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      01-07-2014, 01:32 PM   #1
Beedub
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Pre cat and post cat 02 sensors.

Ok so one of my POST cat O2 sensors has gone AGAIN, now I was kinda thinking about getting a specific tune to "delete" the rear post cat sensors , i have Been led to believe they aren't actually doing much apart from check emissions and cat performance. I have code p0141 which is heater circuit not getting upto temp fast enough.... I've cleared the code and it's not coming back at the moment....

Are the secondary sensors something we really need ? Would love some more info on what they are actually doing ?? AFRs and performance is identical.

I'm guessing pre cat sensors are the ones providing fuel trims etc ....
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      01-08-2014, 12:18 AM   #2
JeffchaPz
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Hey bud, even if you get a tune you still need to have working post O2 sensors.

I actually cut mine trying to extend when I installed my headers and the SES light was on all the time. I order a tune thinking that would turn the light off, but I was told I still needed healthy working sensors. You CAN ask them to turn them off completely but you won't inspection.


Good luck.
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      01-08-2014, 03:05 PM   #3
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afaik the post cat lambda sensors are only used to monitor the exhaust emissions in order to determine if the cat's are working fine. No active feedback to the engine management to control the engine is made.

I always thought that most tuners disabeled the check engine light coming from post cat lambda's (to get that problem out of the way ), but I guess ESS doesn't.

You're not spraying/painting the sensors with cleaning stuff or paint or stonechip or something else (oil, silicone)? (that would be bad, there are sometimes holes in the housing that give acces to reference air to compair to the air in the exhaust).
Also check if it isn't something in the wiring, if any of the cables is rubbing against something (I guess the lambda leads run behind the heat shield?)
And you haven't done some mod like the air pump delete?

If this is a recurring problem I'd go the way of using a lambda sensor simulator. (buying new lambda sensors all the time gets expensive )
Something like this:
http://www.o2simulator.com/index.php...ndex&cPath=1_9
along with the heater resistor.
I don't know if thats MOT legal, but I think the MOT only checks the emission itself.

But first of all I'd give Hans Kirkerod a call or mail Asbjorn, to see if they are familiar with this problem and how they see the use of a O2 simulator on the 2nd lambda's.
That O2 simulator is basically a timer IC with some resistors and capacitors to set a pulse value to fool the ecu. (there are probably other suppliers too).

But something is not right as lambda sensors should easily last 50k miles imho, even in a tuned engine, although the heater circuit is the most sensitive/likely to fail.
You could test the lambda sensors themselves (and the heater system) to see if the sensors themselves are at fault, or that the ecu is not giving them the right signals/voltage. When measuring the heater leads on the unplugged sensor, a working heater has a low resistance (sub 50 ohm) and a broken heater has infinite or very high resistance. I don't know what the leads of the heater in the lambda sensor connector are tbh. (I'm guessing the two white leads; the heater has no polarity, so most of the time there are 2 wires with the same color (both heater and 2 with different color (ground+signal sensor), and on my car there are 2 white leads, a grey and a black one). If you measure a low resistance on the heaterleads, then it's maybe not the sensor (checking if the sensor itself is working 100% is more difficult), but the ecu or the wiring in the rest of the loom. The power for the heater (that comes from the ecu side) is probably a pulsed 12v signal.

And always install the lambda sensors with a little bit of anti seize on the threads (but not on the sensor itself)

You could also post this question on e46fanatics, lots of engine guru's there on the s54.
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Last edited by GuidoK; 01-08-2014 at 04:02 PM.
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      01-08-2014, 04:26 PM   #4
Beedub
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Quote:
Originally Posted by GuidoK View Post
afaik the post cat lambda sensors are only used to monitor the exhaust emissions in order to determine if the cat's are working fine. No active feedback to the engine management to control the engine is made.

I always thought that most tuners disabeled the check engine light coming from post cat lambda's (to get that problem out of the way ), but I guess ESS doesn't.

You're not spraying/painting the sensors with cleaning stuff or paint or stonechip or something else (oil, silicone)? (that would be bad, there are sometimes holes in the housing that give acces to reference air to compair to the air in the exhaust).
Also check if it isn't something in the wiring, if any of the cables is rubbing against something (I guess the lambda leads run behind the heat shield?)
And you haven't done some mod like the air pump delete?

If this is a recurring problem I'd go the way of using a lambda sensor simulator. (buying new lambda sensors all the time gets expensive )
Something like this:
http://www.o2simulator.com/index.php...ndex&cPath=1_9
along with the heater resistor.
I don't know if thats MOT legal, but I think the MOT only checks the emission itself.

But first of all I'd give Hans Kirkerod a call or mail Asbjorn, to see if they are familiar with this problem and how they see the use of a O2 simulator on the 2nd lambda's.
That O2 simulator is basically a timer IC with some resistors and capacitors to set a pulse value to fool the ecu. (there are probably other suppliers too).

But something is not right as lambda sensors should easily last 50k miles imho, even in a tuned engine, although the heater circuit is the most sensitive/likely to fail.
You could test the lambda sensors themselves (and the heater system) to see if the sensors themselves are at fault, or that the ecu is not giving them the right signals/voltage. When measuring the heater leads on the unplugged sensor, a working heater has a low resistance (sub 50 ohm) and a broken heater has infinite or very high resistance. I don't know what the leads of the heater in the lambda sensor connector are tbh. (I'm guessing the two white leads; the heater has no polarity, so most of the time there are 2 wires with the same color (both heater and 2 with different color (ground+signal sensor), and on my car there are 2 white leads, a grey and a black one). If you measure a low resistance on the heaterleads, then it's maybe not the sensor (checking if the sensor itself is working 100% is more difficult), but the ecu or the wiring in the rest of the loom. The power for the heater (that comes from the ecu side) is probably a pulsed 12v signal.

And always install the lambda sensors with a little bit of anti seize on the threads (but not on the sensor itself)

You could also post this question on e46fanatics, lots of engine guru's there on the s54.
thanks guido, youve pretty much nailed it, i was certain the post cats were not feeding back to make fuel trim calcs etc.... thanks for throwing in your knowledge here.....

ill wipe the code and see if it comes back, if it does then ill make some moves on this.....
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