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Power Steering Switches
What Technicians need to know about hydraulic Power Steering Switches and Pressure Sensors to assist when diagnosing and testing suspect switches and related circuit faults on the vehicle.
Power Steering Switch (PSS)
The General function of the Power steering Switch (for the engine management system) is to monitor the increased hydraulic pressure that is created when the steering wheel is rotated or held in a steering assist position, to allow the PCM to adjust the engine RPM to compensate for the increased engine load. The 2-terminal pressure switch generally results in an ON/OFF operational state that is pressure activated.
Failure to correctly determine when the hydraulic pressure increases or decreases during a steering or non-steering manoeuvre may create an increased RPM condition at Idle due to overcompensation or intermittent engine stalling due to under compensation for the increased engine load.
This condition may result in a typical Fault Code logged.
Generally: P0551 – Power Steering Pressure Switch Circuit Range/Performance.
Testing Procedure (PSS)
A suitable scanner may be utilised to check the switch operation during increased and decreased pressure cycles as the steering wheel is rotated as required.
A multimeter can also be utilised at the switch to monitor the ON/OFF performance as the:
- Steering wheel again is rotated as required.
- Switch is in a closed position; an expected result should indicate an earthed reading. (as near as possible to 0.0V)
- When the switch is in an opened position, an expected result should indicate the full circuit reference voltage.
(Example – FG Falcon = 12V indicating a loaded steering to the PCM)
Typical fitting locations for the Power Steering switches or pressure sensors are generally:
- On the power steering pump assembly.
- Or typically on the power steering pressure hose.
Power Steering Pressure Sensor (PSP)
The PSP sensor like the pressure switch (PSS) also monitors the power steering load. The sensor transforms the varying power steering load into a varying output voltage that is utilised by the PCM to assist in activating the throttle control system for a more stable RPM/load result.
A typical Toyota PSP sensor circuit indicating 3 terminals required for operation
PSP sensor Terminal 1 – Ground
PSP sensor Terminal 2 – Output voltage
PSP sensor Terminal 3 – Reference voltage supply from the PCM. (Typically, 5V)
A failed PSP sensor may create similar driveability conditions as the PSS. It is important for the technician to ensure the reference supply voltage and the ground circuit is plausible to eliminate any unnecessary parts replacement.
A typical PSP fault logged may be: P0550 – Power Steering Pressure Circuit Malfunction.
Test procedure for PSP Sensor
A suitable scanner again may be utilised to monitor PSP sensor operation. The expected output results vary compared to the power steering ON/OF switch. A gradual increase in voltage as the steering wheel is rotated indicates the sensor plausibility.
A typical faulty PSP sensor may indicate an output voltage of approx. 0.22V at all times as the steering wheel is rotated, and power steering load has increased.
Note: a suitable oscilloscope may also be utilised to test the PSP sensor by monitoring the output signal during the steering wheel rotation.
The Premier Auto Trade Sensor range includes Power Steering Switches from the world’s leading manufacturers, covering almost 3 million vehicle applications in Australia and NZ.
When you supply and fit products from Premier Auto Trade you can expect a product designed and tested to the vehicle manufacturer’s specifications offering OE form, fit and function. Premier Auto Trade distributes products throughout Australia via a network of specialised resellers and leading automotive groups.
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