ECM Input Code EI74 - Park/Neutral Switch Circuit: Notes

The park/neutral switch is a part of transmission gear selector switch. Pin "A" of 6-pin connector on switch is park/neutral input for ECM and BCM. The park/neutral switch contacts are closed in park or neutral, shorting switch pin "A" to ground. In any other gear range, pin "A" is open.

The ECM sends 12 volts to pin "A" of gear selector switch over circuit No. 434. When gear selector is in park or neutral, the 12-volt signal from ECM is shorted to ground resulting in zero volts at ECM pin "A4". In reverse or forward gears, circuit No. 434 is open to ground resulting in 12 volts at ECM pin "A4".

A "HI" status on diagnostic display indicates that switch is open (not in park or neutral), a "LO" status indicates a closed switch (gear selector in park or neutral). The ECM uses park/neutral status for fuel and idle speed control, and as a test condition for many trouble codes.