hello all,

before, i used to have the misfire (P0300) code on cold starts, CEL keeps flashing for couple of minutes then it stops and then car acts normal and drives fine!, I drove the car in the morning and parked it in front of the house, came back at night and engine is not firing!!!, it cranks but does not start, i press the paddle and it fires for one second and little white smoke comes with (i think) fuel smell from the exhaust and then it shuts off!

now I'm getting this code only P0643 (Sensor Reference Voltage "A" Circuit High) , any idea what is this code? i searched in the forum and everywhere in the internet and cant find any information about it or a fix.

i was working on solving the P0300 code and i + the dealer changed a lot of parts but it did not fix it and now the car is not working at all!

this is what i have changed so far:-

-new spark plugs
-new ignition coils
-new engine temperature sensor
-new fuel pump
-new Thermostat
-new O2 sensors
-new battery
-new outlet water (dealer said need to change?)
-new Motor fan (dealer said need to change?)
-flush and tuned again!

what i have on the car is Gen3 intake + M370 intake manifold + pulley + LTH + cat-back

any ideas what is this code means?

 

Found this via google. May or may not be helpful.

OBDII Code P0643 INFINITI - Sensor Power Supply Circuit Short | HelpForCars.net

OBDII Code P0643 - Sensor Reference Voltage 1 Circuit High | Nissanhelp.com

I'd look this up in the fsm and what the troubleshooting involves. Don't have it on this computer.

From reading the above, it sounds like some key sensor is shorted or not reading a reference voltage that's in spec.

Not sure what the justification for a new water outlet or fan motor was. Maybe take it to someone that know how to perform a proper diagnosis.