Oxygen Sensors Failing Frequently

January 29, 2008

Have a 2002 Rav 4, 2.0 litre VVTI. One of the pre cat Oxygen sensors failed about 18 months ago Toyota part no 89465-42090 at about 50K miles. Had it replaced at great expense and it lasted barely 12 months before it went again. Engine light on permanently. Drove it like this for about 6 months but had it changed again yesterday and it blew again on the way home from the garage!

Can't afford to spend hundreds of pounds every few weeks or months on this. I gather it is the heater circuit which goes open circuit. Does anyone know what the underlying cause is for these types of frequent failures? Also is there another supplier/manufacturer of these sensors which will replace the OEM version?

Any info gratefully received.

Thanks,

Ray

January 30, 2008

Have a 2002 Rav 4, 2.0 litre VVTI. One of the pre cat Oxygen sensors failed about 18 months ago Toyota part no 89465-42090 at about 50K miles. Had it replaced at great expense and it lasted barely 12 months before it went again. Engine light on permanently. Drove it like this for about 6 months but had it changed again yesterday and it blew again on the way home from the garage!
Can't afford to spend hundreds of pounds every few weeks or months on this. I gather it is the heater circuit which goes open circuit. Does anyone know what the underlying cause is for these types of frequent failures? Also is there another supplier/manufacturer of these sensors which will replace the OEM version?
Any info gratefully received.
Thanks,
Ray

wow

something rings a bell......is it the mixture being wrong?? I can't remember.

January 30, 2008

Same for me, I can't remember either. The oxygen sensor uses a crystal to compare the exhaust contents with the oxygen on the outside of the exhaust and makes tiny adjustments to the mixture. The trouble is I don't know if it is a fault with the exhaust (mixture as bothy says) that is bgring the sensor or if it is something in the wiring or ECU that is doing it. I would have though that it should be storing codes and these should be read to see if it can point you in the right direction. There is no point the repairer just keep throwing sensors at your expense at it.

There are a couple of good electronics guys that look in who might be able to help - shcm and JHRC or you could pm them.

I can give you the fault finding process if you pm me with your email address but trust me it won't mean a thing to you unless you are a competent engine electronics man. If you can find a good person they might like it to help them sort it out.

Unless you are due for MOT don't rush into fitting another just yet and yes you can buy them from other suppliers. Do a search for oxygen or lambda sensors.

If you pm king with your chassis no he will quote you you for genuine ones at a discounted price.

Good luck mate.

January 30, 2008

Oh blimey, I'm trying to dredge up stuff from my dim and distant past - It's been over 15 years since I did any EMS specific ECU design.

I'm certain we used to monitor lambda sensor heater current, but can't remember whether the heater was PWM (sorry probably to techy), or just a straight power transistor switch. Anyway, a shorted or open circuit heater drive should be flagged as a fault and the output would be disabled to protect the ECU drive in the event of a short.

Trying to think what would continually blow the heater. Excessive heat (fueling?) or voltage I suppose. Sorry to say it, but I do wonder whether the sensor is fine and problem lies with the harness wiring, which might lead to a fault code implying the heater is faulty when it isn't. Might be worth checking out the wiring from EMS ECU connector to lambda sensor to rule the harness out.

Dunno whether that helps.

Cheers

January 31, 2008

Oh blimey, I'm trying to dredge up stuff from my dim and distant past - It's been over 15 years since I did any EMS specific ECU design.
I'm certain we used to monitor lambda sensor heater current, but can't remember whether the heater was PWM (sorry probably to techy), or just a straight power transistor switch. Anyway, a shorted or open circuit heater drive should be flagged as a fault and the output would be disabled to protect the ECU drive in the event of a short.
Trying to think what would continually blow the heater. Excessive heat (fueling?) or voltage I suppose. Sorry to say it, but I do wonder whether the sensor is fine and problem lies with the harness wiring, which might lead to a fault code implying the heater is faulty when it isn't. Might be worth checking out the wiring from EMS ECU connector to lambda sensor to rule the harness out.
Dunno whether that helps.
Cheers

OK

Let's hear more about your dim past then........

September 22, 2008

The heater circuit just gets the sensor up to operating temperature a lot faster to enable proper ECU monitoring - I can't see why it's failure would lead to actual sensor problems at the ECU with regards to fuelling calculations as within a few minutes with a broken heater circuit the sensor should be up to operating temperature regardless.

It could be that the heater circuit in the sensor when failing - is taking the whole sensor out with it (unlikely) or that the stealership is getting you to fork out for a sensor that just has a failed heater circuit BUT the actual important part of the sensor is ACTUALLY still doing its job.

If you know a good auto diagnostician get him to check the actual sensor outputs to tell ya more.

By the way OEM replacements for these sensors can be had for a pittance when compared to Stealership prices - EvilBay has them listed all the time and you can even get good quality platinum replacements for a very reasonable price including shipping from the states. You just need competence in fitting them then is all.