Even if the CEL isn't on, if I put a code reader will I read some codes that don't neccesarily activate the CEL?

 

There aren't any codes on OBDII that will not set off the light

 

What codes are you seeing?? there is a p1000 code that stays with the system after the computer is cleared or battery is disconected this will stay for several drive cycles untill the computer does several diagnostic cycles, also ther can be pending codes, the computer is constantly checking things like fueltank integrity etc you could have a code P0442 evap failure the fuel cap starting to go bad or left loose when the computer checks the system it dedects a fault and remembers it the next time it is ok so no light is set but it remembers for 20 or sodrive sycles that it has seen a problem. after the 20 or so cycles the code goes away thats an example of a pending code.

 

My scanner reads pending codes as well, thats why I said that there aren't any "invisible" codes. Sorry, I forgot that the basic scanners don't read those always

 

no, i haven't checked yet, but i'm getting a rough idle and a little hessitation(?) on the gas pedal, but no code.

 

When i installed a remote starter on my nav, I was getting a weak signal from the COP that I used for a tach signal that caused an intermittant hesitation (always at the worst possible time) and I couldn't get it to stop. The problem was a weak signal on that COP so I took off the remote start and the problem resolved itself.

 

You can have codes set without having the SES light come on.

JMC