I have a 1999 SL500 that the check engine light came on a few days ago. I had it checked and reset. But the check engine light comes back after about 50 miles. I was told that its needs to be brought in to a mercedes dealer to be repaired. The code has been for a mass air, 0173 left adapt at limit and now for PO170 & PO 173 fuel trim.
I looked into it and they want large dollars for the air filters, fuel filter and mass air.I can save quite alot by putting them in myself if I can find an instruction manual. Is there somewhere I can find out how to install thes parts. Also , has anyone had this problem and how did you solve it?
Thanks

 

Roadman,
IMO, these codes all point to the same root cause....dirty MAF Sensor in the intake. Ideas about changing air filters is correct as these filters (2) clean the air prior to hitting the MAF. If the filters are 'full', dirt gets past and settles on the MAF sensor. You can order the filters from www.autohausaz.com ; get the OEM paper filters.

To install, remove both sections of the engine cover; set the front portion aside. Turn the rear section over, and you'll see two covered compartments held down by 6 or 8 TorX screws, T-20's I believe. Remove the covers, take out the old filters, wipe the inside of the chambers clean, install the new ones in reverse order.

For the MAF Sensor....get a can of CRC MAF Sensor spray cleaner at Autozone, PepBoys, etc. Follow the instructions on the can to spray the sensor. Once you have the covers off you'll see the round housing on the top of the manifold that holds the sensor. You should, with a T-20 Tamper Resistant driver, remove the sensor from the housing before you start spraying it. You should examine the sensor wire to make sure it's not broken. If it is, you'll have to replace it; part number is stamped on the sensor. You can get all the tools and spray at AutoZone.

I wouldn't do the fuel filter myself as it's in a non-friendly location under the gas tank by the fuel pump. Much easier to work on if the car is on a lift, so I had my indy mechanic change it.

Have fun-

Bob

Almost forgot...when you reinstall the sensor plug, and put the engine cover back on and start the car, your ECU(computer) will now be getting fresh data from the sensor and make the run corrections to fuel trim, etc, by itself. The engine will adapt to the new settings and after running rough for a few minutes, will suddenly run like a new one. Just drive it for 15 minutes or so and you'll be fine. If the CEL light doesn't go out by itself, Autozone can turn it off for you.

 

I've never worked on this car and I don't want to break the engine cover. How is the engine cover removed?
I went to the website and checked the filters should I get the Bosch or the other one? Same question with the fuel filter?
If it turns out the wire on the MAS is broken, should I get that at Autohaus or would they have that at Auto Zone?
To remove the Torx screws you use the T20, is that the same driver as the T20 tamper resistant driver?
Thanks

 

Hengst/Mann or Bosch, both are German and good. the first/front cover should pull up then un-snap out. Air filter housing pulls up from front then rear and pulls up and out. MAF wires broken is 1 in 10000. But check anyway.

 

Here's the results
I cleaned theMAS and the air filters this morning. The wires in theMAS were intacked. The air filters were just a little dirty so I blew them out with compressor. I'll order some new ones.
After putting it back together, I took it out and within 3 miles the CEL came on just as I was told it would. I drove it about 40 more miles. It did seemquicker. I went at varying speeds up to 100. Most in the 50 -75 range.
I then took it and had the code checked and it was the P0173 fuel trim again.
It was then reset and I drove 70 more miles. No codes have come back on yet.
The only problem I'm seeing is that it feels like its running rough at idle.
Barely noticeable when the car is in drive, rpms are at about a little over 500.
When the car is in park and idling, its very noticeable. RPM's go up to maybe 600+ but hard to tell exactly.
This was happening before I cleaned the MAS, so could this be related?
I called a couple mercedes dealers service to see if I could get any info but they just want you to bring it in for a diagnosis..
The only thing that was mentioned was it possibly could be an oygen or knock sensor..
My questions are these:
Do you think having driven 70 miles after the code was reset, is that problem resolved? I know it takes the computor awhile to recalibrate.
What could be causing the idle problem?
Thanks for ny help in advance.

 

It just dawned on me that possibly there could be a vacuum hose loose or disconnected. I looked and don't see one, but is there one that would make the idle rough?

 

PM Sent in Reply to yours...

Bob

 

John, in your other message, you said...

The only problem I'm seeing is that it feels like its running rough at idle.
Barely noticeable when the car is in drive, rpms are at about a little over 500.
When the car is in park and idling, its very noticeable. RPM's go up to maybe 600+ but hard to tell exactly.

If you are feeling a vibration seeming to come through the seat, this is what you should do to diagnose the problem....

With the hood raised and engine running, put your left foot FIRMLY on the brake.

Put the transselector in D; engine RPM should be around 500-600

While watching the engine through the opening at the base of the hood, and keeping your left foot on the brake, quickly'goose' the accelerator up to about 1500 RPM and let off the accelerator. Punch the accelerator several times and note what the engine does as you do.

I suspect you'll either see one side of the engine appear to lift upward, or the engine will appear to rock front to back.

If this is in fact what happens when you punch the accelerator as indicated, either 1 motor mount or possibly both have failed or are failing. The vibration you're feeling through the seat is from the engine literally vibrating on the frame and the car's harmonics let you feel it via the seat.

Even if only 1 mount has failed, you'll need to replace both sides. And, as long as you're in there, to minimize near future labor costs, I would also change the transmission mounts at the same time. Your tech can advise you on this. By the way, this is not Dealer only work; if you use a GOOD MB independent, this is a straight forward repair.

One last question, MB issued a recall campaign for the harmonic balancers situated at the end of the crankshaft (bottom center pulley that your serpentine belt goes around) MB apparently got a load of defective balancers, and since they act as a counterweight to the crankshaft, if yours was never changed via the recall, there is an outside possibility that this balancer could also contribute to the vibration you feel.

If you don't know if this was ever done, call the MB Dealer on Monday and give them your VIN #; they can pull up via VMI whether your car is a candidate for the free replacement and/or if it was ever done at all.

That's all I got, bud, I'm done for the night.

Bob

 

Bob, thanks for all the replies and work your doing in regards to this problem.
I did as you said with the vibration. When I goosedthe engine, itlifted r to l and then the next time it went r to l. It didn't lift front to back or back to front. After each time when the rpm's dropped back down, I heard 2 clicks.
I'm assuming that its the mounts, any idea what the 2 clicks would be.
Any ballpark numbers onwhat it costs to do the mounts?
Can you give me idea what they have to do to replace the mounts, do they have to pull the engine?

I didn't drive it but the CEL didn't stay on when I started it.
John

 

Well John, your welcome!

The side to side movement is indicative of failed mount(s). At 50K miles +/- this is an expected maintenance item. In estimating the cost, your independent MB Tech is of course the best source (I'm assuming you have one) and don't fully depend on the Dealer for maintenance service. That said, the engine mounts for OE (Boge) will run around $100-$125@ if ordered by your independent tech, or around $175@ if from the dealer. The transmission mounts, either Corteco or MTC/Meyle, will run about $30@, ordered by your tech. Labor to install both should be around 3-6 hours at whatever your local labor rate is. You'd be wise to get an estimate on a job like this. And NO, the engine does not have to come out.

I'm suggesting you do both pairs of mounts since at least 1 engine mount is bad, part of the weight of the engine is now being transferred to the frame and transmission mounts, thereby weakening them. As I said earlier, as long as the tech has gone this deep into the job for the motor mounts, you might as well do the trans.

As far as the clicks you heard, I'd only be guessing that the sound is coming from either of the mounts, engine or trans. Either that or your Driver Adaptive Transmission is saying, 'what the hell are you doing?'

Speaking of the trans, if you've got 50K on it, you may want to consider flush/filter/refill of the transmission. I realize I'm spending your money for you, but if like me, you don't buy the MB claim of 'filled for life' transmission fluid, I'd get it done. Our model year still had the drain plug on the torque convertor....MAKE SURE your tech doesn't get lazy and skip draining this component...it's important.

Last, you didn't mention anything about the harmonic balancer recall/replacement I referenced in another post. I looked up the affected 129 models and if the last 7 digits of your VIN# falls in the range from ...F169044 to .....F196751, your car is elegible for this free replacement. Your dealer can confirm, however, your indy can do the replacement work and MB will reimburse you for your out-of-pocket expense via their published Recall/Campaign Service Bulletin.

Good luck with this, and since the codes didn't come back on, I think you nailed the source simply by cleaning the MAF Sensor. Good Job!

I'm off to the beach, have a great day!

Bob