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

asked by on October 25, 2016

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?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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

p1516 code on 03 v6 mustang. what should i ask to be fixed?

Although a diagnostic would have to be performed, the code you are reporting is usually a consequence of a fault in the intake manifold runner control (IMRC). To rule the IMRC system in or out, the recommended diagnostic is an...

Brakes squealing

This circumstance is not unusual and I suspect is often related to the use of non-OEM rotors and brake pads and also the failure to re-apply factory specified shims and/or appropriate anti-squeal compounds and lubricants. Unfortunately, once non-OEM parts and...

Engine noise and has no power. It spits and sputters.

Hi there. Sounds like the fuel pump is not working in your vehicle. Check the fuel pump relay and see if it is clicking on when the key is turned on. If the relay is working, then turn the key...

Related articles

P2431 OBD-II Trouble Code: Secondary Air Injection System Air Flow / Pressure Sensor Circuit Range / Performance Bank 1
P2431 P2431 code definition Secondary Air Injection System Air Flow / Pressure Sensor Circuit Range / Performance Bank 1 What the P2431 code means The secondary air injection system is used to add air into the exhaust to reduce vehicle...
P0552 OBD-II Trouble Code: Power Steering Pressure Sensor Circuit Low Input
P0552 means there is an issue with the power steering pressure sensor circuit often cause by failure of the steering pump or poor wiring/connection.
P0330 OBD-II Trouble Code: Knock Sensor 2 Circuit Malfunction (Bank 2)
P0330 code definition P0330 is a general OBD-II trouble code that is indicating a malfunction in the knock sensor circuit 2. Note:...