1 of many O2 sensors faulty. will vehicle still work?

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Batman

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#289562 13-Sep-2021 11:13

say a car has many o2 sensors - i think 3.

if the one closest to the engine is faulty, is that the main o2 sensor?

i don't suppose the car will know to use the other oxygen sensors to monitor air fuel ratio?

(actually i know it doesn't because i just bought an obd reader and afr = open loop)

car works fine otherwise

the local toyota dealer has no clue, they say they don't fix imports. i think i'ma need to find another mechanic who can tell me what's going on

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#2777264 13-Sep-2021 11:21

The other sensors aren't there as spares - it's not a matter of using a backup one. In general, there would be a sensor for each exhaust manifold (so 1 for a straight 4 cylinder engine, 2 for V6 etc) which measures the ratio for that cylinder bank. Some vehicles will then have a further one after the catalytic converter to measure if that is working correctly.

EDIT: Think of them like tires - if one goes flat, you don't just keep on driving. They all work together as a system.

duckDecoy

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#2777270 13-Sep-2021 11:39

My Toyota Avensis has 4 O2 sensors and i have replaced 2 at hideous expense each. Apparently it is a really common fault.

I regularly get the engine warning light on and the code is the O2 sensor (one of the other 2 will be playing up now). My mechanic said just live with it, he doesn't see it causing long term issues and his comment to me was that I will get slightly worse fuel economy but not much else.

EDIT: I am not mechanically minded in any way so I assume his advice is correct. But if not someone will likely reply.

Batman

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#2777284 13-Sep-2021 11:53

duckDecoy:My mechanic said just live with it, he doesn't see it causing long term issues and his comment to me was that I will get slightly worse fuel economy but not much else.

that is exactly what i'm getting. basically the car works 100% normally. but it's running on open loop which means it burns a bit more fuel. that doesn't worry me i hardly use it. but it's the check engine light that annoys me lol.

i've found where the downstream sensors are. runningman suggests i should have 2 upstream ones as it's a (very very very tightly packaged) V6.

i guess i need to identify where exactly it is and if the vehicle ever gets stripped to that area i will get them to replace it.

wellygary

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#2777289 13-Sep-2021 12:00

Batman:

that is exactly what i'm getting. basically the car works 100% normally. but it's running on open loop which means it burns a bit more fuel. that doesn't worry me i hardly use it. but it's the check engine light that annoys me lol.

Batman

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#2777355 13-Sep-2021 12:37

well if i could get under the plastic shield on the dash i would!

it may please you to know that a rabbit sacrificed its life in detaching and misplacing a bolt on the wheel arch fender of this car and it's now held together by the use of a single paper clip for the last 5 years.

snnet

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#2777362 13-Sep-2021 12:45

I had this on a jeep and it caused my engine to lose power constantly and there was always a pressure buildup that popped the air intake filter cover off - very annoying for something that cost $5 to replace

gbwelly

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#2777554 13-Sep-2021 14:35

snnet:

I had this on a jeep and it caused my engine to lose power constantly and there was always a pressure buildup that popped the air intake filter cover off

Aren't Jeeps like that from factory?

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gbwelly

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#2777574 13-Sep-2021 14:40

Batman:

i think i'ma need to find another mechanic who can tell me what's going on

I've never seen a problem with the wiring of an O2 sensor between the sensor and the ECU, it's always been the sensor itself that has failed. If you can find out the part number for the O2 sensor it's usually just a case of buying one, and installing it. Where it gets exciting sometimes is the extraction of the old sensor. I'd suggest spraying the bung with WD40 a couple of times in the days before the extraction.

tripper1000

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#2777621 13-Sep-2021 16:11

Just take a peek in there and make sure it isn't an silly little problem like it is unplugged.

I've replaced a couple of O2 sensors in my day. If you are handy, it is cheaper to replace them yourself than pay someone, unless it goes south and the old one gets stuck in. If they turn a little then bind up, don't undo them harder. Instead do them back up and try again - over and over. By working them back and forth you can slowly work the rust out of the threads. Many jappa's have stainless exhausts, which is great for longevity but makes it hard to drill out broken bits and retap the threads.

One O2 sensor I replaced had the wires ripped out of it, and on the other, the internal heater had failed so it took ages to get hot enough to go into closed loop mode.

Without them the engine should go into a 'safe' rich mode, but the excess fuel can work the catalytic converter harder and/or make more carbon with the associated fouling issues. You also lose a layer of insurance/assurance without it - if the engine starts running lean (clogged fuel filter, failing fuel pump, running high ethanol fuel, failing/phucked-with boost sensor/controller/waste-gate) the computer wont know and you can end up melting valves and pistons. So while everything else is working properly, yes the car continues to go fine, but once a second thing fails, all bets are off.

FYI the down stream O2 sensors are looking to see a different/more stable reading that the upstream O2 sensors. This signals that the Cat is working OK. If the Cat stops working then the ECU will see the same(ish) reading on upstream and down stream sensors and knows to throw a fault code. The downstream sensors can't be used as a backup for the upstream sensors because the whole point of the CAT is to burn the unused fuel/combustibles/emissions, so you will (should) always have less O2 to detect after the CAT than before it - that means the reading does not reflect the engine Air-fuel ratio which is the job of the upstream sensor.

Batman

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#2777701 13-Sep-2021 16:47

Thanks that's a very detailed explanation. It's very tightly packed. I can't see where it is from the top or bottom. But that's my next mission. Only just bought the obd reader.

The dumb dealer had my car for 2 weeks and said I need a new engine. I said I'm not paying them a cent. Got a bill for $16

gregmcc

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#2777706 13-Sep-2021 17:01

Batman:

duckDecoy:My mechanic said just live with it, he doesn't see it causing long term issues and his comment to me was that I will get slightly worse fuel economy but not much else.

that is exactly what i'm getting. basically the car works 100% normally. but it's running on open loop which means it burns a bit more fuel. that doesn't worry me i hardly use it. but it's the check engine light that annoys me lol.

i've found where the downstream sensors are. runningman suggests i should have 2 upstream ones as it's a (very very very tightly packaged) V6.

i guess i need to identify where exactly it is and if the vehicle ever gets stripped to that area i will get them to replace it.

You will find that if the data from a O2 sensor if not what is expected the engine computer will fallback to a pre-set generic value to keep things going, your fuel consumption may be worse, if it's an auto transmission the shift pattern may alter slightly, call it a 'default' setting if there is a failure.

I'm assuming it's set a check engine light and you have plugged in a OBD reader.

Replacing an o2 sensor isn't a big deal, but I don't think you can reset the check engine light from these, you need a proper scan tool to do this.

Keep in mind an open loop may not be a faulty sensor, it could be a broken wire.

Batman

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#2777723 13-Sep-2021 17:14

Thanks all

snnet

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#2777728 13-Sep-2021 17:19

gbwelly:

snnet:

I had this on a jeep and it caused my engine to lose power constantly and there was always a pressure buildup that popped the air intake filter cover off

Aren't Jeeps like that from factory?

Where were you to tell me that when I was buying the abomination

k1w1k1d

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#2777791 13-Sep-2021 18:08

My work supplied Toyota Avensis pops up O2 sensor errors when it feels like it. I just clear the code and carry on. It has been doing it for a few years without any drivability issues.

Toyota dealer that services it says it is a common fault with them.

snnet

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#2777841 13-Sep-2021 21:19

k1w1k1d:

My work supplied Toyota Avensis pops up O2 sensor errors when it feels like it. I just clear the code and carry on. It has been doing it for a few years without any drivability issues.

Toyota dealer that services it says it is a common fault with them.

Apparently if they get a bit grubby it can cause intermittent problems

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