Skip the auto shop - Our mechanics make house calls

Q: rough idle, heavy missing, fault codes P0301 and P0456. lack of power, where do i start to diagnose this?

asked by on

had been travelling a little bit today, everything was going fine, shut off the car to visit a business. came back out and it started to misfire really really bad, then my check engine light came on and I got the fault codes listed in the title. extreme loss of power, heavy shaking. cylinder specific fault code which is rare for the car so far since I've had it. the gas cap seems to be fine as well as the filler neck. Was just wondering what could cause these issues and where I would start diagnosing it.

My car has 150000 miles.
My car has an automatic transmission.

Hi there. From the description you have provided, for the P0301 rough idle and heavy misfire and P0456 evaporative small leak detected, the problems are unrelated. The P0301 is a #1 cylinder misfire code. It could be, a spark plug failure or an ignition coil has failed. It could be, a fuel injector failure or a cylinder compression problem, ie; valve train or piston issue. The P0456 is a small leak detected in the evaporative system. It could be, a faulty fuel cap. A visual inspection may appear okay but, does not seal the deal. It could be an evaporative vent solenoid not sealing or a faulty evaporative purge solenoid. With all of the possibilities that could be causing your vehicle’s misfire and evaporative small leak, I recommend having your vehicle’s Check Engine Light be diagnosed and repaired by a certified technician, such as one from YouMechanic.

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. rough idle, heavy missing, fault codes P0301 and P0456. lack of power, where do i start to diagnose this?

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: Misfire codes and no-start. What could it be?

Fault codes for P0300, P0301, P0302, etc. indicate misfires. P0301 would indicate cylinder #1 misfiring, P0302 would indicate cylinder #2 misfiring,etc. Code P2159 has to do with the VTEC system malfunction. If all this started after the timing belt replacement,...

Q: Code P0456

Hi, thanks for writing in. I'd be happy to help. The P0456 code is for a small leak and the only way to find such a small leak is to have the system pressurized using the test port under the...

Q: I have a 2006 ranger and recently the car started loosing power and it wouldn't drive check engine light came on and it dia

You will need to have a compression test and ignition test on the three cylinders showing misfire. You may have jumped timing or lost compression in those cylinder. A six cylinder engine will not run correctly on three cylinders. Have...

Related articles

How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
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...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.