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smayoo

Oxygen Sensor Replaced, But Engine Warning Light Comes Back

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Hello, everyone! I'm new to this forum and I've tried to find a similar topic before posting a new one, but none I've found gave me sufficient detail, so there... :)

I own a Carina E Estate with 1.6 16V 4AFE engine, manufactured 12/1995, with about 130.000 miles. Thanks to earlier posts in this forum I've managed to positively diagnose my check engine warning light (that was permanently on for the last year or so) to a faulty oxygen sensor. I did suspect that even before, since the average consumption went up about 20% (although the eco-test was fine all the time).

Anyway, since the original replacement part at the local Toyota dealer here in Croatia is way to expensive for a car of that mileage and age, I ordered one from E-bay (declared as Denso OEM part specifically for this make and model, by the part number). The sensor came with original connector, there was no need to cut and re-connect any wires or anything like that. The replacing procedure took about 2 minutes and I replaced the sensor myself.

Now, before replacing, the engine warning light never at all went off. It was on before starting the engine (which is normal), and it was permanently on after starting the engine.

After replacing, the warning light goes off after starting the engine, but it then goes back on after about a minute or so (regardless of whether I actually drive the car, or just leave it running in neutral). That is - when the engine is cold. When the engine is hot, than it takes less than a minute - maybe 10, maybe 20 or 30 seconds.

Does anyone have an idea what might be the problem? Is there maybe a blown fuse protecting the sensor heater circuit that I should also replace? Or something like that? Or is there maybe a callibration procedure?

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There are 2 different 1.6 lit engines. Are you sure you got the right one? If you have the leanburn version of the engine you can have the same sensor as the 1.8 liters engine 7A-FE. I bought a second hand sensor from a 1.8 liter Carina earlier this year and it works just fine on my 1.6 lit leanburn engine. I don't remember wich part number it was, but double check that you have the same numbers on your old sensor and your new sensor.

You can also use this site to search for part numbers www.toyodiy.com.

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It's a 16 valve 1.6 engine (4A-FE), so-called "lean-burn". The part numbers match. I don't know about a 1.8 liter engine type, but I have a new sensor, made by Denso, with matching part number. Since, after replacing, the warning light does go off (and then later it goes on again), I'm thinking that the sensor is not faulty, but that there's some other problem.

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Wich fault code do you get now with the new sensor fitted?

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Again 21 (oxygen probe), but it acts differently (it doesn't light up immediately, but after a minute, as I wrote). I'm wildly guessing that before, with the old probe, the probe's heater was shorted out, but now maybe it's something else? Maybe the heater doesn't get the supply, or maybe the heater is fine, but the measurement is out of range, or something? :huh:

I asked the probe supplier about it. They suggest that maybe I should reset the EFI. Does that make sense? If it does, how do I do it?

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You pull the EFI fuse for a while (15 sec if I remember correctly) to reset the memory.

Remember that the faultcode might also mean that the ecu doesn't get the correct signal. A fault code doesn't mean that a sensor is faulty the fault might also be somewhere between the sensor and the ecu.

If you are more than 100% sure that the new oxygen sensor is ok. You have to have a closer look at the wiring from the sensor to the ecu.

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Thanks for your patience. :)

Which EFI fuse exactly is that? I looked in my owner's handbook and there are 5-6 fuses all over the car that are marked "EFI" along with something else (signal lamps, lights, radio, ...) and there is one, under the bonnet, which is only EFI. Is it that one?

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Yes, it is that one. Pull it about 15 sec. Then you have resetted the memory of fault codes. Then when the check engine light goes on it is a new fault read wich code you get then.

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