Check Engine Light Code P0300 On GM 2.2L and 2.4L

We have been seeing quite a few problems with the GM 2.2L and 2.4L engines. Mostly on model years 2005 through 2009. This engine is very common in the Chevrolet Malibu, Cobalt and HHR. As well as the Pontiac G5 and G6. This is the 4 cylinder. The problem I am going to talk about today is a check engine light and misfire codes.

Check Engine Light

Now, there are many, many things that can cause an SES light. Anything from a loose gas cap to any number of failed sensors. But this particular problem is with a computer trouble code P0300. This is a general engine misfire. For a particular cylinder, the code would be P0301, P0302, P0303 or P0304, as the last number refers to which cylinder is misfiring. On a scan tool we can actually watch the cylinder misfire. This problem can be caused by a faulty spark plug, malfunctioning ignition coil or ignition module, a plugged or restricted fuel injector or an internal mechanical problem.

Engine Misfire

The problem we are seeing with this engine is the misfire on a warmed up motor, only at idle. If you press the gas pedal just a little, the fault goes away. There is also no problem at higher speeds or steady driving or accelerating. Normally we mechanics would first look for a vacuum leak. This would cause the problem at idle any any motor. When no vacuum leak is found, the ignition and fuel system components are tested and shown to be working properly, then the next step is to look into an internal mechanical fault.(See Pictures Below)

There are a few test that can be performed to test the overall health of the engine. First would be a cylinder compression check. That is done by removing the spark plugs, disabling the fuel injector and ignition systems, and cranking the motor over with the tool installed. We watch the gauge for several things. First, how high the pressure jumps on the first revolution, and then what is the highest reading after a few seconds of cranking. Cylinders are compared to each other looking at both these readings. This will show the difference, if any, of compression between cylinders. That can give an indication as to what cylinder to concentrate on. But since we are using a scan tool to watch live data stream, we know which to look closely at. A compression test can be a little misleading. Low total compression can be caused by worn piston rings, incorrect valve timing, or valve and seat problems. Depending on the condition, this test may not show any abnormal readings.

Compression Test

In this case, the compression on one cylinder is a little low. Squirting a little motor oil in the cylinder and running the test again shows no improvement. If it had, we would suspect worn piston rings, as the oil would have helped seal up the piston rings and raised the compression, which is not what is happening in this case.

So the next test on this 2.2L or 2.4L, which is much more comprehensive, in what is called a cylinder leak down test. This is a little more involved. This entails removing the valve cover, loosening the camshafts (this is an overhead cam engine) and removing the rocker arms (also called followers)  to let the intake and exhaust valves come all the way up and seal the combustion chamber.

The the tools is installed to pressurise each cylinder with a regulated amount. What we do is look for a percentage of leaking of this pressure. A certain percentage of loss means there is a problem. So now we have to find what is leaking. Listening in several different places is what is needed to locate the bad part. Opening the throttle to listen for the leak in the intake side. Listening in the exhaust pipe will show a problem on the exhaust side. Either way, the cylinder head must be removed.

After removal, the valves and valve seats are inspected. A great test to find where the leak is, is to turn the head over and fill the combustion chamber with water, or even better, washer fluid. The blue color makes it easier to spot the leaking valve and or seat. See Pictures below.

2.2L and 2.4L Engine Cylinder Head With Leaking Valves Leaking 2.2L and 2.4L engine valves causing check engine light P0300.

The fluid is leaking past the exhaust valve seats and into the exhaust port. This is causing a sort of vacuum leak inside that cylinder. More specifically a lean condition. This is why there is a misfire at idle. Above idle, at faster engine RPM, there is no time for the cylinder to leak, so no engine misfire. The repair for this particular engine misfire is to replace the cylinder head and bad valves. This aluminum head is  not repairable, so replacement is required.

Again, this problem is specific to the 2005 through 2009 2.2L and 2.4L. So if you are having an SES light and misfire or rough idle, be sure your mechanic does a thorough inspection and diagnosis to avoid guessing and replacing parts. A simple tune up or sensor is not going to fix this one.


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16 comments to Check Engine Light Code P0300 On GM 2.2L and 2.4L

  • sparky7366

    well this is all fine and dandy but your not addressing a po300 even on accel and no other codes stored so I would assume that according to the diagnostic trouble tree that should be addressed first – since it is the most common problem and then I would adress the other problems as far as at idle only

  • ivory

    Wat could cause my 09malibu to misfire po300

    • ProTech

      A lot of things can cause that, and that depends on what engine you have. Could be anything from a bad spark plug or ignition coil, to a wiring problem.

  • kike jr

    hi i have a 2009 hhr 2.2 with cylinder 4 mysfire replaced spark plugs,coil packs, may u please help me.

  • anna

    Have a misfire on 1st cylinder..after I’ve changed the spark plug it went away for a few days but the check engine light came back on givong the same error. .it does it when its idle amd than when I take off..I’ve also changed seals suspecting a leak to the spark plug. .didn’t help.

  • Anonymous

    i have a 2005 cobalt and i was told it has low compresion after someone put something in my gas tank and the dealer ship is a joke. what is the problem. the dealer ship is jumping right to putting a new engine in. is their a cheaper fix

  • marissa

    i have an 2005 chevy cobalt and i was told it has low compression and this is after someone put something in my gas tank. The dealer ship is saying its probably my engine but they only looked at it for 30 mins. They claim there is nothing in my tank or lines. my car will start but just stalls right back out unless you hold the gas down.so is the dealership right or is it something other then my engine.

    • Sam

      It would have to be something very bad in your gas to cause l;ow compression= very unlikely. Possibly diesel fuel in the gas could have caused that.

  • mick

    2005 malibu, 2005, when engine is warm and not all the time, but temp guage just rises up past half, the engine will flutter at exhaust, loss of power, the cat was replaced. what do you think

  • larry

    did i just leave 1

  • Will

    2009 hhr 300 code. Shows up only when I start the car. Puff of smoke from tailpipe.

  • bullworine

    for pontiac g5 if engine lights comes on and code reader says p0010 , it means chassis and body ground r not properly connected or grounded ….

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