O2 sensors are my pet peeve...

BMR BOY · 08-24-2005, 07:23 PM

Ok guys. Here's a new one for you: I have a 1996 328i with 67,300 ORIGINAL miles on it. My check engine light came on about 2k miles ago, but goes out for 3 weeks, then comes on for three days, then back out for another week. I pulled the codes with an Auto-Xray 5000, and it said "o2 sensor, bank 2; sensor 1; curcuit slow response." So, being in the know, I called Auto-Xray, and demanded an explantion. The guy calmly said, "Oh, bank two means cylanders 4-6 (since thats a different exaust, therefore requiring a different o2 sensor), and sensor 1 means pre-cat." That made perfect sense. Pretty easy stuff. I've done a few o2 sensors in my day, shouldn't be anything unusual. So I call my buddy, a BMW technician with the "curcuit slow response" question. He tells me it's a common problem for them to pop that code early, along with an intermittant light, signaling they're about to go caput. He finishes with, "That's what sucks about getting close to 100k miles; those sensors all go bad pretty close to the same time, and it's about $800 to get four new ones." WHOA! 100k? I'm at 67, I said back. These are supposed to last 100k? Yup, he said. So I make some calls (since I'm in the know), and get a Bosch o2 sensor for $120, which is cheap considering the $200 shelf price. So I install it in my apartment parking lot, which is TOTALLY against the rules, and I expect that little annoying light to shut off when I start up, as well as my 8 mpg stint to go away. NOPE! Light stayed on, bad gas milage continued. I quickly rescan with the auto xray, it again pulls, "Bank 2; sensor 1, curcuit slow response" DAMN. Now what?
BMR BOY

blkongry · 08-26-2005, 07:12 AM

Oof, you've got the OBDII, so you've got 4 O2 sensors, huh? ('95 was the last year for the OBDI). So, if you believe your ECU, and it is the bank 2, sensor 1 circuit, then I'd say it's some sort of a connection issue. You may have some corrosion and a bad contact somewhere. One way to tell is to swap the two pre-cat O2 sensors and see where the code goes. If it stays on bank 2, sensor 1, then you know it's not the sensor and it's somewhere else in the circuit (plus you'll probably want to hang on to that other sensor that you took out, because it's probably not bad).

Yeah, isn't apartment parking lot repairs fun?? You're under your car swinging a wrench, all dirty, and people are meandering all around you. I used to wait till Sunday morning for maintenance, that way I'd ensure no complex management or staff would be around. Although, I felt out of place with all these people dressed nice for church and I had busted knuckles and my grubbies on

Hope you find the glitch triggering your warning light, and I hope it's a straight forward fix.... then you can get out of that 8mpg range... sheesh. Let us know.

Wayne 962 · Wayne 962's Garage

Swapping the sensors back and forth is smart. I would also get one of those ODBII readers for your laptop and see what the codes and signals read while running the car.

-Wayne

BMR BOY · 08-28-2005, 09:52 PM

So how about this: instead of fighting those crappily placed o2 sensors, how about I just swap the plug ends, and see what code pops out? I think that would serve the same purpose. I have used the auto-xray 5000 while the car is running, and I can't remember offhand how many volts each o2 sensor was putting out, but I can rescan it and check. Thanks for the help guys, I really appreciate it. I've actually been riding my bicycle to work, and utilizing public transportation so that I can save money by not driving at 8mpg. Fortunately, I just got a new job at a car dealership, who ALSO owns a BMW dealership, so I get the hookup on parts (cost) and service. So I'll try a thing or two and let you know how it goes. Other ideas are always welcome. I appreciate it greatly!
BMR BOY

blkongry · 08-28-2005, 10:08 PM

Yeah!! If you can swap the plugs, that's the easiest way to go. Let us know what you find out.

PS, congrats on the new job!!

scintaar · 08-30-2005, 07:13 AM

Just a thought... did you reset the ECU after changing the sensor?
From what I've picked up, if you don't reset, the ECU keeps the damn fault code and won't switch the light off. It also stays in "safe" mode until reset.
I could be wrong.... but as I said, just a thought.

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by scintaar
Just a thought... did you reset the ECU after changing the sensor?
From what I've picked up, if you don't reset, the ECU keeps the damn fault code and won't switch the light off. It also stays in "safe" mode until reset.
I could be wrong.... but as I said, just a thought.

Right - you do need to clear out the codes...

-Wayne

BMR BOY · 09-01-2005, 10:25 PM

Yes, I did clear out the codes with the auto-xay, however, when I changed my ex-girlfriends o2 sensor in her '96 318ti (which the light popped on at 99.8k miles), the code was automatically reset, and the car performed like normal. I don't understand it at all. I reset it like last wedensday, and it still hasn't turned on again yet, but I'm still getting 8mpg. Also, my buddy was behind me in his m3 and said when I got on the accelerator, he almost choked on the smell of gas from being behind me.
It's only a matter of time before it goes to the dealer for a lookover, unless I find something.
BMR BOY

blkongry · 09-01-2005, 11:09 PM

Sheesh... sounds like the O2 sensor isn't working at all, or giving totally skewed readings. Do maybe have some melted wires somewhere?? Grounding out somewhere? Try getting a multimeter, set it to resistance (ohms), touch one wire to an exhaust pipe or the frame, then plug another end into each prong of the O2 sensor. If one shows no resistance, or near 0 ohms, then it may be a short, which would make sense. I'm starting to think it's not the O2 sensor at all, but rather something in the wiring and connection. Even when O2 sensors start to go bad, they don't cause your mix to totally freak out to that extreme.

blkongry · 09-01-2005, 11:11 PM

Oh, you might want to even try disconnecting it and see what happens and how it drives. If it drives better with that sensor disconnected than with it connected, then something is shorting and going weird, 'cause that just ain't natural ;-p~~

Wayne 962 · Wayne 962's Garage

So, it's getting 8 mpg and not punching out any codes? Very odd...

Just because the Check Engine Light doesn't come on, doesn't mean it's not pulling codes - not all code failures trigger the light...

-Wayne

BMR BOY · 09-02-2005, 03:13 PM

Well, it's technically still giving the code, but the light isn't on(since I turned it off when I reset it). However, the fault (bank 2, sensor 1; curcuit slow response) is still in the cars memory. I would try a few things, but I just got called up today to go to Louisiana for the flood relief. So I'll put my car o hold for a month or two, and we'll work some more when I get back. I have no idea why the Oregon National Guard is going, but I guess it's not optional. Talk to you all later, and I really appreciate all the help. Supertack, your "present" is going in the mail tomorrow I believe.
BMR BOY

blkongry · 09-09-2005, 07:43 AM

Good luck over there in LA... it's looking like a nasty, dirty, unhealthy job to clean up the mess. Hopefully you won't have to stay long. We'll figure out that sensor issue when you get back.

BMR BOY · 10-02-2005, 10:30 PM

I'm back!
Good news guys! I'm actually back from Louisiana, after surviving both hurricane Katrina and Rita. Anyway, while I was gone, my manager from the BMW dealership called my friend and had her drive my car to the dealership to be looked at while I was gone. This was two weeks ago! The technicians are looking furiously for something wrong, and are coming up empty handed. They're currently looking into replacing the catalytic converter on the rear three cylanders. And the total bill so far? $0.00. I guess it pays to help out the country when it needs it. I'll keep everyone posted on what they find. I'm ready to ditch my Buick Century for my Driving Machine RIGHT NOW! Thanks guys!
BMR BOY

Wayne 962 · Wayne 962's Garage

Let us know what they find out!

-Wayne

BMR BOY · 10-13-2005, 12:00 PM

Forgot that I finally got my car back! Lol. Actually, I'm just spending more time behind the wheel than at the computer. Anyway, the BMW technicians replaced the second (post-cat) sensor as well, and the car seems to be running fine. The check engine light is not on, but I haven't scanned it personally. I got a copy of the invoice for the work on my car; 4.5 hours of technician time at $145 per hour: $652.50. One Bosch premium oxygen sensor, pt #13884: $199.99. Total: $852.49. Billed to? Dealership. Nice. Thanks for the input though guys. Great to have my car back.
BMR BOY