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.

A: You may have got contaminated fuel from the...

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: crank no start problem

We need to start by considering the amount of repair work that has been done recently. It is always wise to double check those repairs made are still holding. A poor connection from one of the sensors your placed could...

Q: Van shaking and misfiring.

Hello, a P0300 is a general misfire code without pointing to any one cylinder. There should be more codes present indicating which cylinder(s) have a misfire condition. You are correct in stating that a misfire is a combustion concern. To...

Q: Oil in coolant.

Oil in your coolant is a bad sign. This usually indicates a leaking head gasket or cracked head. A cooling system pressure test and block test will be able to determine this. I suggest having a qualified technician, such as...

Related articles

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.