02 legacy misfire and 02 codes

Which is why I'm not yet throwing parts at it because I'm not 100% sure. I'm going off a combo of gut feel, experience, and my Firebird shop manual for troubleshooting P0130 and related codes. One of the things in there for checking lean conditions is to check for intake leaks and/or exhaust leaks upstream of the 02 sensor(s). However, even then, you'd think that the value for the 02 sensor should be changing as the computer is trying to richen it up, which is NOT happening, which causes the second code for "too lean" (P 0171 IIRC) And because it's not "major serious" like no oil pressure or a busted rad hose, I'm not in any huge rush to throw parts at it on the possibility it might fix it. They already changed the plugs and wires on it...

and does anyone know how to clean an 02 sensor? Carb cleaner? Brakekleen? Sandpaper?

Ray (and I ordered a shop manual CD off ebay, so I should be in a much better position to diagnose and repair this thing shortly.)

=================================================================== the sensor may be carbon fouled. It is sometimes possible to clean a sensor in the car. Do this by unplugging the sensor harness, warming up the engine, and creating a lean condition at about 2000 rpm for 1 or 2 minutes. Create a big enough vacuum leak so that the engine begins to slow down. The extra heat will clean it off if possible. If not, it was dead anyway, no loss. In either case, fix the cause of the rich mixture and retest. If you don't, the new sensor will fail.

Lg

READ THIS FIRST:

Lg

Of course...

Not changing is odd... Would expect to see some kind of response.

Is the post cataylst O2 sensor the same? If so you could swap them. If the malfuction moves to sensor 2 or starts giving a code for a cataylst malfunction then you'll know it's the sensor.

thanks. :)

And next question... what's the difference between a pre-cat and post-cat 02 sensor? Less worried about construction, more a question of what "normal" output would look like for both.

Should they both hover around the 450mV mark under idle/normal load? Will the pre-cat one move around more as the throttle is opened/closed while the post cat one should remain fluctuating back and forth? From what I've read it's not always possible to read this without a scope as it switches back and forth too fast for a meter or even my autotap to display correctly.

Ray

The toggle rate of the switching between low voltage 0 point something and a high of nearly 1 volt.

My scanner shows the voltage values. I don't know what a scope image would look like other than a flat bar indicating a low voltage to high voltage and then back to low...Direct Current

That's the *toggle threshold* where anything below is considered low, anything above is considered high.

IIRC, pre-cat toggles at about 2 cycles/second post cat toggles at 127th that rate, as a general example.

read it without a scope? My Actron 9145 catches it every time. Even my Davis Drive Rite chip catches it, with a sampling rate of once every 5 seconds.

2 hertz, 2 cycles/second, should show up fine on any analog voltmeter, even a $3 volt meter from Harbor Freight, but you have to backprobe the *output* wire to the ECM, and put the ground wire from the volt meter on the engine block which is B-.

Me, I use the scanner and the Chip at the OBDII port under my dashboard. It is easier for me, believe it.

Lg

I don't think this engine has a "hot wire" type sensor. It has a MAP.

Ray: Provide me with your email address and I will forward you the diagnosis procedures from the manual for my 03 outback, they should be pretty much the same. snipped-for-privacy@juno.com. Please put SUBARU in the subject line so I do not toss the email as spam.

Good luck

AS

Ray wrote:

Brent:

They are 2 different kind of sensors, they cannot be swapped and doing so could lead to ECM damage.

The b1s1 sensor is a wide range sensor, it can continuosly change the current output to the ECM. It is called and air/fuel A/F sensor.

The b1s2 sensor is a narrow range sensor and it is almost > >

Had a bad feeling suburu might do it that way. And of course swaping without checking first would be foolish.

That is what I thought it might be in this case, but it's worth getting the question answered. The swap option in diagnosis is closed off unfortantly.

That said, from a manufacturing/design perspective the goal would be to make those sensors the same part even if if one would not be used to it's potentional. There would need to be good reason not to, such as the front sensor needed to be considerably better because of how the ECM works and there was a large cost difference. The wide band sensor is proabably still too costly to be used in both locations.

Some vehicles only use a single sensor type for both locations because it's all that's needed and doing so saves on costs from volume, inventory, etc.

At (IIRC) 23% fuel correction, it may be at its limits for adding fuel. Fuel trims don't usually go much over 20%.

You can try adding propane from an unlit propane torch and then watch the O2 sensor for response.

The front sensor is exposed to a different, hotter mix of gasses. The rear one is to monitor cat efficiency. I can see their functions being different enough to warrant specific designs.

I dunno

Carl

The older 'narrow band' type certainly can survive and do the job to control mixture well enough. Wideband O2 sensors have only been around since the mid 90s or so.

Looking into this further it appears that wideband sensors have been put into use for meeting the various LEV emissions standards.

Poking around some, it's the earlier OB2 cars where having the same sensor type before and after catalyst appears more likely.

Neil, This Subaru has an air/fuel ratio sensor for B1S1. The research I've done has spotty results so I was reluctant to post it, but it appears like the max range you would expect to see out of this sensor is from .025 volts to about 1.1 volts. It should stay near the center and not move much on a properly running car. I don't know if it responds in the reverse manner like 3v/3.3v comparator A/F sensors (scantool A/F parameter --> 5 volts is lean, 0 volts is rich), but I would suspect so as it is an ion pump style sensor. The original post mentions -23%LtFT

*and* P0171 too lean. That doesn't jibe, so perhaps the minus mark was a typo.

Toyota MDT in MO

It was a bad B1S1. And over the course of the weekend, it threw both a P0130/P0171 and a P0130/P0172 combo with a P0301/P0302/P0303/P0304 in between. When I first checked, LTFT was at "max lean" and then later at "max rich." Basically, the pre-cat 02 appears to have been "stuck" at one end of the range or the other, thus causing the computer to lean it waaay out, or richen it waaay up, and freak when it hit the limit. Anyway, they changed the 02 and it runs way better now.

So, yes, the -23% was a typo... that happened later when it threw the P0172. Ray

Been a few years since the wideband class, IIRC, the current varies with mixture, but it's a bitch to measure in the conventional manner. Scan tool re-interprets it into voltage as the PID.

I personally haven't seen any failures on that type of system, although I'm sure they're out there.

My thought was to force a known condition and look to see if there was an appropriate reaction...

Roy posted that it was indeed a +23% trim value, not a -23%, that's what made me think that the propane trick might validate the failure before he committed the bucks for the sensor.

The whole thing reminds me that I need to get one of these crittters in and do some hands on...