Question Details

I’m having problems diagnosing code 0300 multiple misfires. On both banks. I’ve replaced all plugs and coils with Bosch. Can’t find any vacuum leaks. When it misfires I get the Drivetrain malfunction error. Any ideas??


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MBFanatic  4 months 3 weeks ago

Do you have any other codes? Also how many miles does it have? 

Is it possible for the ignition coil wires to be crossed? 

Those symptoms can also be caused by the mass air flow sensor and the catalytic converters. 

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gfarmboy67  4 months 3 weeks ago

Only other codes were for the cylinders that were misfiring 0304,0305,0307. It has 59,300 miles. Out of warranty of course. It has the on plug coils so they are ok. I did clean the maf sensors. What should I try on the catalytic converters? I even thought it could be the crank position sensor going out. What’s weird is the misfires come and go. I can clear the codes and the car runs fine for awhile. I unhooked both batteries to try and reset the ECU but now I’m getting a bunch of errors about the chassis stabilization and pedestrian warning sensors. 

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MBFanatic  4 months 2 weeks ago

Does the car struggle to accelerate uphill? That would indicate a bad cat converter. If there is a restriction on the cat, it will casue multiple misfires. You can perform a back pressue exhaust test. A muffler shop can do this for you or you can even do it yourself if you can get to the upstream oxygen sensor. 

You may also have a vacuum leak but that I would think would be picked up by the ECU and trigger the check engine light with a different code. 

What I meant with regards to the igntion coils is if two of the wires that go to the coils were swapped by accident??

Also did you have the codes before you changed the spark plugs? 

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