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david craig
david craig, ASE Certified Technician
Category: GM
Satisfied Customers: 3316
Experience:  owner/mechanic at 3D Automotive
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Po300 has occured on my hummer h3 2006, intially my car over

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po300 has occured on my hummer h3 2006
JA: Are you fixing your H3 yourself? What have you tried so far?
Customer: intially my car over heated and the check engine light came ..took it to the dealer said it was a radiator leaking..just replaced radiator today but check engine light is still on
JA: Does the light stay on, or does it blink?
Customer: it stays on
JA: Anything else you want the mechanic to know before I connect you?
Customer: no thanks

Hi Im David thanks for visiting the site. your code is for a ramdom misfire and could be caused by any spark plug, coil pack or fuel injector

Customer: replied 10 months ago.
thanks for the reply ..would tune up Help in this case?

yes a tune up never hurts. but keep in mind replace the plugs and coil pack may not fix the vehicle s code if an injector is causing the misfire.

the best way to tell which cylinder is misfiring is to have the engine running and one at a time unplug a coil pack if the engine doesnt stutter then thats the faulty coil pack. if it stutters put the conector back on and go to the next one.etc....

do you still need assistance?


Customer: replied 10 months ago.
thanks for the response u hansewred my question

i hope you were able to fix your vehicle. please accept the answer and leave a 5 star rating for me if you were satisfied with my assistance. thanks. have a nice night.

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