This code indicates the power steering pressure sensor (or switch) is sending a voltage signal to the PCM that falls outside the expected range or behaves irrationally for the given engine load conditions. The PCM uses this input to raise idle speed when high steering effort is detected; a range/performance fault means the circuit data cannot be trusted.
The internal pressure transducer or switch contacts degrade internally, producing voltage readings that drift above or below the calibrated threshold regardless of actual hydraulic pressure.
Corroded, oil-contaminated, or bent pins at the sensor harness, along with chafed or shorted wires between the sensor and PCM, disrupt signal integrity and reference voltage.
Low fluid level, air ingestion, or a restricted supply hose causes erratic pressure spikes or drops that the sensor reports as irrational circuit performance.
An open or high-resistance condition in the 5-volt reference line from the PCM to the sensor results in out-of-range sensor output even when the sensor itself is functional.
Internal signal processing faults within the PCM are statistically rare for this code and should only be considered after the sensor, wiring, and hydraulic system have been verified.
Short trips are generally manageable, but the engine may stall during parking lot maneuvers when steering load is highest, creating a potential safety hazard.
No; the fault is electrical and affects only the pressure monitoring circuit. Hydraulic assist typically remains functional, though idle quality may degrade when steering.
Almost never. The PCM is rarely the root cause of P0551; accurate diagnosis almost always identifies a faulty sensor, wiring issue, or hydraulic condition.
Clearing the code may extinguish the light temporarily, but if the sensor, wiring, or fluid condition remains defective, the code will reset within a few drive cycles.