Technical Description of OBD-II Trouble Code
The circuit range/performance of the power steering pressure sensor
What does that signify?
This generic DTC is applicable to all OBD-II vehicles that have a power steering pressure sensor, including vehicles from Infiniti, Nissan, Toyota, Lexus, Mazda, Dodge, Chrysler, Jeep, Kia, etc.
Before the invention of hydraulically and electrically assisted steering systems, manufacturers used unassisted rack and pinion steering systems. This made steering at low speeds extremely difficult and inefficient.
For this reason, the power steering system was invented. Generally, a hydraulically assisted system includes a belt-driven power steering pump, steering rack/box, and various hoses/lines and sensors. The Engine Control Module (ECM) or Powertrain Control Module (PCM) works together with the power steering pressure sensor to monitor the pressure within the system and make adjustments accordingly.
The ECM illuminates the check engine light with the code P0551 and associated codes when it detects a condition outside the desired range within the circuit of the power steering pressure sensor. Most of the time, this code is triggered by an electrical issue, but mechanical problems could also be the cause.
The P0551 Power Steering Pressure Sensor Circuit Range/Performance code is set when the ECM/PCM detects a condition outside specific parameters within the sensor’s circuit. It is one of five related codes, which are P0550, P0551, P0552, P0553, and P0554.
What is the severity of this DTC?
Given the fact that it is possible for the power steering system to completely fail and still be able to drive the car, the severity of this issue is considered low. However, it is important to note that leaving any issue unresolved for a long time can result in higher costs in the long run.
An example of a power steering fluid pressure switch/sensor:
What are some of the symptoms of the code?
Symptoms of a P0551 diagnostic code may include:
What are some of the common causes of the code?
Causes for this code may include:
What are some P0551 troubleshooting steps?
Make sure to check for technical service bulletins (TSBs) for your vehicle. Accessing a known fix can save time and money during diagnosis.
Tools
Some of the things you may need when diagnosing or repairing the power steering circuits and systems:
Safety Tips
NOTE: ALWAYS verify and record the integrity of your battery and charging system before further troubleshooting.
Basic Step #1
Always start with the simplest steps. Check the power steering fluid level and top up if necessary. Check your parking space for any signs of a leak. If there is a fluid leak, further investigation is required. If the fluid level is low, it is important to repair any mechanical leaks before proceeding with electrical diagnosis. Inspect the sensor itself for any signs of leakage or damage.
NOTE: These systems operate at high pressures, which can be dangerous. Pinhole leaks are hazardous. If you are not familiar with the dangers of working with hydraulic systems, it is recommended to take your vehicle to a reputable repair facility.
Basic Step #2
To determine if the sensor is the issue, it needs to be tested. Refer to your service manual for the required specifications. The sensor is usually mounted to a power steering pressure line, which can be accessed from under the hood.
NOTE: A common leak occurs where the rubber meets the hard pressure line. Sometimes, the rubber separates, causing a difficult-to-find leak.
Basic Tip #3
Inspect the electrical connector on the pressure sensor for any oil residue. If the connector is soaked in oil, the leak needs to be addressed and the oil must be cleaned before reconnecting. If the connector shows signs of melting or corrosion, it must be repaired.
NOTE: Always disconnect the battery before performing any electrical repairs.
Basic Step #4
Check for physical damage. In this case, the sensor is exposed to harsh conditions. If the lines are not properly fastened, the sensor may rub against something and eventually cause an electrical problem. Secure any loose lines, especially the one with the mounted sensor.
Basic Step #5
You may be able to verify the integrity of the power steering pressure sensor circuit(s). To rule out any issues with the wiring harness, disconnect the circuit at the sensor and the ECM. Use a multimeter and refer to your service manual to ensure that all the desired values are within the correct range. If everything appears to be fine up to this point, it is recommended to take the vehicle to a reputable repair facility.
