stuimpreza

Hi, I am hopeing someone will be able to awnser this for me.

When I reset the ECU on my my99 Impreza WRX (Import), it keeps flashing up code 32 (oxygen sensor) and then by the time i have pulled over (approx 1 min) it is flashing the all clear message.

When I check for fault codes, there is nothing stored in the ECU.

My question is:

Do I have a faulty oxygen sensor, or is this just a random code before it resets?

Stu

bombfactorymusic

Was your engine hot or cold? Try warming engine up first then reset ECU. When the engine is cold it uses the MAF etc to control Air/Fuel mix and when engine is hot it will use Lambda(02) sensor.

Splitpin

Probably, but the only way you will find out for sure is likely to be to replace it and see if the problem goes away.

No. If you're doing the "green plugs + black plugs then drive around a bit" reset procedure, then if everything is 100% you shouldn't see any error codes until you get the all clear.

Running the ECU through this sequence forces it to do an active check of all the sensor inputs. This is why you have to drive it - as without doing so it's unable to check the speed sensor.

If it's bringing up code 32 and then eventually giving an all-clear, one possible explanation is that your sensor's on the borderline between just about working and not doing so. Under those circumstances it's probably degraded enough to be costing you some closed loop fuel economy.

If you don't have access to any data monitoring kit, the quickest way to diagnose is, as above, to replace the sensor, reset the ECU again and see what happens.

Splitpin

While I don't want to sound too disparaging to someone with postcount=1, and while I do see what you're getting at, what you've written above is just plain wrong.

There is/should be no need to prewarm the engine to give the sensor a helping hand - if you need to do so then that in itself suggests the lambda sensor is on its way out.

The lambda sensor has its own heating element and provided it is working correctly, should read correctly within a minute of starting a stone cold engine.

Your comment about the MAF setting fuelling when the engine's cold and the O2 sensor doing it when it's hot is also incomplete enough to be incorrect, but that's outside the bounds of this thread.

stuimpreza

Hi,

Yes, the engine was at operating temperature when i performed the reset, as per the instructions on Scoobypedia.

stuimpreza

Hi Splitpin,

Yes i was doing the "green plugs + black plugs then drive around a bit" reset procedure.

Thanks, you have confirmed what I suspected, and the MPG has droped a bit lately.

Could a faulty oxygen sensor also cause an intermitant slight shuddering/hesitation, and a drop in performance?

I will replace the oxygen sensor next weekend,
Is there any reason not to use an aftermarket sensor from a reputable manufacturer like Bosch?

Thanks again for your help,

Stu

Splitpin

Hmmm, it could possibly cause a slight shuddering/hesitation, but shouldn't cause a drop in performance, at least assuming you mean on-boost performance. One of the reasons I said BMF's post was wrong is that above a certain performance threshold, the ECU switches into open loop mode and calculates fuelling only on the basis of engine speed and MAF input.

As such, a jiggered O2 sensor will result in too much fuel going in on low throttle cruise but will not affect what the car does when your foot is down. If the car is weirding out under boost, the airflow meter's one obvious suspect but there are plenty of others.

It's worth devoting some effort to tracking the cause down, as if it is a faulty AFM, expensive engine damage can result from continuing to drive on it. Unfortunately, when these things start to go, they do so in a manner that won't illuminate the CEL until it's too late.

There's no reason at all not to use a Bosch three wire replacement, as aside from anything else, the OE "Subaru" sensor is actually a copy of a Bosch design manufactured under license in Japan. The most important thing to get right if you get a non-OE replacement is that you get the connector crimped on properly.

Edited to add: Have just seen your other thread, and seeing as you've already done a MAF, and you say that the juddering's most prevalent on light throttle, then the O2 sensor is certainly in the frame, especially alongside the reduction in fuel economy. New sensor, reset ECU, see where you get.

stuimpreza

Hi,

The drop in performance I have noticed is actually before boost.
When I am travelling at a steady speed and then put my foot down the revs dont rise as quickly as they did untill it hits boost (approx 3200rpm) then it picks up fine, but this has a knock on affect that the car does not feel as powerfull as it should.

When I rang my local Subaru parts department today for a price of the oxygen sensor, the parts assistant said that there was also an air/fuel ratio sensor in the o/s exhaust manifold that will give the same fault code. Are these fitted to all classic year ranges?
as i dont remember seeing one when I have worked on the car previously.

Thanks

Stu

Splitpin

There's one relatively easy way you could potentially find out, prior to replacement, whether the O2 sensor is contributing to that issue in any meaningful way: Reset the ECU, immediately you get the all clear, stop the engine and disconnect the O2 sensor (watch your hands and arms as the connector's a fiddle over a hot exhaust!).

Start up and go for a quick blat. The CEL should be on but it shouldn't be in limp mode. If it suddenly feels better, then sounds like your luck is in and you can order & fit the new sensor as soon as poss. If it isn't significantly different, then chances are you're going to be looking for another cause.

No, which the parts bloke should have known.

That's because it ain't there.

stuimpreza

Hi,

I tried to carry out the procedure you have suggested, but the ECU no longer gives the all clear code, just code 32. So the sensor is obiviously getting worse.

I knew I was not going mad and there was only the one sensor

I will replace the sensor at the weekend, reset the ECU and go from there.

Just to add insult to injury, some one reversed into the n/s this morning and wrecked the front wing enough that I can not open the front door more than a few inches

Thanks for all your help, I will post how I get on at the weekend.

Stu

joz8968

iTrader: (13)

Twucking fats!

Splitpin

Tw*tter. Hopefully you have the miscreant's details.

stuimpreza

Hi,

Yes, I have their details, luckily she came and found me after doing it.

I purchased a replacement oxygen sensor yesterday (Bosch universal - LS 02), but it has a different shaped probe to the original. The original sensor has a domed end with 3 slits in it (see link below):

http://www.boschautoparts.co.uk/pcLamb3.asp?c=2&d=1

And the new one is cylindrical with a nipple on the end that is surrounded by six holes (see link below):

http://www.boschautoparts.co.uk/pcLamb1.asp?c=2&d=1

Will this be ok to use or do you think I have been supplied the wrong one?

From the reserch I have done online it appears to be the correct part number listed to replace the one for my year of Impreza, so I am thnking it is probably just an updated design. But I just wanted to double check before I fit it, incase it will cause a problem or the JDM versions are different from those listed in the uk.

Thanks

Stu

stuimpreza

Hi,
I have replaced the oxygen sensor and reset the ECU. Got the all clear code strait away - only travelled about 10 feet

Shudder/hesitation has gone and car seems to run much smoother.

Now having problems with lack of boost, but I think this may be down to the intercooler pipes, as they have been taken off several times laterly (including when I replaced the oxygen sensor) and the one between the intercooler and trottle body is swolen with a couple of small splits on one edge (but these are on the outside of the hose clip so should'nt cause an issue).

Thanks to Splitpin for all your help, it is very much appreciated.

Stu