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Old 05-16-2003, 06:36 PM
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Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
O2 sensors

O2 sensors should be replaced every now and then since they have a big grey area, as in, at first they work very well, then they enter the grey area where they still work but don't give the perfect readings, and most of the time they stay in that area before they die completely at which point you will probably go bankrupt from gas bills, and change everything else in the car except the O2 in order to fix a stalling, or rough idle problem.

There is a way to clean an O2 sensor, since it is in the exhaust, the only wear and tear it is subjec to is temperature, which it is immune to for the most part, and carbon deposits which cover it bit by bit until it's too covered up to work.

You can clean it in the same manner you clean a muffler for a motorcycle, you simply take a blow torch and burn all the carbon deposits to a crips, in most cases they will catch of fire, then you scrub off the ash with a brush and it's good as new, the only problem is that in order to set the carbon deposits on fire, you have to heat up the poor O2 to a very high temp, at which point you more or less will destroy it unless you have some kind of practice, but how you get this practice I have no clue. And this is why you should replace an O2 instead of cleaning it.

1985 190E 2.3L - a constant project.
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Old 05-16-2003, 06:37 PM
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Join Date: Sep 2002
Posts: 2,485
Given the cost of O2 sensors, I wouldn't recommend replacing them unless they fail. On OBD equipped vehicles, the "CHECK ENGINE" light will come on before the faulty sensor causes driveability problems. Also, keep in mind that O2 sensors can fail in several ways. Arthur Dalton is right on the money when it comes to the PO411 logic chain. When the AIR pump is switched on the O2 sensor voltage should drop below 40 mV almost immediately. As sensors age they may not react quickly enough or completely enough to satisfy the OBD test criteria. This sets a trouble code but the O2 sensor still functions well enough to ensure good engine performance. The EGR test criteria uses manifold pressure(vacuum)to determine whether or not the EGR system is working normally or not. A slight vacuum leak can cause EGR codes even though the system is working. "CHECK ENGINE" lights are really very simple to correctly diagnose as long as you know the parameters/ test criteria of the particular trouble code you're trying eliminate.
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Old 05-18-2003, 02:16 AM
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Join Date: Oct 2001
Posts: 226
I think I found the problem. The plastic tubing connecting between the EGR valve and, I believe, the air pump was cracked in half under the plastic engine cover. The entire tubing was hard and brittle. For now, I had some rubber hose to reconnect the plastic tubing. I will probably replace the entire tubing when I get the chance.
I noticed that on the plastice tubing right next to the one I fixed that this type of rubber connection "fix" had been previously done. This must have been the dealer mechanics who had checked and fixed a previous CE light condition a couple of years ago. At that time they said they replaced the rubber connector and charged me over $100 bucks for the fix. I have ABSOLUTELY no problem paying them for their knowledge and skill for the fix, however, I'm a little peeved that they did not actually replace the plastic tubing that was actually the problem and would obviously crack in other places later instead of connecting the broken pieces together. Kind of half ass. That tubing and the tubing I fixed temporarily was VERY brittle (broke it a couple times trying to remove it) and obviously is affected by heat and time. Sorry, I'm done venting, moving on.

If this was the problem, will the CE light eventually go out by itself? I've read a post where someone said after a certain number of "drive cycles" without the error the CE light goes out. If true, what is a "drive cycle"? I wonder, because most of my trips are short and would they qualify to the computer as a "drive cycle"? I know I can disconnect the battery, but it would kind of nice if the car realizes by itself that the problem was corrected (affirmative confirmation).
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Old 05-18-2003, 11:12 AM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,784
'93 W124, 3.2 liter M104 - CE light, found 2 codes
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Old 05-19-2003, 01:10 PM
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Join Date: Oct 2001
Posts: 226
Thanks, Arthur. That looks like that pretty much covers the problem.

Again, does the CE light eventually go out by itself? If so, what are the parameters for the clearing process? I know the code will remain until it is cleared with a scanner.
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Old 05-19-2003, 01:52 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,784
Not many options w/obd2
Battery disconnect [ don't forget radio code- ]
Scanner clearing
Auto reset..

the OBD1 systems are nice for DIYers BC you can make a $5 tool [ and some even have the tool built-in under the hood], but those days are gone...
There again, OBD2 has so much more info..
I guess a Computer interface and/or scanner may not be a bad idea for those inclined..
They tell me Auto-Zoney does it for free..

A PS on your plastic vac line , et al..
This line is a Common [ shared] vac source feed to both the EGR AND AIR SOVs, so you can see where you can get double problems with a cracked one..[ and they ALL crack..I replace the entire line w/good rubber one]
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Old 05-23-2003, 01:48 PM
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Join Date: Oct 2001
Posts: 226
Any idea how long it takes to auto reset?
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