Suburban 1/2 Ton 2WD V8-454 7.4L (1987)
Wiring Diagram For Chart C-1A - Park/Neutral Switch Diagnosis
CHART C-1A - PARK/NEUTRAL SWITCH DIAGNOSIS
Circuit Description:
The Park/Neutral Switch contacts 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
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 or reverse range.
3.
Be sure "Scan" indicates drive, even while wiggling shifter to test for an intermittent or misadjusted switch in drive range.
Diagnostic Aids:
If CKT 434 indicates PIN (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.
