Code EI74 - Park/Neutral (NSBU) Switch Circuit: Notes
The park neutral switch is a part of transmission neutral safety/back-up switch (NSBU). Pin A of the 6-way weatherpack connector on the NSBU switch is park/neutral input for ECM. The NSBU park/neutral switch contacts are closed in park or neutral, shorting NSBU switch pin A to ground. In any other gear range, pin A is open to ground.
The ECM sends 12 volts to pin A of NSBU on circuit No. 434. When gear selector is in park or neutral, the 12-volt signal from ECM is shorted to ground resulting in zero (0) volts at ECM pin B9. In reverse or forward gears, circuit No. 434 is open to ground resulting in 12 volts at ECM pin B9. ECM uses "PARK/NEUTRAL" status for fuel and idle speed control, and as a test condition for many trouble codes.
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- Status "Hi" at all times means that circuit No. 806. A 12 volt supply from ECM pin B9 is never being shorted to ground in park or neutral.
- Status "Lo" at all times means that circuit No. 806 12 volt supply from ECM pin B9 is shorted to ground in all gear selector ranges.
- The gear selector switch "P/N" contacts provide a ground in park and neutral. Test light should light.