Roadmaster Estate Wagon V8-350 5.7L (1993)
cause an idle problem. Closing the switch causes circuit 495 to read less than 1.0 volt, and the ECM will increase the idle air rate and retard the timing. A
switch that will not close, or an open circuit 495 or 450, may cause the engine to stop when power steering loads are high. A switch that will not open, or
circuit 495 shorted to ground, may affect idle quality.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1.
This checks for an ECM voltage signal on circuit 495 and confirms that ground circuit 450 is OK.
2.
Maximum resistance, or infinity, indicates an open switch.
3.
Less than 1.0 ohm indicates that the switch is closed when the power steering pressure is high. Switch is OK.
DIAGNOSTIC AIDS:
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 495 shorted to ground will cause timing to retard at idle and may affect idle quality.
The power steering pressure switch input to the ECM will disable the A/C compressor clutch if circuit 495 is grounded or if the power steering pressure
switch is shorted internally.
