Skip the auto shop - Our mechanics make house calls

Q: My Hummer shows code P0300 after getting gas

asked by on

Put 40 bucks of gas in tank from same place as always super America. Got on freeway about 10 min on freeway check engine light came on. Stopped at orileys to check code and got p0300. Random misfire drive home. When on freeway could feel the loss of power. I have good oil pressure not overheating truck starts no problem idles slighty ruff.

My car has 173000 miles.
My car has an automatic transmission.

You may have got contaminated fuel from the gas station. The code P0300 indicates you are getting a random engine misfire. This random misfire does not point to any one cylinder misfire and indicates that the fuel may be contaminated with something like water. All gas stations have some water that is in their tanks in the ground. The water normally sits in the bottom of the tank and if it becomes excessive then the gas station will need to have it removed. Now if there is about 2 inches of water in the tank settled on the bottom of the tank and the refueling truck dumped new fuel in the ground tank then water will temporarily mix with the new fuel for about an hour. If you happen to get fuel at the time the water is mixed up in the tank then you would get some in your tank. This water will cause erratic running and misfires in the engine. If you go to the parts store and get some dry gas additive it will disperse the water so you can run it through the engine and as soon as you get to half tank then refill tank again to disperse the water more until the engine starts running better. Then you can get the Check Engine Light cleared.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. My Hummer shows code P0300 after getting gas

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: 2003 Volvo V40 shudders and shakes when idling. When rpms go from high to low, or I start car when engine is warm, it stalls.

Have the computer first checked for any stored codes to see if it has detected the problem so it can be diagnosed. Check the air intake hoses from the air filter all the way to the throttle body for any...

Q: cylinder misfire

There seems to be a variety of symptoms going on at the same time. Addressing the ticking issue, it could be your lifters, and it could also be your fuel injectors. This could be part of the problem when it...

Q: Hi I have hummer h2 06 there is sign come on screen low oil pressure I changed sensor also changed fuil pump Engine runs smooth ha

Oil pressure can be tested and verified against factory specifications using an external pressure gauge, connected to a threaded access port on the engine block. If pressure measures normal, and the engine otherwise functions normally (adequate and even cylinder compression,...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...