My CEL comes on periodically and I am confused by this. I normally get the Code P0101. It means that there is a faulty signal on the Mass Airflow (MAF) signal and for that I have cleaned the MAF with special MAF sensor cleaner, replaced the boost pressure control valve, and even the replaced the fuel pressure sensor/guage.


But.


It still comes on with the P0101 flag.


The only thing left to do is replace the MAF sensor with a new original
Volvo unit or recheck the connecting tubes to it.


I do not know how many tubes there are and where they are located so I guess the first task is to replace the "Tru Part" MAP which is what is in my 2002 Volvo S40 now, with the original Volvo part or at least a respectable brand such as a Bosch.


Anyway if that does not work then the last task is to check the connecting tubes to the MAP sensor.


Now on the last CEL message I got two new codes. They are P0301 (Misfire Cylinder 1) and P0303 (misfire detected Cylinder three).


I am not sure what is the difference between a misfire on a cylinder and a misfire detected on cylinder 3. It seems the messages are exactly the same (but on different cylinders), but the change in the wording is not clear.


Anyway, how do I deal with these last two messages) P0301 and P0303? I thought that I saw something on the forum about checking ignition coils, but I am not sure.


Is there one coils to a cylinder of one coil to more than one cylinder?


Are these last two messages from my OBD II related to the first one, P0101?


Any help appreciated. Thanks in advance.


Respectfully,


Lou_Reed

 

On the gen 1 S40s (ie 2000-2004) there is one coil for two cylinders . Misfires can be caused by plugs (OEMs or basic copper core work best), weak or damaged connectors to the coils or the coils themselves. Misfires can also be caused by a slightly off mixture or bad fuel - but mixture problems typically show other codes. check the wires under the cover - the looms can go bad as well so you may want to clean up that too. I'd probably start by throwing in new plugs.

 

As you say, there is one coil for two cylinders. I guess (I hope) that the misfires in cylinders 1 and 3 can be taken care of by replacing just one coil. Is this possible?


Any help appreciated. Thanks in advance.


Respectfully,




Newport_j

 

the coils are designed to have one direct connection to a plug and the second connection via a wire. You need to remove the coils to install new plugs (they are held down by 10mm bolts). remove the bolts, the connector and it pulls straight off. I'd start by replacing the plugs and when the coils are off, inspect the connector for any cracks or corrosion. You can reinstall and see if the codes reappear. If they do, then I'd replace both coils and the spark plug wires and you'll be good for another 100K miles. for me, when I replaced the plugs I was shocked how old they looked. Codes never reset with the new plugs so I walked away with a $10 repair bill.

 

It's a 50/50 coin toss. The problem with misfires are the hairline cracks in the plastic that fits down over the spark plugs. If the cracks are on the coil then replacing the coil fixes the short circuit. If the cracks are on the plug that does not have the coil then your misfire will not go away by only replacing the coil. I went the cost efficient route (i.e. cheap) by coating the spark plug leads with RTV to cover the cracks in the plastic. It's worked so far.