I have a 2008 G37S 6mt with 100K miles. The car has been throwing P0300 codes, 3 times in the past couple of months. I took the car into Infiniti and they checked it on their Consult and found a stored P0605 code ECM). They said the code was an old one, my question, does anyone know how long a CEL code can remain in the ECU? Two years ago I replaced the Automatic Speed Control Device (ASCD), under the clutch, because the car wouldn't start. There is a Infiniti TSB describing how this would cause a P0605 code. Since I don't have the Consult to clear the code, could this be the culprit causing false P0300 codes. Car does not run rough, stall, or lose power. I usually just clear the P0300 code and continue driving. Appreciate your feedback, thanks.

 

If it keeps throwing it after you clear it it is throwing it because it keeps happening.

 

I know that the P0300 code is coming back, but Infiniti could not find any problems with the car's performance and no reason for the P0300 code. They told me that my car is fine, except I have the P0605 code that is an old one and didn't reappear after they cleared it. They said that if the P0605 code comes back, they'll have to replace the ECU. They seem to think that there may be some connection between the P0300 and the old P0605 code. That's why I was asking how long these codes remained stored in the ECU if they are not cleared by the dealer. As I understand it, the ECU performs a random check of the systems at some point and I'm wondering if when it does do this check, it kicks out the P0300. Two techs worked on the car, both of them drove along with the service manager and they found absolutely zip.

 

Stealthee, thanks for the feedback. I've been frustrated with this issue for awhile and I was looking to find a resolution. I was thinking that there was some connection between the ASCD replacement and the P0605 / P0300 codes. Since the ASCD replacement was related to a start issue, my thoughts it could be a latent code causing the misfire code. After looking further into it, I can see that they are not related. The previous time I took the car into Infiniti for the misfire code they told me that my valve cover gasket was leaking. I believe that I have hit a dead end with the dealership. At least now, I know why the P0605 was stored and that I don't have an ECU replacement issue.