0.54,and my second field in block 033 is fluctuating between 0.2 and max 0.89 V, i saw that must be 1.48-1.56V am I right?


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