1) Quick system theory (why it works)
- Components: air compressor (creates pressure), dryer/reservoir/check valve (stores pressure, removes moisture), air lines/fittings (carry air), air springs/struts (suspension volume), height/level sensors (measure ride height), valve block/solenoids (direct air in/out), control unit/relays/pressure switch (control logic and cut‑out).
- Function: compressor pressurizes the reservoir; the valve block sends air to a specific spring to raise a corner and vents it to lower. Height sensors tell the controller when to add or dump air. The dryer prevents moisture and debris from damaging valves and compressor.
- Fault modes: leaking air springs/lines => sagging corner and continuous compressor running; failed compressor/dryer => no pressure or contaminated air; stuck/failed solenoid block => a corner won’t hold pressure or won’t inflate; bad height sensor/ECU wiring => incorrect or no leveling commands.

2) Ordered diagnostic/repair workflow (theory + how each repair fixes the fault)
1. Symptom triage and safety
- What to do: Observe which corners sag, when the compressor runs, check for dashboard warnings. Support vehicle on stands and relieve system pressure before disassembly.
- Why: Confirms failure mode (leak vs. control vs. pressure source) and avoids injury from pressurized components.

2. Visual and auditory inspection
- What to do: With ignition on watch compressor behavior: runs briefly then stops (normal) vs. runs long/continually. Inspect lines, fittings, air springs for cracks, dry rot, oil, or loose clamps. Listen for hissing leaks.
- Why/how it fixes: Locating obvious external leaks or damaged springs points to the least invasive repairs (replace boot/line/spring). Fixing an external leak restores airtightness so the compressor can reach cut‑out and system holds ride height.

3. Scan and electrical checks
- What to do: Read any ECU/air-suspension codes (if available). Check compressor power/ground, relay operation, and solenoid valve block wiring with a multimeter.
- Why/how it fixes: Detects electrical faults that would prevent the compressor or valves from operating. Repairing wiring/relays restores control signals so the system can command air flow correctly.

4. Leak isolation test
- What to do: Pressurize system (use diagnostic mode or allow compressor to run) and spray soapy water on springs, fittings, lines, valve block, and connections. Alternatively use an electronic leak detector. Note any persistent leaks.
- Why/how it fixes: Identifies the exact leak source. Replacing/fitting leaking part restores retention of pressure; the compressor then cycles normally and the corner remains at target height.

5. Repair/replace exterior air leaks (first-line mechanical repairs)
- What to do: Replace leaking air spring/strut assemblies, cracked flexible lines, or failed fittings/O‑rings. Tighten or replace clamps. Use manufacturer‑specified replacement parts and O‑rings/torque.
- Theory of fix: Air springs and lines provide the sealed volume. Replacing damaged components restores the sealed chamber so the valve block can maintain pressure and the height sensors receive a steady mechanical result. This stops continuous compressor running and corrects sag.

6. Check and service valve block/solenoids
- What to do: If a single corner will not hold or never inflates despite good supply pressure, remove and bench‑test the valve block (apply supply pressure and actuate solenoids) or swap with another bank if possible. Replace valve block or rebuild with new diaphragms/filters if solenoids are leaking/sticking.
- Theory of fix: Valve block controls air routing and sealing. A sticking or leaking solenoid allows air to vent or prevents flow to a spring. Replacing or rebuilding restores controlled flow and proper sealing so a corner can be inflated and held.

7. Compressor and dryer service/replacement
- What to do: If compressor fails to build adequate pressure, overheats, draws excessive current, or water/oil contamination is present, replace the compressor and desiccant dryer. Inspect inlet filter and check valve/reservoir.
- Theory of fix: Compressor is the supply source; the dryer protects from moisture that causes internal wear and valve block failure. A new compressor with a dry intake restores required pressure and prevents recurring contamination-related failures.

8. Height sensor and linkage repair
- What to do: If electrical and pneumatic components are good but height readings are wrong, inspect sensor linkages, mounts, and sensor outputs with a multimeter or scan tool. Replace corroded pivots, rebuild linkages, or replace the sensor.
- Theory of fix: Height sensors provide the reference for the control unit. A misreading causes erroneous inflate/deflate commands. Fixing or replacing them restores correct input so the controller maintains intended ride height.

9. Final sealing, routing, and anti‑contamination measures
- What to do: Replace all old O‑rings, use proper lubricants, secure lines away from heat/chafe points, replace clamps, and renew any in‑line filters.
- Theory of fix: Proper sealing and routing prevents new leaks and protects components from failure. Clean dry air and good seals extend component life and ensure stable pressures.

10. Functional test and calibration
- What to do: Repressurize, command the system through its cycles (auto-level or diagnostic mode), check that each corner rises to the correct height and holds. Confirm compressor cycles to cut‑out and does not run continuously. Clear codes and verify no reappearance.
- Why/how it fixes: Verifies that repairs restored closed system integrity, control, and sensor feedback; ensures symptoms are resolved and no hidden faults remain.

3) Quick troubleshooting heuristics (practical theory)
- Continuous compressor run => persistent leak, check springs/lines/fittings first; if none, check check‑valve/reservoir and valve block leaks.
- Single corner sagging => local air spring/line fitting or its solenoid/valve; bench‑test valve block to confirm.
- All corners drop slowly => reservoir leak, check valve, or manifold leak.
- Compressor won’t start but system unpressurized => electrical fault (relay/fuse/ground/sensor), not mechanical.
- Compressor starts but can’t build pressure => worn compressor, clogged dryer/filter, failed intake check valve.

4) Safety and longevity notes (brief)
- Always depressurize before disconnecting air lines. Support vehicle securely. Replace desiccant/dryer whenever replacing compressor. Use OEM or equivalent parts for diaphragms/valves to avoid fitment/pressure problems.

5) Verification of fix (how you know repair worked)
- After repair the system should: reach cut‑out pressure in a reasonable time, maintain ride heights with compressor off, not run continuously, and reproduce correct height sensor feedback. If these are true the root cause (leak, failed valve, bad compressor, or bad sensor) has been addressed.

Done.
rteeqp73

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