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Old 03-05-2002, 12:13 PM
Posts: n/a
Just failed emissions test. Bad O2 sensor?

My mom's c220 just failed the emmissions test (I should have known it was going to because of the "check engine light").

My best guess is that one of the O2 sensors is busted, but I'm not sure which one. When I went around to get it OBDII scanned, and all the shops wanted 65 bucks just to "diagnose it". I can't believe they want $65 for a 4 min job.

Anyway, the car has 40k miles on it. Is it normal for an O2 sensor to bite the dust this soon? I replaced the one in my jeep after 100k. Also, my jeep only has one sensor (before the cat).

Why are there 2 sensors in the c220? Can I assume that the precat is the one I need to change b/c its the one that controls the fuel mixture? (I'm fairly certain the sensor is stuck open and causing the engine to run rich)

Can it be anything other than the O2 sensor?


Just had another idea- is it the same part# for both O2 sensors?
Maybe I could replace one and if the light stays on, just switch it.
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Old 03-05-2002, 01:25 PM
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what were your emmission readings?
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Old 03-05-2002, 07:43 PM
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"Explain rejection fully: HC and CO levels high

High Speed: standard / current reading
HC (ppm): 220 / 232 fail
CO (%): 1.20 / 5.60 fail
CO2 (%): 11.8 (current)
O2 (%): 15.9 (current)
Diloution: >6.0% / 17.4%

Low Speed: standard / current reading
HC (ppm): 220 / 349 fail
CO (%): 1.20 / 7.86 fail
CO2 (%): 10.4 (current)
O2 (%): 16.8 (current)
Diloution: >6.0% / 18.2%

Last edited by rad-man; 03-05-2002 at 10:12 PM.
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Old 03-05-2002, 10:50 PM
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your mixture is too rich. I had similar readings - changed the O2 sensor (which was dead), and everything was back to normal. Your fuel consumption must be pretty high - get it fixed soon, otherwise you'll ruin the cats.
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Old 03-05-2002, 11:43 PM
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I was pretty sure it was a bad O2 sensor...

I just need to know which one to change. So it's going to cost me $65 just to get it scanned? Is there a cheaper way to find out?

I just checked, and there is a different part # for the sensor located before cat ($120), and a different part # for the one after ($160).

Are these resonable prices? Anyone recommend a cheaper place?

Last edited by rad-man; 03-05-2002 at 11:54 PM.
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Old 03-06-2002, 03:14 AM
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I've not dealt with them yet, so I'm not recommending them positively or negatively, but you can check:

also of course check fastlane above
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Old 03-06-2002, 08:24 AM
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O2 sensor should not go bad in40K miles, so there may be some other problem as well. Logically, it should be the precat sensor, since that's the one that controls the fuel mixture. But I would spend the $65 diagnostic charge to make sure something else is not at fault - I know, its not fair, but what do you do!
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Old 03-06-2002, 08:52 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
For those with instant cognition from scan data (no one I know), it takes more than four minutes. It takes an average of 15 minutes just to write the ticket and collect the money. Most of the time there is atleast another 15 minutes to discuss the findings. Of course all those involved with this work for free as you do of course.

After getting the car from the parking lot if I did you the favor and didn't road test it I probably could get the computer up and read your codes in a single module in 4 minutes but you have at least three modules that can be involved with the check engine light on a C220: DM diagnostic module (turned the light on), HFM runs the fuel and ignition, and the CC/ISC which may be in the HFM module on a C220 but is separate on most others (cruise control/idle speed control). If I wanted to fix your car pulling the codes would be the first in a long list of things I would do with the scanner, none of which would give me a final diagnosis if I am buying the parts. The tools I use to diagnose a check engine light cost over $100k. I will read codes and reset for one half hour labor. The only time I do this is for other shops that have turned a light on during other work and there isn't a real problem. I don't do that for the public because I can't write tickets for a half hour labor and have to deal with a customer also.

We believe that it costs us an hour of labor for all the accounting, coddling, government paperwork, and telephone time it takes for each ticket. If we ever charge less than 65 (our hourly rate) for a ticket someone worked for free. We do lots of work for no ticket or just for the part; wipers, bulbs, etc. for regular customers. We won't do it often for someone who obviously will not have us do the work that pays the bills.

I stay backed up with people that are more than willing to pay me to fix their car, many of them have already been everywhere else. I would have very little incentive to work on someones car who has any thought I may be ripping them off. Think about it!
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Last edited by stevebfl; 03-06-2002 at 08:59 AM.
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Old 03-06-2002, 09:33 AM
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ok, ok... I guess I'll pay the $65!
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Old 03-06-2002, 09:36 AM
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Imagine going to a neuro-surgeon and saying "you want how much for the diagnosis????"
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Old 03-06-2002, 09:53 AM
Registered User
Join Date: Apr 2000
Location: Indianapolis
Posts: 109
Fault codes notwithstanding, was the engine (cat) really nice and hot? Do some freeway blasts and keep the RPMs up in the parking lot to keep the cat hot - I agree that 40K is too short to replace O2.

My $0.02.

no emissions testing in IN
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Old 03-06-2002, 10:36 AM
Join Date: Feb 2000
Location: seattle, wa
Posts: 87

i agree with steve. $65 is a very reasonable rate to get a scan.maybe if you were a regular customer and you were going to have them do the work it may be cheaper. x-rays take 4 min too, but the expensive equipment has to be paid for.Remember, if consumers keep bringing their own parts to the local garage and want services for free,soon there won't be any garage to go to....jmo..Paul
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Old 03-06-2002, 10:47 AM
Posts: n/a
Yea, I was gunning it on the freeway to empty out the cats/warm them up before I went in for the inspection.
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