CEL, running rich - help. - Mercedes-Benz Forum
 
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#1 (permalink) Old 12-05-2008, 12:19 PM
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CEL, running rich - help.

Ok yesterday I see a check engine. So this morning I plug in the reader and get back PO172, Running Rich bank 1.

The car is at about 49000, C230K 04, out of warranty. About 500 miles back I noticed the cam sensor connectors were slightly oily so I replaced the sensors and have the extended harness in place.
I didnt check the MAF sensor at the time. The only change recently is I went to Chevron while the tanker was refilling but I usually only got to Shell, dont think that matters though.

Can anyone provide some insight as to what I should check / replace, O2 sensor? plugs?
My first thought was crap I have the change the engine harness from the cam sensor oil seapage, but hopefully not (crossing fingers).
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#2 (permalink) Old 12-05-2008, 12:59 PM
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I see that your replaced your cam sensors because they were leaking. They might have leaked onto your ME(Engine Control Module) or onto the MAF. You can use Electronic contact cleaner. Double check the harnesses, becuase these cars are famous for oil traveling up the wire. If the MAF has oil on it, its pretty much shot. You would need to clean out the INtercooler(charge pipes) and change the MAF. If you need futher help, let me know.
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#3 (permalink) Old 12-07-2008, 11:04 AM
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You can always reset the code, disconnect the MAF and run it for a while. If you don't get a P0172 code again then it's the MAF, a good cleaning will fix it. If you don't, then it's not the MAF. Obviously you'll get a MAF error but ignore that for now.

Where was the oil leaking from the cam magnet sensors (I assume it's not the cam position sensor)? If it's just some seepage around the perimeter, that's normal. If it's actually inside the connector, then you have work ahead of you. What happens is that the oil travels to the lowest point which are the O2 sensors and that can explain an error in determining the correct fuel mixture. Personally, I would replace the entire harness rather than risk having more components damaged.

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#4 (permalink) Old 12-08-2008, 12:18 PM
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Yeah when I replaced the sensors the connectors were slightly oily. So i realized I have the dreaded cam sensor magnet issue.

What I did was reset the code and drove around with the MAF disconnected, then the next day i reconnected the MAF and drove about 50 miles with no CEL.

So right now I am not sure what caused it? Possibly oil in the harness or O2 sensors. I think the job is beyond my skill set so I will most likely have to eventually take it in and find out how much its gonna hurt.
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#5 (permalink) Old 12-08-2008, 12:37 PM
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Originally Posted by richmds1 View Post
So right now I am not sure what caused it? Possibly oil in the harness or O2 sensors. I think the job is beyond my skill set so I will most likely have to eventually take it in and find out how much its gonna hurt.
If you can use a jack, a socket, and a spray can - you can DIY.

Your O2 sensor connectors are likely coated in oil.
- Jack up the drivers front side of the car
- Remove the belly pan under the engine
- Find the 2 O2 connectors (beside the oil drain plug)
- Disconnect and spray with electrical contact cleaner
- Repeat
- Repeat
- Repeat until no oil drips from the connector
- Attach connectors
- Replace belly pan
- Lower car
- Enjoy better gas mileage and no CELs

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#6 (permalink) Old 12-08-2008, 01:03 PM
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Thanks taylor192, I will check it out.
Funny, last time I did an oil change it was PITA to do the drain plug method. I was thinking I am going to do it suction way next time around.
Guess I will drain plug a while longer since I have to keep checking that O2 sensor for oil.
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#7 (permalink) Old 12-08-2008, 01:11 PM
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Originally Posted by richmds1 View Post
Thanks taylor192, I will check it out.
Funny, last time I did an oil change it was PITA to do the drain plug method. I was thinking I am going to do it suction way next time around.
Guess I will drain plug a while longer since I have to keep checking that O2 sensor for oil.
I just did the opposite, bought a hand-pump suction machine, and honestly I could've done it far faster via the drain plug. Sucking dirty oil up via the small tubes takes a long time.

If cleaning doesn't help, replace the O2 sensors. They are $80/each and take 10 mins to replace with a large adjustable wrench.

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