PSP Switch Diagnosis

Circuit Description
The Power Steering Pressure (PSP) switch is normally open to ground. Turning the steering wheel increases power steering oil pressure. Increased power steering oil pressure puts an additional load on the engine that may be noticeable at idle. The PSP switch closes before the load on the engine causes a undesirable idle condition. The powertrain control module (PCM) increases the throttle valve opening in order to maintain acceptable idle quality and prevent an engine stall.

The voltage signal from the PSP switch to the PCM indicates less than one volt when the PSP switch is closed. The voltage signal is near battery voltage when the PSP switch is open.

Diagnostic Aids
A PSP switch that does not close, or loss of ground at the PSP switch may cause the engine to stall when power steering loads are high.

A PSP switch that does not open or a signal line shorted to ground may affect idle quality.

An intermittent malfunction may be caused by a fault in the power steering pressure switch electrical circuit. Inspect the wiring harness and components for any of the following conditions:
^ Backed out terminals.
^ Improper mating of terminals.
^ Broken electrical connector locks. Improperly formed or damaged terminals.
^ Faulty terminal to wire connections.
^ Physical damage to the wiring harness.
^ A broken wire inside the insulation.
^ Corrosion of electrical connections, splices, or terminals.

Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
3. This step checks for voltage from the PCM or for an open or a short to ground in the PSP switch signal circuit.
4. This step checks for a poor ground connection at the power steering pump or a faulty PSP switch.