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Discussion Starter #1
Hi All

Background [this para can be skipped!]

My wife's first love suffers from a temperamental EML.
Initially this seems to have been caused by a defective heater in the front O2 sensor, which I replaced. I noticed oil in the connector and cleaned this as well. After a brief period of success the problem re-appeared and the O2 sensor was fingered again. So after finding deposits on the exhaust outlet [which may have come from a failed cat] I changed the cat. All was well for a time then the problem reappeared. After reading advice on this board I checked for oil leak from cam mag sensor and within wiring loom and again at O2 connector - some oil again at connector so cleaned it again, stopped any oil wicking with cotton around wiring but consider oil in connector probably gets in past the ring seal, and comes from aerosol discharge from transmission filler tube, so have lagged the connector with duct tape. But the EML triggers persist.

Present situation

My OBD2 scan tool in data stream mode shows that the P0130 [front O2 sensor voltage] code is triggering at about .45v whilst the engine is warming up. I believe that this should be .4v max. and if it was, there would be no problem. The operation of the sensor itself seems fine with readings above .5v, never below .45v, and rising to a steady 1.0v when at full operating temperature. So my query at the moment boils down to this - why is the EML triggering at .45v???? Is there a problem in the EMU??
 

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Welcome from the Sacramento Valley SLK Enthusiasts!

What's a EML?
 

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AND MABEL
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Hi, welcome from Barrhead, Scotland. :smile:
Sorry I can't help you with your problem, but one of the 170 guys surely will.
 

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Hi and welcome from the UK Midlands! :)

I can't help you with the issue you've described, but hopefully someone will be along shortly with some useful advice for you.
 

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I think most of us call it..."That stupid light is on again'
Probably CEL ' Check Engine Light'
 

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Isn't the front sensor supposed to fluctuate 0.2-0.8V once per sec?

I would find the source of the oil first!
 

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Discussion Starter #16
I've seen various figures for the voltages at which the EML lights up and this would seem to be a critical issue. Can you remember the source for your .2-.8?. I don't believe this is correct as the EML seems to be tripping on the low side - it's seems perfectly happy at 1.0V
I'm working on tracing the oil leak, taking note of posters here who reckon it's wicking along the wires. But in any case this does not seem to be affecting the performance of the sensor, which is reporting sensible readings i.e. no indication of electrical shorts.
On a trial run today I reset before starting out and drove 30 miles with no problem. However after cooling down and restarting for the return journey the EML tripped after the engine had reached full operating temp. and this seems to be a consistent behaviour i.e. no problem if reset before the journey but not happy for the next journey.
 

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Discussion Starter #17
EML Solution

My problems with the eml now seem to have been resolved.
The local MB main dealer was asked to provide a solution, and after half an hour's investigation said that the following was needed:
Replace EMU, replace wiring loom, renew camshaft mag sensor seal, renew O2 sensor. The estimate was £2000+.
As the list price of the car is £2800 this did not seem sensible, so I continued to monitor OBDII data through about 5 eml triggers - all caused by front O2 sensor [i.e.code 130]. As explained previously this sensor seemed to be performing reasonably although I had no experience of what the output should really look like. Eventually the same O2 sensor threw a code 135 - heater failure, which meant I could take it back to the supplier who had sold it a couple of months earlier.
The voltages produced by the latest sensor have a very different look about them i.e. are much more variable. And the car has now completed many short and 2 long journeys with no further problem:smile:. So problem solved.
So the original replacement sensor was defective, and no expensive MB-recommended repairs are necessary:surprise:!!!!!!!
My thanks to those who showed an interest.
 
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