Error Code P0551 is defined as Power Steering Pressure Sensor Circuit Range/Performance, meaning its performance has been compromised or malfunctioning. This error code is a generic trouble code, meaning it applies to all vehicles equipped with the power steering pressure system. This includes vehicles from but not limited to, Chrysler, Dodge, Infiniti, Jeep, Kia, Lexus, Mazda, Nissan, Toyota, etc. As with other generic codes, specifications on the definition, troubleshooting, and repairs for this, vary from one make and model to another.

Before electric and hydraulic-assisted steering wheels were invented, vehicle manufacturers use unassisted rack and pinion steering system. This made steering your vehicles difficult and inefficient, especially at low speed. Thus, the power steering system was invented.

Generally, a hydraulic-assisted system includes a belt driven power steering pump, box, and various hoses/lines or steering rack, and sensors. The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) which acts as the central computer of the vehicle, works alongside with the power steering pressure (PSP) sensor to oversee the pressure within the system and adjust as needed.

Error code P0551 is set when the PCM determines one or more conditions outside of specific desired range within the PSP sensor circuit. This means the PCM was not able to receive the right voltage input signal from the PSP sensor. In many cases, this takes place at lower vehicle speed. Some vehicles may need to have multiple failure cycles for this code to take place. After the first failure, however, the code should be automatically stored on the vehicle’s onboard computer.

In most cases, this code is a result of an electrical problem. But there are times it could be caused by mechanical issue as well.

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Other related error codes include:

  • P0550
  • P0552
  • P0553
  • P0554

Common Symptoms

  • Erratic idle
  • Stalling when driving at low speed
  • Poor handling, vehicle hard to steer or choppy turning (the result of intermittent assist when steering)
  • Steering fluid leak
  • Whining noises
  • Increase in fuel consumption

Possible Causes

  • Defective PSP sensor
  • Loose or damaged PSP sensor connectors
  • Damage, short, or open in the PSP sensor wiring
  • Bad or incorrect power steering fluid
  • Defective fuse/relay
  • A leak of power steering fluid
  • Defective power steering pump
  • Failed rack or pinion
  • Defective PCM (rare)

How to Check

Before making any diagnosis, make sure you verify and record the integrity of the battery and charging system.

First Step

First thing’s first, check the steering fluid level, add when necessary.

Next, check the parking space for any signs of leaks. If there’s any, check further. If the fluid is low, then make sure you check any mechanical leaks before you proceed on with the electronics.

Check the sensor itself, as fluid can leak to the sensor. Make sure the sensor is dry and has no signs of damage, especially leaks.

Note: This system uses high pressure that could potentially be harmful. Pinhole leaks can be really dangerous. If you’re not familiar with the hydraulic system, then you’ll be better off bringing your vehicle to a reputable repair shop.

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Second Step

Test the sensor. Refer to your vehicle service manual for the specifications. The sensor is usually mounted to the power steering pressure line, with hard aluminum or braided rubber lines and accessible under the hood.

Common leaks are found where the rubber meets the hard pressure line, making it difficult to spot the leak.

Third Step

Find the electrical connector of the pressure sensor. Check for oil residues or soaking signs. If the connector is soaked with oil, then you have a major leak problem. Make sure you clean the oil before reconnecting. A connector showing signs of melting and corrosion must be fixed.

Note: Disconnect the battery before performing any electrical repairs.

Fourth Step

Look for signs of physical damage. Usually, for this code, the sensor is exposed to harsh conditions. If the lines are correctly fastened, then the sensor must be rubbing on something, which over time could cause an electrical problem of some sort. Make sure to fasten those lines, especially the line with the sensor mounted to it.

Fifth Step

You can verify the integrity of the PSP sensor circuit(s). To rule out any problem with your wiring harness, you can disconnect the circuit at the sensor and the PCM. Refer to your vehicle service manual and use your multimeter to verify the right values.

If everything seems to be in good shape up to this point, and the code still persists, then it’s highly recommended that you take your vehicle to your dealer or a reputable repair facility for further advanced and more thorough diagnosis.

How to Fix

Depending on the diagnosis, common repairs for this code include:

  • Replacement of PSP sensor
  • Repair or replacement of open, shorted, or corroded wirings, circuits, or connectors
  • Replacement of dirty power steering fluid
  • Repair of power steering pump leaks
  • Replacement of pump or rack

The risks of stalling while driving is a serious problem associated with this code. This could present safety hazards and inconvenience. Those who are not experienced in manual steering will also have a hard time driving vehicle with this error code.

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