I've seen several threads on this code and my truck still has me stumped. The truck starts and runs but has a slightly rough idle (not like a whole bank being out but maybe 1 cylinder). Hooked my cheap scanner to it and it throws the p0603 and p1670 codes. I know that this is lack of communication between the PCM and IDM. My question is if the IDM is bad then the truck would not run at all, or could it cause a single misfire? So with all fuses and relays being checked, does that only leave me with the issue being a bad PCM? Or are there some other things I can check first. Any help is much appreciated, thanks!

 

Have you cleared the codes and verified they come back every time? Sometimes you get phantom codes that get stored in the PCM. Sometimes a battery voltage issue (P0603) also trips a P1670.

Can you buzz test the cylinders or read perdels with your scanner? Have you checked and cleaned all the battery cables (both ends of each cable)?

 

I second running the buzz test. That is what I would start with. A lot of the quality scan tools are able to perform this.

I have only seen the P1670 code pop up a few times. And in most cases the truck ran fine. If you have gone through everything, the PCM and or IDM may be to blame.

Are you running any kind of aftermarket chip/programmer?