Testing and Inspection for Computer Command Control - Port Fuel Injection: Page 773
Chart C-1A Wiring Diagram
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:
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Idle Air Control
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VSS Diagnostics
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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 mis-adjusted switch in drive range.
DIAGNOSTIC AIDS:
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If CKT 434 indicates P/N (grounded), while in drive range, the EGR would be inoperative, resulting in possible detonation.
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If CKT 434 always indicates drive (open), a drop in the idle may exist when the gear selector is moved into drive range.
