GL Class (X166) 2013-2015 after facelift became GLS (X166)

GL450 OBD Code P21A0 - Cylinder 5 Air-Fuel Ratio Imbalance Reply Subscribed

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Old Mar 22, 2021 | 12:59 PM
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GL450
GL450 OBD Code P21A0 - Cylinder 5 Air-Fuel Ratio Imbalance Reply Subscribed

I have about $3000 in two different mechanics trying to solve this code. I am not sure they are even looking in the right direction. Any help would be appreciated for ideas. I have researched the internet and found very little and explanations are all over the place. I live about 2 hours from the nearest MB Dealership so hoping to find just a good import mechanic that might have some luck. This is a 2013 GL450 with 79,000 miles. It has a rough idle but gas mileage seems consistent. Very well taken care of, all oil changes regular and filters.

Thanks,


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Old Mar 22, 2021 | 08:45 PM
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2017 GLE350 4MATIC
I would start throwing sensors and parts at it, in generally this order:

O2 sensors, all 4 of them
Mass air sensor
spark plugs if not done at 50k or 60k miles
coils and boots all 6 of them
cam position sensors all 4

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Old Mar 22, 2021 | 09:25 PM
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2014 GL550
Check compression or leak down on that one cylinder.
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Old Mar 22, 2021 | 09:52 PM
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Originally Posted by Ricardoa1
Check compression or leak down on that one cylinder.
This.
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Old Mar 24, 2021 | 02:17 PM
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Thanks for the advice. Will try these.
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Old Jun 7, 2021 | 04:55 PM
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Mercedes E550 4Matic
I just picked up and GL550 and this code popped up same day of delivery. 14 82k dropped her off the next day luckily I am under the 30 day 1000 mile warranty. Did this ever get sorted out? @ndhole
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Old Jun 9, 2021 | 01:29 AM
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2014 e550 coupe
Originally Posted by thelenswap
I just picked up and GL550 and this code popped up same day of delivery. 14 82k dropped her off the next day luckily I am under the 30 day 1000 mile warranty. Did this ever get sorted out? @ndhole

let me know what thet do for yours. 2014 e550 coupe same code.
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