p0303 error code
11-11-2023, 02:02 PM
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p0303 error code
Hi Forum, I have a 2016 CLS 550 4matic which I purchased April 2020 from MB as a CPO with 29k miles. 2 years ago, at 55k miles, I had a p0305 error code (from Auto Zone reading). MB dealer read p035513 and p030585... misfiring in cylinder 5 caused by faulty coil. I had coil and spark plug replaced by dealer for $715 under warranty.
Just had check engine light go on now at 77k miles... 2 years later...and car ran rough like the last time. Brought it in to Prestige Motors in Ft Myers next day. Have heard good comments about this shop. Of course, car ran no issues and no check engine light on the way in. He said he couldn't get a code reading. No charge. Next day check engine light again and rough running. I bought a Innova 5210 reader and of course the car running fine. However, error code p0303 registers... Cylinder 3 misfire.
Questions...
1. Shouldn't the code been readable upon the 1st occurance?
2. All plugs were later replaced but now I am thinking what is the best course of action? Replace coil 3 and plug OR replace coils 1, 3 and 7 with plug 3 OR replace coils 1, 2, 3, 4, 6, 7, 8 and plug 3? Are these coil failures unusual one off items or will they all be going bad? Or do I need to wait for complete analysis as my Innova isn't getting all the details?
Thanks in advance,
Andy
edit... So I see now cylinder numbers on passenger side from front of car on the M278 engine is 1, 2, 3, 4 and on the drivers side from front of vehicle is 5, 6, 7, 8. So my question is different I guess?! 5 went before and was replaced and now 3 is in play on the other side. Input from members appreciated.
Just had check engine light go on now at 77k miles... 2 years later...and car ran rough like the last time. Brought it in to Prestige Motors in Ft Myers next day. Have heard good comments about this shop. Of course, car ran no issues and no check engine light on the way in. He said he couldn't get a code reading. No charge. Next day check engine light again and rough running. I bought a Innova 5210 reader and of course the car running fine. However, error code p0303 registers... Cylinder 3 misfire.
Questions...
1. Shouldn't the code been readable upon the 1st occurance?
2. All plugs were later replaced but now I am thinking what is the best course of action? Replace coil 3 and plug OR replace coils 1, 3 and 7 with plug 3 OR replace coils 1, 2, 3, 4, 6, 7, 8 and plug 3? Are these coil failures unusual one off items or will they all be going bad? Or do I need to wait for complete analysis as my Innova isn't getting all the details?
Thanks in advance,
Andy
edit... So I see now cylinder numbers on passenger side from front of car on the M278 engine is 1, 2, 3, 4 and on the drivers side from front of vehicle is 5, 6, 7, 8. So my question is different I guess?! 5 went before and was replaced and now 3 is in play on the other side. Input from members appreciated.
Last edited by ajv10; 11-12-2023 at 07:36 AM. Reason: update cylinder numbers
