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Jeremy Cottrell

O2 sensor resistance readings

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The car is a 2001 Boxster non-S with a code P1126.

RKAT readings for bank 1 are 0

RKAT readings for bank 2 are 0.58

MAF is around 13 - 14

Looks like we have bank 2 running a little lean. Checked for vac. leaks, nothing found. Checked AOS, no leaks, oil cap easy to remove.

O2 sensor voltage all ranging .27 - .89 V

O2 sensor resistance:

Bank 1 - ahead of cat = 384 ohms

Bank 1 - behind cat = 64 ohms

Bank 2 - ahead of cat = 64 ohms

Bank 2 - behnd cat = 128 ohms

I cannot find any data for the resistance numbers.

Any idea if these numbers are just as a result of the lean mixture or a problem with an O2 sensor itself, or ??

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RKAT values are in % so 0% and 0.58% are very small numbers and are normal. What are your FRA values on both banks?

Checked oil filler tube for leaks? Usually O2 sensors have their own codes. Were the readings taken at engine at idle (looks like so based on the MAF reading) after fully warmed up and a/c off?

Edited by Ahsai

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The car is a 2001 Boxster non-S with a code P1126.

RKAT readings for bank 1 are 0

RKAT readings for bank 2 are 0.58

MAF is around 13 - 14

Looks like we have bank 2 running a little lean. Checked for vac. leaks, nothing found. Checked AOS, no leaks, oil cap easy to remove.

O2 sensor voltage all ranging .27 - .89 V

O2 sensor resistance:

Bank 1 - ahead of cat = 384 ohms

Bank 1 - behind cat = 64 ohms

Bank 2 - ahead of cat = 64 ohms

Bank 2 - behnd cat = 128 ohms

I cannot find any data for the resistance numbers.

Any idea if these numbers are just as a result of the lean mixture or a problem with an O2 sensor itself, or ??

RKAT values are in % so 0% and 0.58% are very small numbers and are normal. What are your FRA values on both banks?

Checked oil filler tube for leaks? Usually O2 sensors have their own codes. Were the readings taken at engine at idle (looks like so based on the MAF reading) after fully warmed up and a/c off?

Ahsai is correct about reading your FRA (load) and TRA (idle) adaptation values for the bank. Far too often, we see people reading what they perceive as O2 sensor codes that are actually not the sensors, they are the sensor's response to another problem; yours is exactly that. P1126 indicates your bank is reading lean, not because of the sensors on that bank, but because of what they are seeing: not enough fuel. If the sensor had a voltage, resistance or communications issue, you would get specific codes for that. This P1126 code typically comes from either low fuel delivery (pump pressure or delivery rate, or a plugged injector), or an air leak in the system. Check your fuel system pressure and delivery rates, if they are OK, pull the plugs on that bank and look at their color; a lean cylinder from a bad injector will be white while the others are brownish and sooty. If the plugs are OK or even in color, you have a vacuum leak somewhere in the system, and this is where it typically gets very messy as the leaks are often very small, or internal to the system (jammed or bypassed valve on the EVAP control system). These leaks just don't jump out at you, you need to systematically search for them, particularly looking at any vacuum connections that feed into the intake for that bank.

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FRA is 1.00 on both banks.

That's interesting you mentioned EVAP control system. This car has trouble at the gas pump. It only takes a couple gallons at a time.

That is weird as the FRA range limits on adaptation for both banks are Rich: 1.25 and Lean: 0.75; so the car seems "inbounds" when the car is under load. What are the TRA (idle) values, and have you tried clearing the code and then seeing if and when it returns? I'm wondering if you have an intermittent issue here.............

Fuel filling problems were common on the earlier 986/996 cars, do a search and you will find several recommendations on how others have addressed there issues.

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Yea, 1.00 FRA is definitely strange for P1126 like JFP explained. Any freeze frame data you can retrieve before you reset it? That may give us more clue under what condition the code was tripped.

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I went down the road in the car. FRA was 1.00 to 1.04. At idle 1.00 steady for both banks. RKAT for bank 2 got up to 0.75%, bank 1 stayed at -0.05%

All well within specs. Have you tried clearing the code like JFP suggested?

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Yes. 1126 comes back. It takes awhile but it comes back. It may be one of those situations where whatever the problem is it will need to get a little worse to actually find it.

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I have this very same issue now.  (2000 Boxtser S)

 

Since this was over 4 years ago, did you ever come to a conclusion as to what the issue was Jeremy?  Mine code is intermittent.  The car has a bit of a rough idle at initial startup in the morning, and I can go a couple hundred miles before the 1126 even comes back.  Otherwise, the car runs fine.

 

It seems to throw the code when I am cruising on the freeway, under light load, maybe 2500 rpm in 6th gear, maybe 75-80 mph, and then boom, CEL.

 

Any idears?

 

Thx,  Brian

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