Question by -R: GM Flex fuel experts Flex fuel sensor question?
I Have a 2002 GMC Yukon 5.3l truck with a error code P0178.
I checked the voltage at the connector to the sensor, and got 5.0v from pin one, 4.3v from pin 2, and pin 3 is ground. I know that pin 2 is supposed to be 12v. Does anyone know where the source voltage comes from for this sensor? Does it go direct to the computer, or is there a flex fuel module someplace? I don’t want to replace the 500$ sensor, if that is not the problem. Clearly its a problem with source voltage. Any help would be greatly appreciated!
Answer by jesse
Source voltage comes directly from ECM1 fuse 10amp in the underhood fuse block, Yes u should have 12V at the pink wire with key ON.
White wire is 5 V reference.
Black is ground.
No separate module for the fuel composition sensor.(computer controlled).
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