1Az-Fse Oxygen Sensor Problem

[MadButcher]

Hi guys, need an advice from someone more experianced. My 2004 Ave 1AZ-FSE (direct injection) has 4 oxygen sensors, 1 was faulty and car reported it by warning light for like 1.5 year or so. All the time car was running perfect, really fast and agile, with consumption of 8-9 liter / 100km.

I finally decided to change the faulty sensor and followed my mechanics advice to buy cheaper Denso sensor, which was supposed to be exactly the same as from Toyota just with different connector. They cut connectors and climped new sensor to old connector.

Now the car doesnt report any errors, but dont want to accelerate. It goes perfectly below 3000 rpm, but every acceleration above that and every take-over is nightmare. Also sound is bad then, I can hear something is wrong in engine. Consumption is 8.5 liter / 100km, so no benefit here.

What we tried to do with another mechanic was to unplug this sensor (+ another one in the line), which supposed to force engine management unit to exclude oxygen sensors from engine control and use "standard fuel map" recorded in its memory.

Now the car is exactly like before, fast and agile, nice sound - so I am sure that my engine was managed without oxygen sensors for cca 18 months.

Now the question - is there any real danger of damaging the engine, if engine is left without these oxygen sensors using only "standard fuel map" without corrections as it doesnt have data back from sensors?

[MadButcher]

For those who may be curious: this has been solved.

When I saw that after disconnecting lambda (oxygen) sensors car goes OK again so there is nothing wrong with engine itself, I was sure the problem is caused either by new lambda sensor that can be faulty, or by wrong translations of correct lambda sensor data in engine management unit (EFI?).

The easiest way how to recognize which assumption is correct was to clear EFI memory. The assumption here was that EFI saves some correction data taken from real life ("self-mapping" - drivers style, rpm, how heavy you are on accelerator etc., also data from oxygen sensors and maybe some other information), and that there can be wrong self-mapping data stored from time when EFI ignored wrong lambda sensor which can cause all those issues now.

I pull out EFI fuses for couple minutes to clear EFI memory and to initiate standard fuel map, connected all lambda sensors back, started the engine, and found that everything was fine. No engine warning light on dashboard, car went OK in any rpm, consumption 8.0-8.5 liter/100km.

In the beginning I could feel very little resistance, but obviously self-mapping worked quite well and EFI learned fast so after 2 tanks of fuel all is perfect now. I have fast and reliable car again, with fuel consumption that is mirroring my driving style.

I am not an engine expert, so some of my assumptions or evaluations can be far from reality, but maybe this will help to someone.

[perdaniel]

It is good to hear that you don't have any more problems with the oxygen sensors. It seems to me that they are weak points in this engine. When the sensors on my car have gone it has always been the pre-heating curcuit that was faulty. Was it one of the upper (pre cat) or lower (post cat) sensors you changed? Do you know what the error code was?

[MadButcher]

It was that sensor which you can see disconnected on right side of picture, grey socket - I believe that is pre cat. I dont remember error code but will find it later at home, there was exact specification of which sensor that was.

[waqar_lionheart]

Hi MadButcher,

I run a 1zzfe 2001 1.8 vvti (still a non oil burner). My car ran with faulty o2 sensors for many years before I bought it. This came with full service history with previous owner not replacing these sensors. Any ways, I did them soon after I bought it last year. It has no errors but ran like crap unlike before (its definitely fuel/air ratio). I must say if what you are saying works, then you have helped me fix one of my biggest gripes with this car.

best regards,

Waqar

[MadButcher]

Waqar,

I am really looking forward to see whether this will work for anyone else.

If you want I can look in the User Manual tonight and give you names of all fuses that I removed for resetting. There were 4 of them that I thought could be involved, of course I am not sure wheter all of them needed to be removed or not.

[waqar_lionheart]

I have read extensively about this and generally yes, it should help. i am aware of the fault codes as having suffered with eml for some time when i bought the car, I read extensively about how a car works and now can say that am an intermediate kind of will fix with a look up mechanic. However, it will help immensely if you could tell me which fuses you pulled. i have been told to remove, efi and ecu fuse. this should help. Or disconnect the Battery for a while. thus achieving the same result interms of ecu mapping but much :).

Regards,

Waqar

[MadButcher]

So according my records it was error code P0156 "Sensor Circuit Malfunction (Bank 2 Sensor 2)" which should be post-cat.

Waqar, these are fuses that I pulled out:

EFI

IG2

EFI NO.1

EFI NO.2

EFI NO.1 and EFI NO.2 fuses are located in separated fuse box in engine boot in Ave T25, together with ABS and VSC fuses. You have T22 I think so not sure whether it is the same for your car or not.

And you are absolutely right about disconnecting the Battery, of course it will have the same effect on EFI, but I dont know what other systems will be affected as well and my mechanic advised me not to disconnect the Battery just because that.

Cheers.