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Engine misfire, fault code U0303

Tiny
LIAM MCCAULEY
  • MEMBER
  • 2004 BMW 320I
  • 2.0L
  • 4 CYL
  • 2WD
  • MANUAL
  • 85,000 MILES
The car listed above petrol, car was running fine then all of a sudden an engine misfire and not pulling worth. Fault code is U0303 for transfer case module incompatibility. Where am I looking to start?
Monday, February 12th, 2018 AT 1:18 PM

8 Replies

Tiny
STEVE W.
  • MECHANIC
  • 12,958 POSTS
Are you sure the code is not P0303? That code would indicate a misfire on cylinder three. That could be coil/wire/plug or internal engine issue. Easiest way to diagnose which would be to swap each part into a different cylinder one at a time and see which part causes the code in a different cylinder. Or just replace all the plugs with new and start there. Your choice.

The U0303 code would make sense if this was a four nwheel drive.
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Tuesday, February 13th, 2018 AT 7:05 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,861 POSTS
Hello,

These codes can be caused by a shaft speed sensor that is out of range. Here are the sensors locations. I would try the sensors first

Check out the diagrams (below).

Please let us know what you find. We are interested to see what it is.

Cheers, Ken
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Tuesday, February 13th, 2018 AT 7:13 PM
Tiny
LIAM MCCAULEY
  • MEMBER
  • 4 POSTS
Is this for the manual gearbox?
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Wednesday, February 14th, 2018 AT 8:31 AM
Tiny
LIAM MCCAULEY
  • MEMBER
  • 4 POSTS
Thanks for the reply! Yes I am sure it is u0303, but like you said it is not four wheel drive. Possibly maybe the code reader I am using? It is more of an engine misfire so it sounds as though it could be p0303.
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Wednesday, February 14th, 2018 AT 9:05 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 42,861 POSTS
My bad, I did not see the transmission type. I would go with what Steve W. Has suggested.
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Wednesday, February 14th, 2018 AT 10:32 AM
Tiny
STEVE W.
  • MECHANIC
  • 12,958 POSTS
If you are using a simple code reader most of those won't even read a U code, so I would bet it's supposed to be a P0303
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Wednesday, February 14th, 2018 AT 12:59 PM
Tiny
LIAM MCCAULEY
  • MEMBER
  • 4 POSTS
Okay, thanks, I presume a faulty maf sensor wouldn’t cause this?
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Thursday, February 15th, 2018 AT 12:52 AM
Tiny
STEVE W.
  • MECHANIC
  • 12,958 POSTS
It could but if it's a bad MAF I would expect a multiple random miss code (P0300) and a MAF code as well. You could try disconnecting the MAF and see if it uses substituted values to run better. Some will some won't.

Might want to have a shop pull the codes with a different scan tool and see what that shows. Would be real good if it displayed live data for the MAF flow rates and misfire counters.
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Thursday, February 15th, 2018 AT 1:05 AM

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