Chart C-1E Power Steering Pressure Switch (PSPS) Check

Chart C-1E:

Power Steering Pressure Switch Circuit:

CIRCUIT DESCRIPTION
The Power Steering Pressure (PSP) switch is normally open to ground, and CKT 495 will be near battery voltage. Turning the steering wheel increases power steering oil pressure and applies more load on an idling engine. The pressure switch will close before the load can cause an idle problem.

Closing the switch causes CKT 495 to read less than 1 volt and the PCM will increase the idle air rate and retard the timing.

^ A pressure switch that will not close, or an open CKT 495 or 451, may cause the engine to stall when power steering loads are high.
^ A switch that will not open, or a CKT 495 shorted to ground, may affect idle quality.

CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Check for PCM signal voltage on CKT 495 and confirms that ground CKT 451 is OK.
2. Less than 1 ohm indicates that the switch is closed when the power steering pressure is low. Switch is faulty.
3. Maximum resistance, or infinity, indicates an open switch.

DIAGNOSTIC AIDS
A pressure switch that will not close, or an open CKT 495 or 451, may cause the engine to stop when power steering loads are high.

A switch that will not open, or CKT 495 shorted to ground, will cause timing to retard at idle, and may affect idle quality.