What Does P0551 Code Mean?

OBD-II Code P0551 is defined as a Power Steering Pressure Senor Circuit Range/Performance

The purpose of the Power Steering Pressure Sensor is to alert the PCM that the engine idle speed needs to to be held at a specified level while the driver is operating the Power Steering System at slow vehicle speeds. This is because high levels of hydraulic pressure are needed from the Power Steering Pump in order for the Power Steering system to steer the vehicle at slow speeds. Creating this pressure puts additional load on the engine and commonly occurs when parking the vehicle. 

When the code P0551 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is not seeing the specified electrical change from the Power Steering Pressure Sensor when ever the Steering Angle Sensor shows angle change at slow speeds.

P0551 Symptoms

  • Check Engine Light may illuminate
  • Vehicle may die while turning the steering wheel at slow speeds
  • Vehicle may leak power steering fluid
  • Decrease in fuel economy
  • In unusual cases, there are no adverse conditions noticed by the driver
  • In some cases, there may be performance problems

Common Problems That Trigger the P0551 Code

  • Defective Power Steering Pressure Sensor
  • Defective Power Steering Pressure Sensor wiring or connector
  • Power Steering System Malfunction
  • Dirty Power Steering Fluid

Common Misdiagnoses

  • Engine Idle Air Control Motor
  • Power Steering System

Polluting Gases Expelled

  • HCs (Hydrocarbons): Unburned droplets of raw fuel that smell, affect breathing, and contribute to smog
  • CO (Carbon Monoxide): Partially burned fuel that is an odorless and deadly poisonous gas
  • NOX (Oxides of Nitrogen): One of the two ingredients that, when exposed to sunlight, cause smog

P0551 Diagnostic Theory for Shops and Technicians

When diagnosing a P0551 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive at the freeze frame road speed. Start out from a dead stop watch the Power Steering Pressure Sensor scan data to see if the PCM is receiving the correct input from the Pressure Sensor when the Steering Wheel is turned from lock to lock at very slow speeds or when the vehicle is stopped. If there is no signal from the Pressure Sensor then you may have verified the problem and should perform some pinpoint tests. ALWAYS check the condition of the fluid. Is it brown and dirty or is it clean?


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