The subject codes have been a PITA for several month's, believe that I have finally solved the problem. The P0300 code was thrown several times and after changing out COP's, swapping MAF's (since the misfires were coming from the #1 bank), and replacing upstream air/fuel sensor, the code eventually came back. I have had the car in at Infiniti and they told me that my valve cover gaskets were leaking. Had the VC gaskets changed out at Nissan for about half of what Infiniti wanted. Still had the p0300 and C1109 (low voltage) codes. Changed out the bank 1 O2 sensor and that seemed to help, no codes for a week or two and than it popped back on. Since I was still getting the C1109 code along with the P0300 code decided to let my battery charge overnight, even though Infiniti told me it was fine. Used my multi-meter to read the battery voltage in the morning and found that the battery was at 11.8V, which means the battery is not holding a proper charge. (It's supposed to read above 12.6v when charged). Took the car to Infiniti and told them to change out the battery, they told me that there was no problem with the battery. Had them change it out anyway, voila, no reoccurring P0300 or C1109 codes! Not sure if this is going to help anyone out there with the same codes, but I wanted to share this since so many of us have had the P0300 drive us nearly insane. One other note, Infiniti wanted to change out the ECU for $2K+ to take care of the codes.

 

Wow. Unreal experience. Noting for future reference. Glad its sorted.

 

I noticed that every time that I got the P0300 code I also had the C1109 code. That's how I finally decided to charge the battery overnight to see what the charge was in the morning. When I saw 11.8V, I knew it was a battery problem, even though it was showing good with my obdii reader. You need to use a multi-meter to get the correct battery voltage. I checked the new battery the following morning and it was sitting at 13.2v. Our cars have a alternator delay where it doesn't begin to charge the battery until you have driven 14 miles. If you only take short trips, the alternator will seldom kick in. Running in the cold weather probably makes the condition worse. Cold zaps the battery and additionally, you are using the heated seats, lights and heater. They are all operating on battery voltage. When I first got the car, I had the battery die a couple of times and bought a lithium battery to jump start the car if it happened again. That's when the dealer told me about taking short trips with the car kills the battery. So hopefully if anyone sees these two codes, it may be the battery not providing the right current to the sensors.

 

" Our cars have a alternator delay where it doesn't begin to charge the battery until you have driven 14 miles."

Ruh-roh. No wonder my battery seems to be a bit low on charge. I would think the ECU would by-pass that if the battery got down to a certain voltage.

 

^^Where is this documented? I have one of those cig lighter volt meters. Anytime the engine is running, it's reading around 14.x V.

No battery issues here - battery tender is connected most of the time.

 

I guess the proper term is ECM controlled alternator. When I first joined this website several years back there were several people having problems with their batteries. The reason was the charging delay set in the ECM. Here is a video on how to eliminate that issue:

 

Maybe this is something more common on the older models. My '12 doesn't exhibit this behavior. I started using the battery tender earlier this year (what's left of it). Before then, the car would sit, sometimes for weeks at a time without getting driven. It would start right up. Granted, the battery was not in the greatest condition because on a very cold day (teens/low 20's) last winter the car did fail to start requiring a jump. Battery was still weak even after driving for about an hour at hwy speeds.

Our honda otoh, always has this behavior. Having ac, headlights, or other electrical draw wakes the alternator up, otherwise it puts along as battery voltage. All in the name of .1 mpg savings.

 

That may be true, my car is a 2008. Since I had the battery problem, I also have a battery tender on the car. The battery I replaced was almost 5 years old, so I did get the expected life out of it. I will be keeping this one on trickle charge when it sits more than a few days. When I saw the 1.4V discrepancy between the old battery and the new one, after charging, I knew I found the problem. I have been monitoring the OBDII readings (cylinder misfires) and it looks good on all 6.

 

Thanks Glenn2008, your post helped me greatly!
I have a 2011 6MT sedan, which with the recent cold weather threw a SES light with P0300 code, when I was headed home from work. My commute is only 10 miles 1-way and the combination of the short commute and the cold weather must have lowered my battery voltage level. I've been researching what the issue could be on various threads and ordered a higher end ODB2 reader as well.
Incidentally, today, even though we have about 5 inches of snow and high of 19 deg, i had to take a detour and pick up someone, which kicked my commute beyond the 14 miles threshold. Got to my destination, shut the car off and when I got back in the car and restarted the car, the SES light was gone...
I'll have to make a point to take the car for a drive beyond the 10 miles in the future, from time to time.
Good stuff!
Cheers!

Jim