I have been doing research trying to find out how to replace my O2 censor on my 2000 (Orphane) Daewoo Leganza SE.
I can’t make heads or tails of what I have found so far so I have come to the cartalk community for assistance.
1. How many sensors does this make and model have?
I have read about it having both 1 or 2 sensors.
2. When I look to purchase one, I get information on pre and post cad(m). Does that refer to a sensor before and after the cadilidic convertor?
3. Is this a project that can be completed by myself? (with the proper tools: i guess there is a wrench that you have to buy in order to get to some 02 sensors)I am relatively mechanically inclined and do most of my own repairs.
thanks for helping to those that do.
Yes. There are two O2 sensors.
Yes. It requires a special socket to remove/install the O2 sensor.
Yes. You can replace the O2 sensor. The difficulty will be the ease of access the sensor/sensor plug.
Tester
Having some penetrating lube on hand might help too. They can be hard to remove.
You are sure that replacing the oxygen sensors will take care of the problem? You did the troubleshooting as instructed in the repair manual? Aren’t your other questions covered in the repair manual (Haynes, Chilton’s, etc.)?
If you can access the O2s without too much trouble you can simply snip the wire pigtails off and loosen them with a boxed end wrench. They can be reinstalled with the same wrench if need be. I’ve got a couple of O2 special sockets and seldom ever even use them.
O2s are often misdiagnosed and if all of the O2s on your car are legitimately bad then the bigger question is WHY are they bad.
what do you mean by WHY are they bad. I don’t know if they are both bad. The check engine light came on so I took it to a shop to see why. They said it had a bad O/O2 sensor. They didn’t say which one. When I was researching sensors, some people were stating that it is best to replace both of them and that they should be replaced as you get high miles on the car which I have.
The symptons also fit what they were saying, ie. slight hesitation when driving (usually at a consistant speed above 35 - 40 miles an hour) and a decrease in both fuel efficiency and power. All of which I am experiencing.
The point being that O2 sensors are frequently misdiagnosed even by mechanics. Get an O2 code, or codes, and voila; that must be the problem. Not always.
There are many things that can influence an O2 code; oil consumption, vacuum leak, poor engine performance, partially clogged converter, and on and on.
It’s also quite possible this hesitation has nothing to do with any O2 codes. That could be caused by an air leak between the throttle plate and MAF sensor, clogged converter, faulty/dirty MAF, or what have you.
It’s my opinion that whenever an O2 code exists the first step should be connecting a vacuum gauge to test for manifold leaks. Simple and quick.
However, this will not determine a leak between the MAF and the throttle plate. That would have to be a visual, physical inspection.
As to the “why” part of this, O2 sensors can be killed by oil consumption, chronic performance problems, coolant into the combustion chambers, possibly fuel/induction additives if used enough, and even by the aforementioned clogged converters.
For what it’s worth, I’ve been working with O2 sensors since 1977 (SAAB and VW used them 4 years prior to almost everyone else) and have seen very few defective O2 sensors over the years. The few bad ones I have seen were done in by something else.
I’m only saying that when O2 codes exist that one should not automatically assume the O2s are at fault.
I hope some of that helps anyway.
So what would you suggest doing. I will need to take it to a shop to have all the things you spoke of checked out. Do I ask them simply to check the things that you mentioned?
I am concerned because this vehicle is my everyday driver and at least the O2 censors seemed to be an inexpensive fix (single dad working on a limited budget)
It sounds that mechanics can be lazy at times if they fail to diagnose the problem in more detail. Knowing this, I will not be taking it to the same shop.
Coolant in the combustion chambers, would you be able to visually see that when you checked or changed the oil? I had them preform an oil change while it was being checked out and they didn’t mention seeing anything.
How would I determine oil consumption? Simply continue to check to see if it going through more oil than it should?
As far as chronic performance problems, my first thought when I felt the hesitation was a bad valve. I had an old rabbit years ago that I felt a similar thing when I was driving and it turned out needing a valve job. Would not the computer they use to diagnose the check engine light have stated that if it was a valve issue?
I appreciate the information so far, but any additional help you can offer, obviously will be greatly appreciated.
I almost forgot, what is the MAF?
The MAF (Mass Air Flow) sensor is a widget that measures how much air the engine is pulling in. A faulty or dirty MAF can cause a hesitation although I’m not saying the MAF is the problem here.
The MAF is usually located in the intake tract between the throttle plate and the air filter.
Unless your oil consumption is along the order of a quart per 1000 miles or whatever and has been a chronic problem I would not worry too much about that. Same for any coolant problems. If there’s never been any overheating episodes, head gasket failures, etc. or coolant loss this should not be a problem either.
There are a number of problems that can exist in which a computer code may not be set and the valve problem you mention is one of those. However, if a valve problem (compression fault) exists then the engine should have a rough idle or a stumble at idle.
As to diagnosis of problems, there is kind of a Catch 22 there. It’s unfair to the car owner to guess and throw parts at the car on the one side.
On the other side, there are a number of diagnostic steps involved and things like this take time. Since a mechanic gets paid for what he does you can see that if he gets involved in performing a number of diagnostic steps for free his paycheck will suffer.
In theory, a guy performing driveability work in a shop could wind up doing diagnostic steps for free almost all day long. (And believe me, it happens. A lot.)
A tech should be astute enough to get around a few things and be prepared to eat a little free time to make sure they’re on the right track but that’s a real iffy premise.
This is one reason I mention the use of a vacuum gauge. It’s a cheap tool, can be connected in seconds, and once you learn to read one properly it can reveal a lot of things without having to dig as deep as you might normally need to.
I’m not saying the O2 sensors on your car are good; just that I’m not convinced they’re the problem behind the symptom.
You might have a parts house like AutoZone, Checkers, etc. scan the car and post the exact codes back here for discussion. They will do this for you free.
It could likely be iffy as to whether the problem could be elaborated on any further but it’s worth a shot.
For what it’s worth, all of my vehicles and my 3 grown childrens’s vehicles have seen a lot of mileage over the decades and we have never needed to buy an O2 sensor for any of them except in one instance. In that case, a wrench slipped while I was doing routine maintenance, tapped the O2, and cracked the porcelain insulator. It was still working but I replaced it just to be sure.
I guess that’s what amazes me a bit on this board; the number of posts about O2 failures.
Thanks again for everything.
I don’t think that oil consumption is the problem. I have to be honest, I don’t think it even goes through a quart every 1000 miles.
As far as coolant, there hasn’t been any overheating episodes, head gasket failurs. There is a slight coolant loss, but I believe I have a slow leak somewhere. I recently noticed a spot on the concrete near the front right side of my car when it is parked. I rubbed it with my fingers and it did not smell of oil. When I got on the ground and notice two little drips of coolant on the undercarraige. So do have to add coolant periodically, but only something along the lines of every three to four weeks and that is only to refill the resevior.
It does not idle rough on a consistant basis. Usually not at all. I might be picky and feel that it idles rough from time to time, but I usually remind myself that it has 136,000 miles on it and cars that old don’t run as well as new cars.
I will look into a vacuum guage. I assume that if I get one at Autozone or some place like that they would show me how to connect it. As far as reading it, where can I go to learn to do so correctly.
Thanks again.
I wished that I could be of more help but without car in hand it’s pretty difficult to be precise since there are so many things that could cause a hesitation at that speed.
The vacuum gauge suggestion is made only because I’m a huge fan of using one and sad to say many, or most, mechanics do not use them.
Since you do not have an oil consumption problem or rough idle I’m inclined to think the engine is fine and the problem is comparatively minor.
I would add that if you get a vacuum gauge do not always place all of your faith into what the instructions may state. Some of those instructions may state that you should have 22" of vacuum at idle, etc. and this is very seldom the case. It depends on altitude, type of car, engine wear, barometric pressure, etc. and around here 17-19" is normal. (1100 feet elevation over sea level)
And the reading at idle should always be rock steady.
ok, i am back again after all the snow fall and bitterly cold weather. didn’t promote too much car work.
anyway, took it to another shop last weekend and after being there two days (they had told me that they could do a more indepth troubleshooting regarding my problem) they informed me that they didn’t have the proper terminal to hook up their computer to my car and that they didn’t have the codes for a daewoo either.
the check engine light is off now, but the hesitation has gotten worse. now i am experiencing it at times at lower speeds and at start up, when accelerating from a stop light.
i purchased a vacuum gauge but now am struggling to find out where to hook it up. the car has an aftermarket air intake. (the air filter is actually located behind the passenger front wheel well with a metal tube running to the top of the engin). i was in a hurry when i bought the gauge and didn’t have time to talk to the sales person and figured there would be instructions in the part’s package. there were, but then are not helpful. make it sound much easier to locate. lol befor i head to a shop to ask, just thought i would try here first.
The brake master cylinder operates off vacuum. You could use that hose. Use (almost) any hose which comes off the intake manifold, for a vacuum source.
The hesitation might be a fuel control problem. Have you changed the fuel filter, recently? Air filter? How about checking the fuel pressure at idle, and at 20000 rpm with the transmission in DRIVE?
The spark plugs might be a problem. Pull them out and examine them.
Before you do ANYTHING, check the electrical connections to the sensors…9 times out of 10, problems like this are a bad connection…