Q: 2009 nissan altima hybrid has p0300 with a drastic loss of fuel mileage

asked by on

My car got code p0300 a few days after a fuel overflow at a gas station due to faulty nossle. I took the car to Sears Auto center and the mechanic had the spark plugs changed and after a few days again the same code came back with more multiple cylinder misfires specially after pulling off the leg from the gas pedal like before. Also the fuel mileage dropped off drastically from 33.8 to 24 mpg. I came start the car all fine. No noise coming from the hood. car runs smooth otherwise. Check engine light keeps coming and going by itself every few days.

My car has 134867 miles.
My car has an automatic transmission.

There are a number of things that can cause poor fuel mileage. A faulty camshaft position sensor is one of them. The camshaft position sensor is a magnetic sensor that monitors camshaft speed to regulate ignition timing and fuel injection timing. It gathers and sends information about the car’s camshaft speed (and as a result the position of each piston) to the car’s electronic control module. This information is received by the computer, which then uses this data to further calculate the time of ignition and the timing of fuel injection required by the engine. When this is not working properly, you may experience a drop in power, poor idling, poor fuel mileage and problems starting the vehicle.

A clogged or dirty EGR valve may also cause poor fuel mileage. The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. Whenever you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases. Once the engine reaches operating temperature and speed increases, the valve, either through vacuum or electronic control will gradually open, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. When the EGR valve is clogged or dirty, as they are prone to, it may not function properly causing the engine to idle rough, stall at idle speeds, cause the car to get poor fuel mileage, or emit a strong smell of fuel due to excess hydrocarbons which also results in failing emissions tests.

A clogged or failing catalytic converter can cause the vehicle to have poor fuel economy. As you may already know, the catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable to be expelled into the atmosphere. When this is clogged, this causes these gases to be backed up into the exhaust system not allowing the engine to breathe properly. When this happens, the engine is forced to work much harder to expel these gases. This often results in the engine bogging down, hesitating, shaking and causing very poor fuel economy. I would recommend having a professional from YourMechanic come to your location to diagnose and inspect your vehicle.

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
  1. Home
  2. Questions
  3. 2009 nissan altima hybrid has p0300 with a drastic loss of fuel mileage

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: Axle shaft issue - 2009 Hyundai Santa Fe

Hi there. The dealer can say anything about the vehicle for other vehicles have had this issue, however, this is also a symptom of the transmission clutch grabbing hard when floating in between a gear selection range. Hyundai, Toyota, and...

Q: Brand new CV axles causing vibration?

An alignment will not cause a vibration but if one of the tires was out of balance this can cause the problem if on of the weights fell off during the axle service. Once you get all tires balanced see...

Q: Pressure Control Solenoid 'B' Control Circuit Range/Performance Read more: https://www.autocodes.com/p0965.html asked by Donald L

Hi there. The trouble code you indicated is similar in many ways to the P0963 OBD-II code. This article should give you a lot of valuable data that will explain the source of this code, possible causes and repairs. In...

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...
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.