Code
P0550
HUMMER
P — Powertrain
Power Steering Pressure (PSP) Switch Circuit
AI status
Completed
Completed
100%
Causes
- Faulty power steering pressure (PSP) switch
- Open, shorted, corroded or damaged wiring in PSP switch circuit
- Poor connector connection (corrosion, bent pins, contamination)
- Blown fuse or lost power/ground to the switch circuit
- Low power steering fluid or failing power steering pump causing abnormal pressure behavior
- Intermittent contact due to vibration or damaged harness
Symptoms
- MIL/Check Engine lamp illuminated
- Steering effort may be heavier or steering assist reduced (on hydraulic/electro-hydraulic systems)
- Engine idle irregularity or higher idle rpm during steering events (PCM may adjust idle)
- Stored related DTC(s) and possibly reduced vehicle drivability modes
- Intermittent warning or loss of features that rely on pressure feedback
What to check
- Retrieve freeze frame and complete scan tool data; note conditions when code set (engine temp, rpm, steering load)
- Inspect PSP switch connector and wiring for damage, corrosion, pin push-out, or water intrusion
- Check applicable fuses and power/ground circuits for the PSP switch
- Back-probe the switch connector and observe signal with key ON and while engine is running and steering turned (or with steering load applied)
- Check power steering fluid level and visually inspect pump and belt condition
- Perform continuity and resistance checks of wiring between switch and PCM
Signal parameters
- PSP switch is typically a binary (switch) circuit: expected to change state between open and closed as pressure crosses a threshold
- Common reference levels: signal will normally toggle between near 0V (ground) and a reference/battery-related voltage (often ~5V or battery voltage depending on vehicle design) — verify exact expected voltages in vehicle service data
- On a healthy circuit the signal should change state when engine is started/steering load applied; no-change indicates open/short/intermittent
Diagnostic algorithm
- Connect a scan tool, read freeze frame and pending/confirmed codes; note when fault occurred and related data. 2) Visually inspect PSP switch, connector, and harness for damage, corrosion, or contamination. 3) Verify fuses and measure supply voltage and ground at the switch connector with key ON; compare to specifications. 4) Back-probe the switch signal terminal and monitor voltage while an assistant turns the steering or you apply steering load; observe for a clean state change. 5) Check continuity and resistance of wiring from switch connector to PCM harness connector with harness disconnected; repair any opens/shorts. 6) If wiring/power/ground check good, bench-test or replace the PSP switch and re-test. 7) If problem persists after switch replacement, perform PCM connector checks and consider PCM diagnosis or replacement per manufacturer procedures. 8) Clear codes and road test under the conditions that previously set the code to confirm repair.
- similar_codes([
Likely causes
- Failed PSP switch
- Damaged/shorted wiring or poor connector at the PSP switch
- Lost power or ground to the switch (fuse, fusible link, harness)
- Low fluid or weak pump causing unusual pressure switching behavior
Fault status
Status
P0550 — Power Steering Pressure Switch Circuit: PCM detected open/short/intermittent condition in PSP switch circuit. Check switch, wiring, connectors, power/ground and fluid/pump operation.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Repair manuals
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138
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