Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

O2 Sensor & Check Engine Light

The check engine light in my Rabbit came on in January of 2011, just after I’d had it inspected. After hitting a dead end with the local VW dealership regarding diagnosing the vehicle (they wanted to charge me $75 to plug it in, but then said if the car was running fine, I could drive on it), I opted to drive on it. At a later date, I had the code read elsewhere and discovered it was the O2 sensor. After doing some research, I discovered the emissions system is covered under an 8-year, 80,000 mile warranty. My car was sitting around 72,000 when I realized this. As such, I chose to have it fixed.

Dealership found a blown O2 sensor and corroded wires. They ordered the part and called me to come in TWO weeks later. They repaired the wire, but had (likely) ordered the wrong sensor, so I had to go back in again. Brought it back in, they replaced the sensor. 2 miles off the lot, the light came back on. Took it back the same day and they found (and fixed) more wire corrosion. About two start cycles later, the light came back on.

At this time I chose to take the car down to another dealership. They spent 6 hours with it, repairing more spots of corroded wire, but still couldn’t get the light to stay off. They theorized that the sensor had been blown so long/so badly/repeatedly that the related sensor for the ECM was now confused. Made plans to bring it back two weeks later to have the ECM replaced. Approximately 4 to 5 start cycles and less than 100 miles later, the light is now back on.

Now, I know that the rear O2 sensor monitors the levels for the catalytic converter. I’d be happy to continue with my light on, except that it shuts that O2 sensor off if it thinks there’s an issue. Eventually this is going to affect my mileage even more than it already has. My thinking is that despite what the codes say, it is now the catalytic converter (something I dread to have to pay for). Are there other theories regarding this?

Perhaps a new cat is covered under the emissions warranty? Why would a 2011 car have these issues with “corroded” wires? Seems way to new a car for this sort of problem. Are they showing you the wires and where they are corroded? Perhaps these bad wires is just a cover up story for the fact they have no clue what is going on?

More info please? What year is the Rabbit? Gas or diesel? Miles on the car? Did you buy it new or used?

It’s a 2007 2.5 liter gas engine. As stated above, there were 72,000 on it when I started pursuing the issue. There are now about 77,000 on it. Bought it brand new.

I saw both the O2 sensor and sections of corroded wire. In summary, it wasn’t a pretty picture. Yes, the bigger issue is how wires in a young car (no collision history) became corroded, but for right now I just want the light off and the system fixed.

I have confirmed with the dealer that the converter should be covered under the extended warranty.

Basically just keep taking it back until the dealer finds and resolves the problem. It is an inconvience for you but it is also a lingering problem for the dealer. They should be motivated to fix the problem and not have to see you again for awhile.

It sounds to me that there has been some needless expensive repairs done. I doubt very much the ECU needed to be replaced. The CAT may be damaged since you let the O2 sensor problem go on for some time. It would help to know what codes are now being set. You can purchase your own code reader or scanner for not much of an investment.

I just went to a local mechanic to get the latest code reading. Now I’m getting that it’s the Idle Air Sensor. Could be they forgot to plug it in when they replaced the ECM, but I would think if that had been the case the light would have come on sooner (and they’d’ve caught it at the dealer).

And yes, it’s possible that the ECM didn’t need replacing, but it fixed the O2 code when nothing else would.

 That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Your post is lengthy and without poring over every word in it I see so many misconceptions it’s difficult to say what’s gong on; and no codes were provided either.

First off, charging you 75 for a scan and diagnosis is a legitimate procedure. A shop and mechanic can scan cars 6 days a week for free but that doesn’t keep the electricity on and food on the table.

You are incorrect about the 8 years/80k miles emissions warranty. That warranty only covers the ECM and converter, not everything else.

O2 sensors do not “blow” so that’s either a misinterpretation or someone has used a pretty lousy descriptive term to describe the problem.

You’ve opted to drive over a year since Jan. of '11 so this brings up the point about other maintenance on the car regarding spark plugs, filters, and so on.
Most converters (if they are faulty) do not die natural deaths; they are killed by something else.

@Ok4450 - Thank you for attacking me. I really appreciate it. Makes me feel great and like I don’t know a damned thing about my car and how it runs.

Yes, I know driving around with the light on for almost a year was a poor decision. My car was running fine and I actively made the choice to put it at risk because I did not have the money at the time for the repairs. It still went in for regular maintenance, despite choosing to avoid what I thought would be a costly repair.

And yes, I know that charging money for a diagnosis makes sense. All I wanted them to do was tell me the code so that I could make an estimation of the possible costs to fix the problem. It takes less than five minutes to plug a machine in and get the numbers.

And perhaps you thought I used a bad word by describing the sensor has having “blown,” but it was the best descriptor I could come up with for the damage I saw. The entire sensor had corroded to the point that portions of the internal plug had broken off. It genuinely looked as though a short caused the internal pieces to “blow” off.

That said, I postulated that my converter could have a problem now because I elected to drive around for a year with a malfunctioning O2 sensor. I recognize that any problems could be entirely my own fault due to the stress I put on the car.

And as far as your statement regarding the warranty - you’re just nitpicking at this point. The O2 sensor is considered part of the emissions system by VW and VW agreed to cover it under the extended emissions warranty. If you’re going to post on here to help people out with their issues, consider doing it in a polite and helpful manner. Being rude and degrading the way we describe our issue only adds to an already stressful situation.

OK4450 was IMHO only trying to inform you, not attack you. There are misunderstandings present in your post that make trying to assess the problem difficult.

Does it specify on your copy of the shop order which O2 sensor was bad? Catalytic converters are damaged only by the catalyst being coated with exhaust byproducts or by damage to the ceramic substrate. If an upstream O2 sensor is bad and causes rich operation, the resulting carbon can coat the catalyst and destroy the converter, and if raw gas (unburned bydrocarbon) is getting into the converter that can “backfire” (combust) and damage the ceramic. Have you experienced any “backfiring”?

If it was the downstreat O2 sensor that was bad, that cannot destroy your converter. You said that the shops indicated that the wires were corroded, but I find myself wondering exactly what the shop order says. Normally the oxygen sensor will “corrode to the pipe”, but the wire corrosion thing has me wondering. That’d be unusual as described. Any shop finding a corrsion problem on a sensor would simply replace the sensor.

An oxygen sensor cannot “confuse” an ECM. The ECM has a “fixed” program that compares the upstream signal with the downstream signal. If they’re not sufficiently different, it trips the light. The oxygen sensor signal in no way can influence the parameters of the program.

Know too that the CEL does not “shut off” the oxygen sensor. The sensor keeps sensing and the ECM keeps monitoring its output.

There are, I believe, some misconceptions and miunderstandings in your post. As well as some descriptions of shop actions that make no sense due to these misunderstandings. Did the first shop tell you yo needed a new converter? Did you tell them that you did not want to pay for one, and then they tried cleaning the wiring conections for you, whoch didn;t work? Did you then go to the second shop and repeat the process?

I mean no disrespect by asking these questions, I’m just trying ot get a clear picture of the problem.

I’m not attacking you at all; only pointing out that your post appears to show a number of misconceptions.

To address one, let’s take the emisssions warranty one that you mentioned finding on the net. In your original post you did not mention an extended warranty. Some extended warranties will cover an O2 sensor problem, others will not.
The Federal 8/80 warranty will NOT cover O2 sensors for that length of time.

Regarding the 75 dollar fee they were going to charge you let me ask this. Do you sincerely think that the service advisor should write up a repair order, the car brought into the shop for a 5 minute scan, and then handed back to you free of charge?

I didn’t see any “attack” either.

But I will go so far as to say that whatever you know about your car you don’t nearly enough. There is no code that can tell you about an O2 sensor being bad. Nor a code that will report on the idle air “sensor” (though I suspect you mean “valve”). This is common misunderstanding of codes.

The codes look like “P1234.” If you want some clearer help report the exact codes.