I need help. I have a 2001 230 SLK which I just purchased a couple months ago. The check engine light came on - the code said oxygen sensor, the front one. I have been reading on your posts that I should clean the MAF. I was wondering if I cleaned that if it would keep me from changing the sensor?? Also, I am pretty handy when it comes to cars, I change brakes, water pumps, alternators,plugs, wires, coils, sensors (some), radiators, belts etc. Most of the basic stuff. I downloaded the manual that was here on the posts but I'll tell ya, I don't have a clue where this MAF is located. Can someone enlighten me with specifics??

I don't know how much the Oxygen sensor costs, is there a certain place I should purchase it at?

Also, this car sits so close to the ground - stupid question---would it not hit the front if you drove it up on some ramps?

I haven't done anything to this car yet except change the plugs. It has just turned 100K on it so I would like to change all the fluids.

Any suggestions or instructions you can give would be greatly appreciated. I just love my car!! and want to keep it for a while.

Thanks
Penny

 

Hi Penny.

Yes you need to take care when driving onto ramp and especially when parking into a kerb (american style) etc.

Fuelling on your engine is controlled by a signal from the MAF which is located in the air inlet system. (If you search the forum you will find plenty of pics etc where this is located especially under Bazzle who has posted a nice DIY guide)

A signal from the MAF tells the injectors how much fuel to spray into the engine and the results are measured by the O2 sensor. Dependent upon the O2 signal and the MAF signal (both taken many times a second) fuelling is refined to the optimum level.

If you have a code which specifically states that the O2 sensor is wrong this points to a faulty O2 sensor. Its possible to access the actual output voltage and waveform of the O2 sensor if you have an appropriate scanner tool and these results will confirm if it is the O2 sensor at fault.

So the key here is what code is showing.

MAF problems are usually signalled by P0170/3.

I suggest only using only OE O2 and MAF sensors since assorted aftermarket (non OE) senors can give all sorts of strange problems. IMHO a large percentage of O2 sensors are changed unnecessarily. Sometimes changing them appears to overcome a problem BUT the underlying problem remains and after a short period of time the problem returns and necessitates other components to be changed. If however these other components were changed in the first place the O2 sensor would not have needed changing. the fuelling system has many input signals and any/many of these impact the O2 signal. e,g, Ambient temp and pressure, boost pressure, engine temp, engine speed, gear, etc etc

Hope this helps.

Stuart

 

Hi Stuart,

Thanks for the advice. I don't remember the code but I will go back and get it again. Can I get the CRC MAF cleaner at a regular auto store?Also,once I clean this MAF sensor, I am assuming I would need to reset my check engine light to see if that fixes my problem. I am guessing if it really is the O2 sensor thenthe light would come on again. I do not havetheappropriate scanner tool that you are speaking of I don't think, all I haveis adigital multimeter.

Also the ramp I was referring to was a ramp to work underneath the car - i think they are car or truck ramps. I still don't know if I would be able to drive up them.My neighbor down the street has a hydraulic lift in his garage. WOW!! I would love to have that!!!!! I have been thinking I need to make friends with him!! tee hee!!

Another thing - I read about changing my transmission fluid that you have to purchase a dip stick. Bazzel has a link on ebay to dipsticks but there are many to choose from. Is there a certain one I need to be looking at? I have many questions but I will search the posts for them.

Thanks so much for your input,
Penny

 

In the united states most parts houses sell Bosch O2 sensors, I know O'reilleys does..I would never use anything else.
http://www.boschautoparts.com/Products/OxygenSensors

Other componets failing can trigger 02 code as sensor is trying to compensate.
Heres a good OBDII site with some good info.
http://www.obdii.com/

My 1998 SLK front spoiler hits ramps when I use them. I assume yourramps arethe same popular type sold at most parts stores, wally worlds, etc. in the U.S.A. I am sure the degree of angle is the same on all these ramps. Use a peice of woodin front of ramps as pre-ramp. I cut angles into both endsof wood. I will give you dimensions of mine if ya need it, not too hard to figure out length, height,etc.the peice will look like this.ramp end-> \--\ <--end ya drive on. horrible illustration. Holler if ya need picture.

Bazzle has a post showing how to make trans. dipstick "tool" those dipstick measurements are dead on. I wish I had link to that post. buy a generic, universal dipstick or use curtian rod and make measurements. I have a dealership allergy and not gonna give them 60 bucks for that supposed "tool".

One other thing that will make some scream, is that if you have a component failure which caused vehicle to run rich contaminatingO2's, Iwill clean02 sensors with same cleaner used for MAF if I know they were good O2's..

These are my opinions and experiences only.. Good luck
Dumokie

 

Hi Penny.
Dependent upon codes MAF cleaner MAY work. This is not always the case dependent upon whether the MAF is out of range due to contamination or other reasons.
Dependent upon codes the Check Engine Light may go off on its own accord (if the fault that was sensed clears itself or by replacing a part). This requires the engine to be cycled (i.e. journeys) a few times. The CEL will not always clear itself.
Best to get codes read again and at the same time get the memory reset. This service is I understand FREE at many outlets in the USA. Even if the light comes on again you will have a better understanding of the fault since if the CEL comes on again the fault must still be present. Sometimes the CEL only comes on because some relatively extreme condition was experienced. i.e. Full throttle on cold engine or similar and if this condition is avoided the problem may notreappear.

Do noy fit "general purpose" O2 sensor. i.e. Fits all cars or ones where the wiring needs to be modified. Bosch area good make and SHOULD be compatible subject to previous sentence BUT I still prefer to use the genuine MB part even if that is made by Bosch. Small differences can exist that lead to strange problems. However many people don't experience these problems so act as you wish.

Good luck,

Stuart.

 

Oophs. Nearly forgot.

No need to change trans oil unless your vehicle has done well over 100k miles. Intended to be "sealed for life" although life is not defined and that is one of the reasons why there is no dipstick. Correct oil level in the trans is very important. Oil temp control and flat ground are MUSTS when checking.

IF you really do want to change the oil it is VITAL that you use GENUINE MB TRANS oil (very expensive vs normal Dextron etc) otherwise changing the oil will make matters WORSE rather than BETTER. BE WARNED.

If you do change the oil ensure that there is no leak from the electrical connection adaptor and while yoy are at it change the filter within the trans. I changed mine because I had a slight oil leak but there was no debris in the sump pan at all and even after 120k miles the oil appeared clean, the correct colour (red) and didn't smell untoward.

If there is debris in the sump begin to prepare yourself for the worse!

Do not overtighten the sump bolts in order to correct an apparent oil leak from the sump gasket. Toghtening the bolts doesn't pull the gasket down tighter and in any case the leak is usually from the electrical connector rather than the sump pan although several individuals have challenged this until finally they accept that it is the electrical connector.

Stuart.

 

Okay Dumokie and Stuart, I cleaned the MAF sensor and went and had my check engine light reset so we will see if it comes back on. I had them read the codes again and they were P0135 -heater circuit malfunction; P0132 O2 high voltage bank 1; P0130 O2 circuit mailfunction; P0131 O2 low voltage bank 1; P0171 system too lean. So we will see. I am hoping the cleaning fixed these things.

Stuart, I do have over 100,000 miles, 103 to be exact and I feel I should change the transmission fluid and brake fluid. In your explaination of the ramps -- I am trying to envision this and I can see a ramp in front of a ramp basically, if you don't mind - shoot me your measurements. I can build it. Also when you have the front up on the ramp do you lift the back and put jack stands under the back? I would think it would make it easier to get to.

Also Dumokie, you mentioned about cleaning your O2 sensor - I take it you just remove it and spray it with the sensor cleaner - how hard is it to remove? Do I have to be real careful not to damage anything??

Thanks for your help,
Penny

 

[:@] Okay, my check engine light came back on so, I am going to take the sensor out tomorrow and clean it but I am not very hopeful- it sounds like I will have to replace it. Do those codes mean anything to you?? Could it be something else?

Like a coil or something?

Penny

 

Okie Dokie here we go.. Wonder, first want to give you this link to great SLK site, be sure and check it out. Think you will be using it alot!
http://www.buellwinkle.com/r170/
So we have PO135,132,130,131,171 initially as codes. Would love to see what new codes are, after MAF clean, think that willbe critical.
Anyway wehave alot of 02 codes so lets address that first...
The 02 sensor element is aceramic cylinder plated inside and out with porousplatinum electrodes, It is also know as a lambda probe, the whole assembly is protected by a metal gauze. It operates by measuring the difference in oxygen between the exhaust gas and the external air, and generates a voltage depending on the difference between the two. The sensors only work effectively when heated to approximately 300°C, so most newer 02 sensor probes have heating elements encased in the ceramic to bring the ceramic tip up to temperature quickly when the exhaust is cold. The probe typically has four wires attached to it,, two for thevoltage output, and two for the heater power, although some automakers use a common ground for the sensor element and heaters, resulting in three wires. Earlier non-electrically-heater sensors had one or two wires.
So there we see that the 02 creates electricity depending on the fuel mixture passing through it in exhaust. Less fuel (lean) will give you a lower signal about 0.2 V with more fuel or a (rich) mixture being about 0.8 V. Ideal is about 0.45..
Remember seeing that most 02'sare heated as yours are? well that is the PO135 code, but that does not mean that failure is actually in the02 sensor heatingelement (usually is) but it could be wiring going to the sensor, bad connection where 02 plugs in, remember that a "circuit malfuntion", includes whole circuit. I feel that is possibly is a real legit code that can be addressed later.
Codes PO132 and PO131 kinda conflict and point to the fuel mixture going crazy.. one code saying too much fuel and another saying not enough fuel... This means the 02 has steadily given the ECU (computer) a steady high or low voltage.O2 sensor is working and telling you that something else is causing mixture screw up and trying to compensate.
Heres good 02 site, lots are out there.
http://www.mr2.com/TEXT/O2_Sensor.html

Here is a breakdown of a02 sensor
http://www.autozone.com/az/cds/en_us...rInfoPages.htm

Then you have the PO130 code which is saying the02 sensor is not any good. Very well could be. Because this sensor been working its *** off trying to send signal to computer that the fuel mixture is crazy.

What we are shooting for is if the engine burns too lean, the sensor will detect the mixture as being too lean (low voltage), and the engine computer will adjust the injector pulse duration (injector pulse width is how long injector stays open and sprays fuel into engine), and give more fuel. If it detects rich(high voltage) then less fuel so that the air-fuel mixture continues to stay within the stoichiometric ratio of 14.7:1 on a typical vehicle. Stoichio is considered the perfect mixture to burn allfuel and give maximum umph.
Normally, the lifetime of the sensor is about 30,000 to 50,000 miles. The failure is usually caused by buildup of a deposit on the probe, this canNOT normallybe cleaned off to answer your question. When I clean them is when I know its a good, low mileage sensor which has been contaiminated due to a rich running condition.An overly rich mixture causes buildup of black powdery deposit on the probe. Similiar to a fouled spark plug. So going back to autozone sensor breakdown you would spray through #7 to clean #9 and 10..If new O2 gets contaiminated itis a problem elsewhere in the fuel rationing system.
If you go to O'reillys and get a Bosch 02 sensor then compare part number to the one from dealer they will be the same, but there will be a HUGE price difference!!
If, I were you I would cruise by parts house and have them show you a 02 sensor so you familiarize yourself with it. Have them show you the special socket you need to remove and install sensor. Below is link to some sockets. Remember 02 haswires coming out of top so socket allows for this. but other than that its as simple as changing a spark plug.
http://www.justoffbase.co.uk/Tool-Sh...Sensor-Sockets
http://thetoolnetwork.com/schley_sp_...or_socket_.htm
If you ask me, your vehicle has other issues, but we need to start with the basics and work from there. I don't think its a ignition problem, if coil is bad you will have a miss, stumble, bad idle.. I don't think you ever said how car actually runs (performs), how does it idle?
SO BACK TO BASICS,AIR FILTER, FUEL FILTER... CAN YOU GET ANY INFO FROM PREVIOUS OWNER? WHAT HAS BEEN DONE TO CAR? Fuel filter been replaced lately?? You have good fuel pressure? Locate 02 wiring and look for burnt wiring, bad connections,etc.. Try to start figuring out where other sensors are such as the T.P.S. throttle position sensor, M.A.F.,and others, check their connectors...Use component locator on the site I gave you, I think you are gonna find it invaluable.

Lets get it running good and C.E.L. (check engine light) off before other issues such as tranny service. Everyone has their own opinion, there was a thread about 30 pages long on one M.B. site bantering back and forth ad naseum. I rebuild ZF transmissions which is what you have, and service mine regularly.
Some say that service causes failure, but when youdig you find that service was performed to try to correct a transmission driveablility issue which waswhat was actually was wrong, or transmission was on verge of failure.. There is no such thing as a life time sealed tranmission, thats bull****.What that means is they don't want you to service your so it will go out regurlarly in your lifetime. The dealer performs service on these transmissions, Dealer sells filters and pan gaskets. So whats up with that???? Anywhere you have alot of heat and friction theres gonna be wear/tear and thats what transmissions do. I use ATF+4 fluid in mine which is what Chrysler uses.. Guess who's transmission Chrysler is using?? Zahnradfabrik (ZF).. The ATF+4 works in the same transmission in a different car (chrysler) but you have to buy a insanely overpriced fluid for same trans. in a mercedes?? So now we opened that bag of wormstry not to get sidetracked on that now. lets get your car running well. Don't get me started on the dealers!
Make sure basics are good, get new codes, go ahead and familiarize with 02 replace as needed.. M.A.F. seems to be fine. Check wiring. Use these forums they are great and will save money and heartache..
Dumokie

 

Hi Penny,
Wow, what more would you like to know now Dumokie has done a (good) brain dump.

Firstly the ramp dimension thing was NOT from me.

WRT changing trans fluid I also sit on the fence here since I changed mine at 100k but did so primarily to address a leak and change the filter.
Sealed for life is the MB(UK) response, not mine. Prevention of potential ingress of contamination is a more important requirement than oil life.
However the oil used by MB IS somehow different to regular Dextron etc. I don't know why or what the difference is. It looks, smells and feels very different. Of corse it could be a clandestine plot to put people like us off the scent. May be made to look different just to justify the cost but I think not.

Unless the trans is used for heavy duty towing / ambient temp / ultra high speed then the oil will not have degraded at 100k and the filter will remove any debris the majority of which SHOULD BE manufacturing debris and band "sludge". If there is debris other than manufacturing swarf etc then the trans is on its way out anyway so an oil change is only likely to effect a temporary improvement at best.

If the trans has done less than 100k changing the oil is pointless. At 100k then OK but use of oil other than the MB oil MAY introduce new and unwanted issues and CLEANLINESS IS VITAL. The choice is yours.
Maybe Dumokie can provide some data on the difference in the oil. SAE spec vs SAE/MB spec etc. since it appears he repair trans for as living.

The same sort of issue arises over engine oil change points.
In the USA you appear to change oil very frequently (presumably so it looks nice and clean) whereas in Europe and in particular Germany (which is one of the only places in the world where you can drive at speeds anything like the car is capable of) oil change points have been extended by the use of special synthethic oils which work better under extreme conditions vs regular oil.
As I understand it MB have recently been on the wrong end of a class action for millions because the wrong oil/sevice change points have been used in the USA as a consequence of local custom and practice. Vehicles have been refilled using regular mineral oils vs "special" synthethic and damage has resulted. Owners have thought they were being responsible getting their oil changed but the local servicxe stations haven't used the correct recommended oil.
The recommended MB Mobil 1 0w-40 oil costs in the region of 100-150USD peroil change in the UK although I believe it is a fraction of this in the USA.

My advice use the recommend oils (and parts) unless the exact same part is available at lower cost.

For instance many Bosch after market parts are NOT the same as Bosch OE supplied parts due to licencing agreements etc. The difference MAY only be that sometimes a MB part number (which is stamped in in addition to the Bosch number) and logo are on the component but the parts are likely different in other ways as well. i.e. Surface finish, material spec, performance spec even when made by the same manufacturing company.

However many non OE parts MAY perform adequately and meet most peoples needs under normal day to day conditions so the choice is once again down to the user.

Now the important bit.

Your codes all point to the O2 sensor BUT this does not mean that it is the sensor that is wrong.
Some of the codes are "startup" test faults and others running faults.
Unfortunately yours is a 230 vs 320 SLK so you cannot do a Bank1 to Bank 2 swap out.

Dumokie recommendation is correct in that you need to start from the beginning to ensure all the basics are correct and where possible try to establish some history. i.e. Has this problem recently appeared or was it present on the car when you got it or at least very shortly afterwards and may therefore have been the reason why thecar was sold.

My recommendation is to ensure the basics are correct and to then get the car hooked up to a scanner that is capable of reading real time data from the onboard sensors.

You will then be able to observe the O2 sensor output and to confirm whether the voltage is high, low, incorrect cycling etc before randomly changing the O2 sensor.

However the plethora of O2 sensor faults seems to point to the O2 sensor and it may be sensible to just fit a new one since even if this is not the cause you will have eliminated a key possibility.

Sure you fuel is OK?
Using oil which may have caused contamination.
Any work been done on the engine. Silicon sealant kills an O2 sensor at extremely small concentrations?
What does the tip of the O2 sensor look like (i.e. colour)
O2 sensor connections good? Any corrosion on multiway connectors?

O2 sensor change is straightforward so long as you use a good (single hex preferable) socket and ensure you keep the tool parallel with the axis of the sensor (sometimes difficult due to access) otherwise you may damage the porcelain insulation. The sensor may be VERY tight. Do not overtighten when refitting and use APPROPRIATE release agent. O2 sensors are very sensitive to contamination poisioning.

Ensure you have the car safely jacked and blocked before working under it!
Good luck.

Stuart