Q: What repairs fix codes P0172 and P0304? I just had all the spark plugs replaced recently.

asked by on

My check engine light has been on for about a month now. The vehicle seems to stall and feels like the engine loses energy sometimes or wanting to come to a stop. I had the check engine light checked and got codes P0172 and P0304 and was told to replace ignition coil for cylinder 4 and that spark plug. I just had all four spark plugs changed so is it necessary to replace that one as well? And should i replace all the ignition coils or just that one? Also what codes fix this if not the ignition coils?

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

The P0304 code indicates a misfire has been detected on cylinder 4. The P0172 code indicates that the fuel mixture is richer than the mixture control can compensate for. It’s possible that they are related, but not necessarily. Rich mixture can be caused by excessive fuel pressure, or sometimes by leakage at a fuel injector. If your misfire is caused by leakage at injector number four, then it’s likely that the two codes have a common cause. It’s also possible that you have had a spark plug foul because of a rich mixture. Again, that would be a common cause. But it is also possible that you have a failure in the number four ignition coil, they are not uncommon. In that case, the P0172 would be a separate issue altogether. If I were working on the car, I would try to determine the cause of the over rich mixture and then work from there. In any case, you need to have a qualified technician check this thing out. Contact Your Mechanic and they can send a technician to your home or office to check out your car and tell you what needs to be done.

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. What repairs fix codes P0172 and P0304? I just had all the spark plugs replaced recently.

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: Mercedes Misfire codes Po300 301 302 303

Ruling out ignition or fuel system problems is a lot of work. I usually do it by substituting components from non working cylinders to working cylinders to see if the misfire moves. Misfires on one side of the engine like...

Q: Codes P0171 and P0442 - is it a gas cap issue?

Hello. These "small leak" codes can be very frustrating! Both of these codes (P0171 - lean condition, P0442 - small evaporation system leak) are the result of an air leak in the engine's air intake system. Causes can be leaks...

Q: Engine sputtering after refueling

Hi There, This is likely related to your EVAP emissions system and something called a purge solenoid. The EVAP system prevents fuel vapors from the fuel tank from escaping into the atmosphere. The EVAP system collects and temporarily stores the...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
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...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...