Hi all,

My car failed its inspection yesterday, due to 4 errors (all related). My check engine light has been on for a while, which I've been intending to get fixed as well.

The 4 errors were:
P0141 O2 Sensor B1 S2 Htr Malf
P0136 O2 Sensor B1 S2 Malf
P0171 Bank 1 System Too Lean
P0138 O2 Sensor B1 S2 High Volt

My car is generally driving ok, except sometimes when pushing the gas hard, it seems to lack responsiveness / power.

Anyhow. Last night I did quite an big search of this forum and via google. I found the DIY for replacing the MAF which I need to refer to at some point. I also found quite a suprising amount of information about 'cleaning' various parts, such as the connectors for the MAF, etc that may resolve the issue. It appears from others posts the really the O2 Sensors should not 'fail' that easily.

Now it may or may not be related (I think probably not since it was a while ago), but I did replace my air filter (stock) with a K&N one. I already had the check engine light on at this point, so I'm not convinced the filter is a cause. After I put in the K&N filter, I did not notice an difference in performance (wasnt really expecting to).

My question(s) are:

(1). Can i 'clean' the O2 Sensor B1 (Bank 1)? If so, where exactly is this sensor?
(2). Is it worth cleaning out the MAF too? I see several reports of buying a MAF spray for $6 or so.
(3). If I do successfully 'clean' these parts - how can I test it to see if it made any difference?

I've also read that I would need to drive the car for some odd 350 miles before the ECU is properly 'reset'. I am curious to know if doing the ECU reset posted on the DIY would have the same effect?

Am I even on the right track doing these things?

My car is a C230K Coupe, 6 speed manual, with just over 27,000 miles on the clock.

All suggestions greatly appreciated.

 

With a CEL you will fail automatically...

 

Your cam sensors are leaking oil into the engine harness, causing the MAF and O2 sensors to give bad readings, thus the CEL.

https://mbworld.org/forums/showthrea...=226338&page=1

Read this thread, it'll tell you exactly what to do.

 

Or it could be that your O2 sensor is dead, these things die guys. I fit high numbers of these things to various models on a weekly basis. Just because there is a common problem with the cam sensors leaking oil into the harness doesn't mean every O2 sensor problem is because of this.
Just thought you should know before you go ahead doing work that doesn't need doing.

 

Thanks - I'm hoping (!) that I get a few responses so I can see what overall opinion is.

I'm still not clear where this O2 Sensor even is (bank 1). I'm happy to at least attempt to fix it, bit could use some inital direction!

Amoanonfire - thanks too. I'll hold off a bit before doing all this work

Capt_Paul - Fail automatically, how? As in the person will fail it, or connecting it to the machine flag the CEL and fail it. The person who ran the test said 'it might fail based on that (CEL)' before he hooked it up.

 

All those codes seem to point to the o2 sensor, bank one is the pre-cat o2 sensor, you can't really clean the sensor, but you should spray the MAF.

These sensors build up carbon and it kills them after a while. They need to be replaced.

The running lean code is probably due to the sensor not working.

 

Just check the cam sensor connector for oil, it takes 2 mins, most of which is opening and closing the hood.

Don't "hope" that someone here will solve it, you need to diagnose it. Check the cam sensors for leaks, plug in an OBD monitor and see if the O2 sensors are outputting voltages in the correct range, same with the MAF, get a vacuum leak check done, ...

The cam sensor leak causes the engine to run too rich, not lean, so I suspect its not this problem, especially since you only have 27K miles, yet it doesn't hurt to eliminate it from the list of possibilities and only takes 2 mins to check!

 

Dachigga,

Where is this sensor exactly? I've yet to see any images / description of the location!

Help!

(and thanks)

I agree about the lean code, and actually the guy doing the inspection said the same too.

 

Amanonfire - thanks. I certainly don't assume that someone will solve it, I'm just wanting to eliminate all the obvious / simple things first (that I can do myself) before taking it to MB.

I'll check the cam sensors tonight - I just checked the other links you gave earlier, they have pics of the cam sensor links...(still looking for the O2 Sensor - bank 1 though)...

 

I had exactly the same error codes on my 2002 C230 (I have 2.3 and you have 1.8) and I replaced both sensors and it cured all of the faults. I don't think that your mileage is enough to warrant o2 sensor replacement but the car is 5 years old regardless of miles so that might be it. I replaced my sensors with universal ones from Autozone and they worked fine. It's just a sensor so no need to buy oem. It was over a year ago so I don't remember exactly where they were but I seem to remember one on the manifold (up high in engine bay) and the other under the car before the shifter.

Hope this helps!

 

On the M271 (your engine) the O2 sensors are both visible from the engine bay. Look on the passenger side of the engine, at the exhaust manifold, you should see a long sensor sticking out of it at the top, and another much further down, almost at the bottom, and a giant metal cylinder in the middle. The metal cylinder is the primary cat, the top sensor is the pre-cat sensor, the bottom sensor is the secondary sensor.

The secondary sensor is rarely the problem unless the cat is done, which in your case is unlikely. Its most likely the pre-cat since its the one that takes the most abuse prior to the cat filtering out particles.

The M271 only has 1 bank, its an inline 4, not a V6/V8/V12/...

Any garage should beable to help you, this is not a problem specific to MB.
The O2 sensors are ~$100 each online, yet it gets expensive buying parts and replacing, only not to fix the problem.

 

I would say with great certainty that the 02 sensor have not failed at 25K miles, and it is much more likely you have oil in the wires as suggested.
02 sensors last at LEAST 100K miles without failure under normal circumstances.

 

Update - I checked both Cam Sensors, the left one did appear to have some black fluid in it, which I assume was oil. I cleaned it out properly and checked over the MAF connectors too.

I didnt have a chance/time to locate the O2 sensors (still wouldnt mind some pics!), thats my next check.

I started the car up and it spluttered for a slight second then resumed idling at a normal rate. I'll take it for a spin tomorrow and see what happens. I was thinking it might be worth resetting the ECU as shown in the DIY section before driving it tomorrow?

Thanks all for the help so far.

 

The O2 sensor connectors are under the car, you have to jack up the car and remove an underbody panel (furthest rear panel under the engine) to access them. Checking the sensors on the manifold won't tell you anything.

Check the ECU and MAF connectors, most likely they have a thin film of oil in them (unnoticeable to most, I overlooked it at first too).

If there is oil in the cam connector, then you have to:
- change cam sensors
- install isolation cables
- clean all affected connectors (MAF, ECU, O2, TB, knock sensor, crank sensor, ...)
- hope nothing is damaged (most likely not)

Do this soon, prolonged oil leakage has caused damaged several ECUs.

 

Brit,
You still around? What was the resolution?
I have a P0171 error I need to clear up.

 

Just a heads up. I just recieved a p0036 code, bank 2-sensor 2 code. Rockauto.com had the Bosch oem sensor for $53 shipped!

Dealer wanted $210, autozone $170, amazon $115.

It pays to hunt around.

 

Sport Coup, I just had a P0171 code that I just erased, also had P0600 which I highly suspect is my HVAC unit but I'm not worried about that one since it works most of the time.

I am getting a slight shudder at low engine speeds/idle, it gets worse when the AC is on (more load). I'm suspecting a dirty MAF. The $12 hose campaign has been performed on the car already and I'm at 122k miles. When I get a couple of days I will clean the MAF out and go from there. I will also post on here to update everyone.

 

^ what is this $12 hose campaign you speak of?

 

Effects M271 1.8L 4 bangers,