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O2 Sensor Problem

sensor o2 fault

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#1 Sutol

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Posted 01 July 2019 - 08:33 AM

I have a S/C stage 2 running OBD Tuner. Car has run fine since 2014. Last year I got an EML. Torque revealed a problem with the O2 sensor. Cancelled the code and after a short while the EML came back on. Left it like that (but didn't drive it) until I took it into BoT for it's yearly check over in April this year. They changed the sensor.

 

Since the change this is happening. From cold, get the car up to temp and the EML will come on. Cancel EML once warm and it will stay off. Allow the car to cool and then run up to temp and EML will come on. BoT thought faulty sensor so changed it but same thing happens. These are Bosch sensors not cheapies.

 

It will be going back to BoT later this month, is there anything they should be checking for?

 

Link to Torque Fault Log https://photos.app.g...SJRwQVgt5Cu3sL8

 

Cheers Chris

 

 



#2 smiley

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Posted 01 July 2019 - 09:08 AM

Do you still have a cat?

 



#3 172Cup

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Posted 01 July 2019 - 09:16 AM

Cracked manifold?



#4 Sutol

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Posted 01 July 2019 - 09:39 AM

Do you still have a cat?

Yes 100 cell and its a Tullet 3" system to a tullet 2.5" manifold if that could be relevant

 

Cracked manifold?

Thanks I'll get BoT to check. As above its the 4/1 tullet 2.5" manifold.

 

I initially though it was temperature related ie a wire expanding and going open circuit but once the fault is cleared the EML stays off until it left to go cold.



#5 smiley

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Posted 01 July 2019 - 10:18 AM

 

Do you still have a cat?

Yes 100 cell

 

 

I got a 0140 and later a 0141 when my cat section was damaged last year.

Switched sensors, made no difference (obviously :happy:)
0141 has also been reported on a broken tmap.


Edited by smiley, 01 July 2019 - 10:18 AM.


#6 Arno

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Posted 01 July 2019 - 10:46 AM

I initially though it was temperature related ie a wire expanding and going open circuit but once the fault is cleared the EML stays off until it left to go cold.


Lambda heater circuit/connection likely bad. P0141 in that case. Heater circuit in the censor gets used most of the time to get the sensor up to temperature when cold, so the ECU notices it's faulty. P0137 pops up when the sensor is cold as it won't work yet until it reaches a high enough temperature.

Once the car/exhaust is up to temp is usually doesn't need much help keeping the right temperature so the ECU won't notice a heater fault until it has cooled down again.

As the sensor was replaced (I hope they swapped the correct one ;) ) that's likely OK now but the problem could well be (and originally also be) in the wiring loom from the ECU to the lambda sensor connector having a bad/intermittent connection.

 

Bye, Arno.



#7 Sutol

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Posted 01 July 2019 - 01:56 PM

The wiring loom north of the connection to the O2 sensor will need to checked for sure.

 

C



#8 vocky

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Posted 01 July 2019 - 04:24 PM

some early cars (pre 2002) have the post cat lambda wiring going through the loom of doom plugs, so might be worth checking those too.



#9 Sutol

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Posted 01 July 2019 - 06:32 PM

The LoD plugs are the ones under the header tank yes?

#10 markanswrth

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Posted 02 July 2019 - 01:40 PM

Interesting to hear what you find out with this as I started getting exactly the same issue a few month's back. I also have a 100cell cat and 3inch system.

 

I am going to get rid of the loom of deeom connectors all together soon as the car also occasionally goes into limp mode that I'm pretty certain is a LOD issue so will be interested to see if this sorted the P0141 issues too.



#11 vocky

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Posted 02 July 2019 - 04:29 PM

The LoD plugs are the ones under the header tank yes?

 

that is correct

 

 

X2  - blue plug
pin 1 = bn/pk (pin 87 of relay K18, +12v for fuel injectors)
pin 2 = wh/bk (instrument - rev counter) + (start relay K24 pin 9)
*   pin 3 = brn/red (post cat lambda) *
*   pin 4 = blk/red (post cat lambda) *
pin 5 = gn (+12v FuseBox 7, switched)
*   pin 6 = blk/red  (post cat lambda) *
*   pin 7 = brn/pink (post cat lambda) *

pin 8 = wh/vt (+12v for relay coil, pin 85 - fuel pump relay K16)
pin 9 = gn/bu (instrument - coolant temp gauge [pwm-pulsed signal from ecu])
pin 10 = n/c
pin 11 = n/c
pin 12 = gn/pk (0v for relay coil, pin 85 - ECU relay K18)
pin 13 = bu/gy (0v for relay coil, pin 85 - radiator fan relay)


X3 - black plug
pin 1 = ye (throttle pedal)
pin 2 = gn (throttle pedal)
pin 3 = bu (throttle pedal)
pin 4 = bk (throttle pedal)
pin 5 = wh (throttle pedal)
pin 6 = bn (throttle pedal)
pin 7 = n/c
pin 8 = bn/bu (instrument - oil pressure light)
pin 9 = wh/ye (immobiliser)
pin 10 = bn/bu (instrument - engine management light)
pin 11 = ye/gy (ABS pin 3 - speed signal for engine ecu)
pin 12 = n/c
pin 13 = vt [+12v FuseBox 8, permanent]



#12 Sutol

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Posted 07 July 2019 - 08:55 AM

OK, I've done some further investigations. I have used OBD Tuner to log what the 2 O2 sensors are sending to the ECU.

 

This log is a trace of when the car was running normally.

 

https://photos.app.g...5H6WxsJMwCm4Ga6

 

This log is a trace is showing what I'm getting at the moment.

 

https://photos.app.g...5CgnVKNgrfJgWk7

 

So the ECU is not getting a signal from the secondary O2 sensor, should be getting something like the primary. The EML came on about 2/3rds of the way through that trace. Now what I can't quite understand is why I'm not getting an EML as soon as I start the engine. Any ideas??

 

The next thing is to check for continuity in the wiring and also check the plug connections as Vocky suggested. The LoD plugs were given a good spray with contact cleaner but now they need to be carefully checked.

 

Any further suggestions gratefully received as always.

 

Cheers Chris



#13 techieboy

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Posted 07 July 2019 - 10:35 AM

Not sure a fault on the secondary sensor is critical enough to the running of the engine to give an instant EML and it may just be treated as a pending fault.

The secondary O2 sensor on my Audi has been fcuked for a couple of years but only trips an ECU fault once or twice every 3 or 4 months before giving up telling me and resetting the EML.

#14 Sutol

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Posted 07 July 2019 - 10:47 AM

Not sure a fault on the secondary sensor is critical enough to the running of the engine to give an instant EML and it may just be treated as a pending fault.

The secondary O2 sensor on my Audi has been fcuked for a couple of years but only trips an ECU fault once or twice every 3 or 4 months before giving up telling me and resetting the EML.

Everything i've read says it's not critical but once the eml is on it masks potentially more critical problems which may occur. For this reason I cancel the error code but it happens a lot more than you're experiencing Matt. You might find that, as yours has been laid up for a while, your car will start doing it because mine has started doing it after a near 5 month lay off (not 5 years!!).



#15 techieboy

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Posted 07 July 2019 - 12:59 PM

It may well do, if it ever gets started again.

It already chews up wide ands every few hundred miles anyway. Though at least that doesn't trip a fault code on the dashboard.

#16 El Duderino

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Posted 07 July 2019 - 03:08 PM

Maybe the second O2 Sensor was connected to the wrong plug, since there are two in that area of the engine bay that both fit, but only one is used by the Ecu. I connected it wrong myself once, after changing the Sensor. The other plug may only be used in other gm vehicles, i don't know.

#17 Sutol

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Posted 07 July 2019 - 09:51 PM

I'm sure it's been plugged in correctly but I'll check.

Peter (OBD Tuner) has informed me that the sensor has to record a fault several times before an EML is activated, so that answers that one.

#18 chris_uk

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Posted 07 July 2019 - 10:04 PM

I can send you an NGK one if needed..

#19 Sutol

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Posted 08 July 2019 - 06:27 AM

If you could Chris I'd be obliged. Be good to check with one that is known to work.

#20 Sutol

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Posted 15 July 2019 - 01:13 PM

Just spent the morning at BoT and a pinched wire that had shorted against the sub frame was found. This resulted in the insulation on most of the wire melting. All the damaged wiring was replaced. Trouble is the fault is still there. The cable that was damaged was the pink/brown one pin 7. The voltage readings at the plug are different to the ones on the primary sensor, should they be the same (engine off/ignition on)? Any other suggestions gratefully received as always. C

Edited by Sutol, 15 July 2019 - 01:14 PM.






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