P0551

Code

MITSUBISHI P — Powertrain

Power steering pressure switch

Brand: MITSUBISHI

Type: P — Powertrain

Views: UK: 11 EN: 15 RU: 19

AI status

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Page language: EN

Causes

Faulty power steering pressure switch (mechanical/electrical failure)
Damaged, corroded or loose connector at the switch
Open, short to ground or short to power in the harness between switch and PCM
Low power steering fluid level or air in the system preventing normal pressure rise
Failed power steering pump or relief valve producing abnormal pressure
Intermittent wiring due to chafing or pinched cable

Symptoms

Malfunction Indicator Lamp (MIL/Check Engine) illuminated
Power steering warning light (on some models) or reduced steering assist at idle
Hard or heavy steering feel, especially at low speeds or idle
Intermittent loss of steering assist or noisy pump/whine from power steering
Possible changes to idle or engine behavior if ECM uses signal for driveability control

What to check

Read and record freeze frame data and stored related codes with a diagnostic scanner
Visually inspect pressure switch connector and wiring for corrosion, damage, loose pins or moisture
Check power steering fluid level and inspect for leaks (hoses, rack, pump)
Back-probe the switch connector with key ON/engine OFF and while engine running to observe signal change as system pressurizes
Listen for pump noise and feel for steering assist change when engine is started
Confirm vehicle battery/charging system voltage is within specification before signal tests

Signal parameters

Signal type: on/off or variable voltage input to PCM depending on design (switch closes or voltage changes when pressure threshold reached)
Typical electrical range: 0–5 V signal expected to PCM (varies by vehicle). Many switches toggle between low (near 0–1 V) and high (near 4–5 V) or provide continuity to ground when pressurized — consult OEM spec for exact values
Continuity: when acting as a simple switch, resistance should be near infinite (open) at low pressure and near 0 Ω (closed) at high pressure; verify with pressure applied
Reference: verify PCM reference voltage (often 5 V) and ground continuity before concluding switch failure

Diagnostic algorithm

Retrieve code(s) and freeze-frame, note operating conditions when fault set (engine temp, rpm, steering load).
Visually inspect pressure switch connector and harness from switch to PCM; repair any damage, corrosion, or poor connections.
Check power steering fluid level and condition; top up if low and inspect for leaks; bleed air if needed. Clear code and retest to see if condition returns.
With key ON (engine OFF) and then with engine running, back-probe the switch signal pin and measure voltage/continuity. Observe change as power steering system pressurizes (have an assistant turn steering lock-to-lock slowly or start engine). Compare to OEM expected behavior.
If signal does not change or is out of range, unplug the switch and check for correct reference voltage and ground at the connector. If reference is missing or shorted, trace/repair wiring to PCM.
If wiring and reference are good, bench-test or replace the switch and confirm correct switching under pressure (or substitute known-good sensor).
If new switch and wiring good but code persists, check PCM input circuit for shorts/opens and consider module testing or reflash as a last resort.
After repair, clear codes and perform road test under conditions that originally set the DTC; confirm the code does not return.

Likely causes

Corroded/loose connector or damaged wiring between the switch and PCM
Failed pressure switch (most common replacement item)
Low fluid level or leak causing abnormal pressure behavior
Faulty power steering pump or internal hydraulic problem

Fault status

⚠️ Status

P0551 — Power Steering Pressure Switch Circuit Range/Performance. The engine control module detected a signal from the power steering pressure switch that is outside expected range or not switching as designed. Inspect switch, wiring, fluid level/pressure and PCM input.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours

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P0551 — Power steering pressure switch