Q: Mercedes Misfire codes Po300 301 302 303

asked by on

I have PO300 301 302 303 misfire code. It is not ignition it is not fuel or injectors problem. It my be the computer but I do not think so. I think I have enjine mechanical fall. Please help me to diagnose.

My car has 150 miles.
My car has an automatic transmission.

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 this could be the result of a bad vacuum leak. So you’ll want to listen carefully for a hiss while the engine is idling. If you suspect a mechanical failure in the engine, you can check that with a compression tester and a vacuum gauge. Doing a compression test can give you an idea about the rings and valves, and with the vacuum gauge a good mechanic can determine if the camshaft is worn. Look carefully at the spark plugs for reddish deposits that might indicate head gasket failures. The control units do fail on these cars sometimes but they are very expensive and need to be coded by the dealer so you can’t by them from a salvage yard. So you want to be absolutely certain before you try replacing one. If you want a professional to check it out, Contact Your Mechanic, they will send a technician to your home or office to check out your car and tell you what you need to do to fix it.

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. Mercedes Misfire codes Po300 301 302 303

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: When driving at a steady rpm or passing speed, my truck hiccups really bad. I replaced the valve cover gaskets&harnesses already.

Hello. From what you described, it appears that your vehicle may be experiencing some sort of misfires. This can be caused by a few things. However, if the valve cover and harness have been replaced then they are likely not...

Q: Misfires, Rough idle, Engine Check light, and Engine not starting

Hello there, many different faults can cause your 2002 Chevrolet S10 to have starting issues, misfires and lack of power. The first step would be to scan the truck to determine what codes are present, this will determine what route...

Q: Q: The car starts then dies.

Hello there. In most cases, when there is a situation like yours when the car starts then dies, it's due to a fuel or ignition system failure. In some instances it is due to components like fuel injectors, Mass Airflow...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
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...