ECM Input E.7.4 - Park/Neutral Switch Circuit: Notes

WARNING: This page is about a different car, the 1989 Cadillac Fleetwood and 1989 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

The park/neutral switch is a part of transmission Neutral Safety/Back-Up (NSBU) switch. Terminal "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 terminal A to ground. In any other gear range, terminal A is open to ground.

The ECM sends 12 volts to terminal 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 volts at ECM terminal A4. In reverse or forward gears, circuit No. 434 is open to ground resulting in 12 volts at ECM terminal A4. The ECM uses park/neutral status for fuel and idle speed control, and as a test condition for many trouble codes.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Checks for hard or intermittent fault.
Checks for fault in wiring or switch.
If E.7.4 passes by jumpering, fault is at switch or switch connector.
Checks for open to ground at switch.
Checks for ECM's ability to recognize a ground at terminal A4.