Fleetwood FWD V8-273 4.5L (1988)
DFI Crank Signal Switch Circuit
DESCRIPTION:
The Park/Neutral switch is a part of the transmission Neutral Safety - Back-up Switch (NSBU). Pin "A" of the six-way weather pack connector on the
NSBU switch, is the park/neutral input for the ECM. The 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.
The ECM sends 12 volts to pin "A" of the NSBU on CKT 434. When the gear selector is in park or neutral, the 12 volt signal from the ECM is shorted
to ground, resulting in 0 volts at ECM pin "A4". In reverse or forward gears, CKT 434 is open to ground, resulting in 12 volts at ECM pin "A4". The
ECM uses park/neutral status for fuel and idle speed control and as a test condition for many trouble codes.
NOTES ON FAULT TREE:
1.
Checking for hard or intermittent fault.
2.
Checking for fault in wiring or switch.
3.
If E.7.4 passes by jumpering, the fault is at the switch or switch connector.
4.
Checking for open to ground at the switch.
5.
Checking for ECM ability to recognize a ground at terminal A4.
NOTE ON INTERMITTENTS:
Check for NSBU switch out of adjustment.
Check for trans shift indicator out of adjustment.
Check for open or short to ground in CKT 434 between ECM and switch.
Check for open to ground on switch pin B.