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1999 SL500 R129
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97 Posts
Discussion Starter #1
Hi, everyone! I'm having a weird issue with my '99 SL500. My CEL continues to come on, but my shop says there are no stored codes. In the last week, I've replaced the EGR valve and the shop has done a smoke test to make sure there are no vacuum leaks. The car runs great and I'm getting good mileage. In the past, it would come on every so often, then go off again after several starts. Last week, however, after the EGR valve replacement, the CEL came on and stayed on for a week. Friday, I went back to the shop for the smoke test and code check; nothing. They cleared the code. Then, last night, it reappeared...

Any theories?

Thanks!

Ben
 

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Departed 1998 SL500 (and the Pano is in Bogota)
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11,000 Posts
What shop are you using ?
Are they specialize in MB with the proper scanner for MB ? or just scanning with an OBD-II port scanner ?
 

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1999 SL500 R129
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97 Posts
Discussion Starter #6
Thanks for your input. They are a Mercedes and German specialist shop. The owner is a former Mercedes master tech and they have all the updated diagnostic tools. They do overflow warranty work for the local dealer...
 

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Departed 1998 SL500 (and the Pano is in Bogota)
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11,000 Posts
It is indeed a mystery if your MB specialist shop with the proper equipment can't find the code that caused the CEL. As your car seems to drive OK even with CEL ON. may be you can just use a cheap generic OBD-II scanner to clear it yourself (instead of taking it back to the shop) when CEL comes on.
 

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1999 SL500 R129
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97 Posts
Discussion Starter #8
Thanks! I’m going to see if a new gas cap gasket may be a solution. It’s cheap and can’t hurt. If that doesn’t work, I may go ahead and just replace the O2 sensors. Even though I only have 46k on the car, it is 20 years old. I mean, if I do that, the EGR valve is new and there are no vacuum leaks, what else can it be?
 

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2000 SL500, 2001 S600, 2004 E320
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548 Posts
I went back to the shop for the smoke test and code check; nothing. They cleared the code. Then, last night, it reappeared...
If they cleared the code there must have been a code. Which is it??? Sounds like they're not telling you everything. Maybe they just try to delete the codes and hope the problem goes away. Most of the time it will not.

Most CEL issues have two type of codes, stored and current. Current code may go away if the problem is borderline and intermittent. Stored codes stay in the memory until cleared by SDS.

I've never seen CEL on and no fault code or event memory.
 

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Premium Member
97 E-420 (180K miles), 97 SL500, (93K miles) 2015 GMC Sierra Denali 2500HD CC/SB/4x4 Duramax(55K)
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4,194 Posts
If they cleared the code there must have been a code. Which is it??? Sounds like they're not telling you everything. Maybe they just try to delete the codes and hope the problem goes away. Most of the time it will not.

Most CEL issues have two type of codes, stored and current. Current code may go away if the problem is borderline and intermittent. Stored codes stay in the memory until cleared by SDS.

I've never seen CEL on and no fault code or event memory.
yes, codes are either ones that trigger the CEL or "pending codes". Codes that indicate a malfunction but the malfunction must repeat within a certain period of time before they trigger the CEL. If they don't repeat the disappear. And some codes once cleared require a specific drive cycle before indicating a "ready" state that will pass state inspections. If it is in the "not ready" state it means the drive cycle has not been completed to verify the system thinks everything is now ok, and in most states that is the same as a CEL on, you don't pass. And some codes that trigger the CEL will go away if certain drive cycle indicates the fault has gone away. Some will not go away until erased even if the fault goes away.


our daughter has a 1996 car. (not mercedes) CEL came on and friends code reader says no codes, wouldn't erase any either. Not all code readers are created equal. My code reader showed the fault codes, pending codes and let me erase the codes. code was for a random misfire.

When the code came on again she took it to her friendly mechanic she trusted and his comment was that on her year and model vehicle many code readers would not read the codes hence not be able to erase the codes, others would say not codes found but would erase the codes and turn the CEL off. He had run into the problem with customers coming in. His code readers would read and erase the codes.
 

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1999 SL500 R129
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97 Posts
Discussion Starter #11
Solved! For the time, anyway... It finally threw a code for the MAF sensor. A relatively easy and cheap fix. Fingers crossed...

Thanks for all the input.

Ben
 
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