Lumina L4-151 2.5L (1991)
Wiring Diagram For P/S Switch
CIRCUIT DESCRIPTION:
The Power Steering Pressure Switch (PSPS) is normally open to ground, and circuit 495 will be near battery voltage. Turning the steering wheel
increases power steering oil pressure, and engine load. This causes the idle speed to change. The pressure switch will close before the engine load can
cause an idle problem. Closing the switch causes circuit 495 to read less than 1 volt, and the ECM will increase the idle air rate and retard the timing. A
pressure switch that will not close, or an open circuit in 495 or 450, may cause the engine to stall at idle when power steering loads are high. A switch
that will not open or circuit 450 or 495 shorted to ground, may affect idle quality and will cause timing to retard at idle.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1.
This test checks for an ECM signal voltage on circuit 495, and confirms that ground circuit 450 is OK.
2.
Maximum resistance or infinity indicates an open switch.
3.
Less than 1 ohm indicates that the switch is closed when the power steering pressure is high. Switch is OK.
