Firebird V8-305 5.0L VIN F FI (1987)
CHART C-1A PARK/NEUTRAL SWITCH DIAGNOSIS (AUTO TRANSMISSION ONLY)
Circuit Description:
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:
Idle Air Control
VSS Diagnostics
EGR
If CKT 434 indicates P/N (grounded), while in drive range, the EGR would be inoperative, resulting in possible detonation. If CKT 434 always indicates
drive (open), a drop in the idle may exist when the gear selector is moved into drive range.
Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1.
Checks for a closed switch to ground in park position. Different makes of "Scan" tools will read P/N differently. Refer to operators manual
for type of display used for a specific tool.
2.
Checks for an open switch in drive-range.
3.
Be sure "Scan" indicates drive, even while wiggling shifter to test for an intermittent or misadjusted switch in drive range.