Serial # F187V17129

I have code 135-16. It's a Vortec 2400. the code description says "Fuel Absolute Minus (MAP) Too High"
What I'm not sure is whether this is the sensor in the fuel rail, or the MAP sensor in the intake.
The sensor in the intake is a 4 wire.so I assume it's a temp and pressure sensor.
Return (Green wire) is good.
The Red wire is 5v, also good.
One White wire has a steady 2.6 volts (probably the temp signal wire)
One White wire has about 2 volts at idle, and when you snap the throttle, it goes to approx. 4 volts to 1 volt, the back to 2 when it idles. seems to be working to me.
The sensor in the fuel rail is a 3 wire. 5V reference (RED) and return (GREEN) check out. The signal wire is approx 2.6V at key on and idle. It does go to 3.3V at immediate key off.
Any direction with this would be greatly appreciated.