Today I made an appointment with my Dealer. My truck is throwing a code P0191( fuel rail pressure). Service manager asked if the "check engine" light came on. I replied "no". He stated that they would look at it, but they most likely won't be able to fix the code until the "check engine" light comes on. Is this true? And if it is ,why even have codes?
Thanks
Odie

 

I don't think they can diagnose it unles the engine light stays on.
I know when I was having lack of power on my big truck with cummins n-14 460 they couldn't find what was causing it until one day the check engine light stayed on. Put there lap top on & found a bad air sensor that wouldn't let it build enough boost.

 

that is a bunch of bull , if we waited for these codes to keep a check engine light on continous then there would be lot more towed in trucks, that just mean you have a active fault code , they should hook up and check how many counts of the code you have and then go from there , we troubleshoot many inactive fault codes and sometimes get lucky and have the active fault codes those are the easy one's