Prizm L4-108 1.8L DOHC VIN 8 MFI (1998)
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 when the power steering system oil
pressure is high enough to cause an undesirable idle condition. The 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
Check for any of the following conditions:
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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.
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A PSP switch that does not open or a signal line shorted to ground may affect idle quality.
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Check for a malfunction in the IAC system if the PSP switch circuit is OK. Increase the engine idle speed using a scan tool to control the IAC
valve. Diagnose an IAC system malfunction if the IAC valve does not respond to scan tool commands.
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:
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Backed out terminals.
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Improper mating of terminals.
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Broken electrical connector locks.
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Improperly formed or damaged terminals.
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Faulty terminal to wire connections.
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Physical damage to the wiring harness.
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A broken wire inside the insulation.
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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 the PSP switch signal circuit for voltage from the PCM.
4. This step checks the operation of the PSP switch.
9. This step checks for a short to ground in the Diagnostic Request circuit. A short to ground in the Diagnostic Request circuit can cause the PCM to
ignore the PSP switch input. A short in the Diagnostic Request circuit will cause the IAC duty cycle and the idle speed to remain fixed.
