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david craig
david craig, ASE Certified Technician
Category: GM
Satisfied Customers: 539
Experience:  owner/mechanic at 3D Automotive
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Po300 has occured on my hummer h3 2006, intially my car over

Customer Question

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
Submitted: 6 days ago.
Category: GM
Expert:  david craig replied 6 days ago.

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 6 days ago.
thanks for the reply ..would tune up Help in this case?
Expert:  david craig replied 6 days ago.

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.

Expert:  david craig replied 6 days ago.

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....

Expert:  david craig replied 5 days ago.

do you still need assistance?

Expert:  david craig replied 4 days ago.


Customer: replied 4 days ago.
thanks for the response u hansewred my question
Expert:  david craig replied 4 days ago.

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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