02 Sensor Heater resistance tolerance

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02 Sensor Heater resistance tolerance

Postby Avdr » Sun Dec 23, 2012 7:18 pm

Hi all,

For a while now I've been trying to defeat the issues of running a decatted car - when it comes to lambda sensor errors in particular.
First stage is to defeat the heater circuit, I had this sussed once, using a home made coil of heater element wire, at 10ohm. 10ohm was the resistance I measured from a sensor on the car that at the time was not causing any errors.

Having proved the success of the heater element wire, I decided to neaten the job up using proper wire wound resistors, obtained 2 x 10 ohm power resistors at 25W - one resistor for each bank, and therefore 1 per (removed) sensor. This was never as succesful though, and often would report heater errors.
I have had a little time recently and set about trying to get to the bottom of this. Measuring cold resistance of 2 other sensors I obtained 8.6 and 8.4 ohm, so began a search for a data sheet for LSF4 sensor by bosch. Eventually I found the info I wanted, which is that a brand new sensor should have heater resistance of 9 ohm.

Problem is nobody really makes a 9 ohm power resistor, and I havn't had much success trying to find two values that would total 9 ohm and could be used in series with one another.

So... Does anybody have experience of the tolerances within which an ECU will accept a heater circuit, and by extension at what point is it considered fautly? ECU in question is a Bosch ME 3.1.1

Armed with that tolerance I could pick a resistance value that would fall within spec.


Thanks
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Re: 02 Sensor Heater resistance tolerance

Postby GRUSS » Mon Dec 24, 2012 11:21 am

Hello there

What car have you got and what's the reason behind loosing the cat? When I had my track car a few years back I just used a O2 simulator.... Did the job
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Re: 02 Sensor Heater resistance tolerance

Postby Avdr » Mon Dec 24, 2012 2:42 pm

Hi,
Its a v6 vectra B 2.6. Engine code Y26SE
It has manicats as standard on both banks then a 3 way in exhaust system after flexi. Decided to ditch the mani's as the cats themselves were scrap anyway when I bought the car, along with some other fettling I've managed to drag an extra 40bhp out of it on standard management.

Getting fed up of the EML glaring at me though, its either leave the sensors in and get p0420 & p0430 or blank the bosses and work around - saves spending £150+ on lambda sensors I'm not even using.

I've been looking at getting it mapped but can't find many places that can map it, the one place I did find locally didn't even intend to map on the rollers :roll:
Might buy a dimsport genius and have a look at mapping it myself along with some dyno time, that way I could remove the post cat lambda's completely.
Anyone reading this with experience of dimsport genius 2, please chip in with how well it works etc.
Thanks
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Re: 02 Sensor Heater resistance tolerance

Postby KimAndersen » Wed Dec 26, 2012 10:29 am

Hi Avdr

It's not that simple - just putting a 9 ohms in the lambda circuit. To start with - the heater element in a lambda sensor does have a resistance of 9 ohm when it is cold and when the engine is warmed up - will there be a resistance change in the heater element.

The resistance in the heater element can reach as high as 30Mohm and according to Bosch the signal is fully decoupled.

The ceramic heating element has a PTC characteristic.

According Ford - is the tolerance on a bosch lambda heating element this

Heater current outside limits: < 0.400 amps or > 3 amps, (Bosch)



Kim
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Re: 02 Sensor Heater resistance tolerance

Postby Avdr » Wed Dec 26, 2012 4:12 pm

Hi Kim, thanks for the reply. I realise that the resistance will change with temperature, but feel that I proved initially with my heater element experiment that the ECU can be satisified the heater circuit is ok, even if the circuit isn't exposed to temp variations as seen in an exhaust.

Furthermore, I have found that when using lambda sensors with intact heater circuits, the sensor can be left in free air and still satisfy the heater circuit check.
Ofcourse in all cases, be it the sensor itself, a length of heater element wire, or a power resistor, the component will always heat up and with this a change in resistance will occur.

I'm a little confused when you state that a heater could show resistance of 30Mohm, that would bring the current down to virtually nothing, and would fall out of range of your values stated of 0.4< Current (A) < 3.0

Thanks for the info,
Andy
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Re: 02 Sensor Heater resistance tolerance

Postby KimAndersen » Wed Dec 26, 2012 7:15 pm

Hi Avdr

I wasn't totally clear in my statement - i apologize for this.

The fact is that it is taken from two sources - one from a official document from Bosch regarding the resistance in the heating element and the other about the values of current running through the lambda sensor is taken from a document called " FORD - 2001 MY OBD System Operation "

I know - if you use OHMs law - that it don´t make any sense.

So the values - must be taken independent of each other.

Kim
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Re: 02 Sensor Heater resistance tolerance

Postby hexibot43 » Wed Dec 26, 2012 9:34 pm

Avr,

Those codes you are getting are not for the heater circuit. They are for Catalytic Efficiency which is calculated by looking at the relationship between before and after cat oxygen sensors signals. Something like a P0135 would be a problem with the heater circuit. So changing the resistance of the heater circuit isn't going to stop those codes. The o2 simulator would work as mentioned, but If I were you I'd be going the way of software like you were talking about. I have not personally done anything with the pcm on that particular car. But I have chipped plenty of cars. You should be able to disable the code reporting function for the codes you are having trouble. There are some cars that use the after cat o2s to help with fuel trim. Something to think about. They are not all used simply for CAT monitoring.
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Re: 02 Sensor Heater resistance tolerance

Postby Avdr » Wed Dec 26, 2012 10:47 pm

Hexibot, thanks for the reply.
I think you've misread the posts so far, P0420 & P0430 are the codes I would get if I fitted two new lambda's into the post cat bosses. When I first bought the car, this was the case anyway as both CATs were beyond service.
Having now removed the CATs the situation would be the same - fact is I don't want the expense of two sensors needlessly sitting in the system - would prefer to defeat them. Plus its all interesting stuff - learning by trial and improvement what can and cannot be achieved.

RE: the fuel trims, the LTFTs both look good, I've no cause for concern there. STFTs also react well to deliberate loads, heated screen, aircon compressor etc.
I've done pretty extensive testing with wideband lambda sensor kit, and the system is still coping just as it did before the modifications.

I would love to map it as its running extremely rich at WOT (always has). Just such a difficult ECU to map for a reasonable cost outlay. Its a 12 year old car and not worth spending big money on.

Andy
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Re: 02 Sensor Heater resistance tolerance

Postby hexibot43 » Thu Dec 27, 2012 5:12 am

I just read it again. I must be getting old....it still looks to me like you are worried about the resistance of the o2 sensor heater circuits. And all I was trying to say is that would not give you those codes. It would give you p0135 for open circuit with a missing heater. What you would need to worry about is the waveform generated by the signal wire of the o2 sensor to make the computer happy. The 10 ohm resistor would easily take care of the heater part of the circuit. It's the other half you are missing from what I see.

Can you get a dump of the ecu? What year is the vehicle I have a lot of info on the bosch ecus. But I'd need you to send me a dump of the rom.

I just did some looking around....we didn't have that particular ecu on this side of the pond. But if I could see the code I might be able to do something with it.

Mab
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Re: 02 Sensor Heater resistance tolerance

Postby KimAndersen » Thu Dec 27, 2012 11:37 am

I would like to make a correction of my earlier posts regarding the Bosch heating element resistance of 30 Mohm.

I have misinterpreted this info from Bosch - it is not correct, that there is 30Mohm in heating element of a Bosch Lambda Sensor, when it is fully warmed up.

It is however still true - that the resistance changes when it is warmed up by the exhaust gas - but not to 30 Mohm !

Here is what there stood in the document - a direct copy and paste from this Bosch document.

Heated Lambda sensor LSH

Design

Basically, the heated Lambda sensor is identical to the unheated version.The active sensor ceramic is heated from the inside by a ceramic heating element so that it remains above the 350°C function limit independent of the exhaust-gas temperature. The ceramic heating element has a PTC characteristic so that it heats up quickly and needs only very little power when the exhaust gas has heated up. The heating-element connections are fully decoupled from the sensor signal line (R>30Mohm)

I apologize if i have caused some confusion regarding this subject.

Kim
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