Transmission Position Sensor/Switch: Testing and Inspection

WIRING DIAGRAM:

CHART C-1A

PARK/NEUTRAL SWITCH

2.8L & 5.0L "F" SERIES

FUEL INJECTION (PORT)

The Park/Neutral Switch contacts are a part of the Neutral Start switch and are closed to ground in park or neutral, and open in drive ranges.
The ECM supplies ignition voltage through a current limiting resistor to Ckt 434 and senses a closed switch when the voltage on Ckt 434 drops to less than one volt.
The ECM uses the P/N signal as one of the inputs to control:
a. Idle Air Control
b. VSS Diagnostics
c. EGR Control

Chart C-1A Park/Neutral Switch Diagnosis:

1. Checks for a closed switch to ground in park position. If using an ohmmeter instead of a test light the resistance will be low, indicating continuity to ground.
1a. Optional test (5.0L only):
a. Connect a test light across EGR solenoid connectors.
b. Engine at normal operating temperature and in park.
c. Accelerate to 1500.
d. Observe light.
e. Repeat test in drive and the light should go dim as engine is accelerated.
f. If both conditions are met then the P/N adjustment is OK, otherwise proceed with chart.
1b. Optional test (2.8L only):
a. Disconnect EGR solenoid electrical connector.
b. Connect test light across harness terminals A&B.
c. Engine at normal operating temperature.
d. Accelerate to 1500 rpm and note light.
e. Light should stay out.
f. Repeat test in drive.
g. Light should get brighter as engine RPM goes up.
h. If both tests pass then the P/N switch is OK.
i. If either test fails, proceed with chart C-1A.
j. If C-1A does not find a problem see EGR check chart C-7.
2. Checks for an open switch in drive range. If using an ohmmeter instead of a test light to 12 volts, the resistance will be high or infinity, indicating an open switch.
3. Checks to this point indicate the P/N switch and wiring are OK, however, the ECM signal voltage on ckt. 434 may be missing. To check, reconnect ECM. Either back probe ECM connector circuit 434 with selector in drive or disconnect P/N switch and probe harness connector ckt 434 with a voltmeter to ground.