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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > p0306 code for cylinder misfire and seatbelt extender problem (07 e92 335i)



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      02-11-2015, 04:40 AM   #1
twistedspoon
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p0306 code for cylinder misfire and seatbelt extender problem (07 e92 335i)

Hopefully this is the right subforum for this. Purchased an 07 E92 335i over the weekend. 114K miles which was a little higher than I wanted but the price was pretty good and last owner (second who bought CPO) seemed like he took care of it.

anyway, I got a "service engine soon" light so I scanned it with my bluetooth OBDII tool and got a P0306 code for engine misfire. I did some research and it seems like spark plugs are generally the solution for this problem.

I cleared the code with the Torque app on my phone and the "service engine soon" light disappeared when the car is on, but it shows up again when I start the engine. is this normal? or should I not worry about this until I get the new spark plugs in (hopefully they come in soon).


the other problem is that the seatbelt extender on both seats doesn't "catch" the seat belt properly, it just slides right by. any suggestions on a fix for that?

hopefully I'm on the right track with the P0306 code. please let me know if anyone has any suggestions.
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      02-11-2015, 04:48 AM   #2
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This might work for your belt butler...

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      02-11-2015, 01:45 PM   #3
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This might work for your belt butler...
i'll take another look at it and see if this is the problem. I don't think it is though, the problems seemed more that the folding part of the arm didn't fold out all the way. I'll take a video later today.
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      02-12-2015, 03:52 AM   #4
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didn't get to test the seat belt arm today but I did some research (aka read the service/owners manual).

it seems the car has a built in notification for when the spark plugs need to be replaced. that notification does not show up on my gauges; does this eliminate the spark plugs being the cause behind the p0306 code or is that not the case?
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      02-17-2015, 10:06 AM   #5
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Does the car stumble a little when starting up and then stabilize itself after a few seconds?

I used to have the P306 code, misfire cyl 6. I replaced sparks and coils. After all of that, I found out the problem was a leaking injector, so I had to replace that too.

You can do proper diagnostics before changing anything out. Swap sparks and plugs from cylinder6 to a different one. See if the error moves to the new cylinder. If it does not, start considering changing the injector.

There seems to be a way to diagnose injectors too. By measuring the voltage through them. Ive just read that in the forum, have never done it.
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      02-17-2015, 10:47 AM   #6
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I wouldn't rule out the plugs based on the service reminder. It could have been reset at some point without the plugs being changed out. Seems to me that putting in new plugs is a good place to start and if nothing else gives you the peace of mind of knowing how new/old they are.
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      02-19-2015, 01:53 AM   #7
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Originally Posted by vapore0n View Post
Does the car stumble a little when starting up and then stabilize itself after a few seconds?

I used to have the P306 code, misfire cyl 6. I replaced sparks and coils. After all of that, I found out the problem was a leaking injector, so I had to replace that too.

You can do proper diagnostics before changing anything out. Swap sparks and plugs from cylinder6 to a different one. See if the error moves to the new cylinder. If it does not, start considering changing the injector.

There seems to be a way to diagnose injectors too. By measuring the voltage through them. Ive just read that in the forum, have never done it.
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Originally Posted by jon_335 View Post
I wouldn't rule out the plugs based on the service reminder. It could have been reset at some point without the plugs being changed out. Seems to me that putting in new plugs is a good place to start and if nothing else gives you the peace of mind of knowing how new/old they are.


UPDATE - I changed out all the spark plugs and 1 coil (#6) and cleared the code using Torque. When I started the engine, the SES light was still on and rescanning the ECU continued to give me the P0306 code. The vibrating at 3000 rpms at high speeds has gone away (so it seems like it was a good idea to change the plugs out anyway), but now I'm noticing some very slight, weird shaking/jerking when idling that feels like it's coming from under the seat. Next step is injector? Sounds painful
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      02-19-2015, 08:55 AM   #8
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Procedure doesnt look painful. But you have to code the new ones in. Id say that is the worst part.(and Im a software engineer)
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