Fuel economy drops by 40%, CEL on - Mercedes-Benz Forum
 
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post #1 of 2 (permalink) Old 01-20-2018, 07:04 PM Thread Starter
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Date registered: Jan 2018
Vehicle: 99 E430, 08 E63 AMG
Location: Kamuela, Hawaii
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(Thread Starter)
Fuel economy drops by 40%, CEL on

Sudden loss of fuel economy and CEL on. Hooked up the OBDII reader to discover code 0171 (bank 2). Bank running lean.
Researched to discover PROBABLE MAF sensor failure. Replacement part is available for about $200.
I didn't know how a MAF sensor worked, so began searches. During to search I discovered a post where it was explained that the sensor CAN get dirty, and it was suggested that a thorough cleaning would be the first step.
With a screwdriver, I gingerly removed the upper and lower clips that held the sensor in the airbox. I carefully withdrew the sensor then gave it a good spraying with MAF cleaner, then re-installed it. I cleared the DTC through my OBDII reader. I was concerned that there might be a little cleaner remaining inside the sensor, and considering there is a wire that heats up contained within the sensor, I gave it overnight to dry out, the cleaner being flammable.
Took the car for a 20 mile run. Fuel economy back up to >20 mpg.
Happy camper here.
Now I do understand that this might not be a long term fix, that the problem could return. If that happens I'll replace the sensor at that time.
bombguy54 is offline  
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post #2 of 2 (permalink) Old 01-26-2018, 12:34 PM
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Date registered: May 2016
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I had that same exact code on my former project S500 and a precipitous drop in fuel efficiency. Just like what you describe. Turned out to be a crankcase ventilation hose that had popped off. Oops.

I put that hose back on, and bye-bye, CEL. Now I need to reset the engine's adaptive computer to help speed up the relearning so it gets good fuel mileage again. 'Tis good to have SDS. :-)
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