FAQ
TL;DR: 0 errors after repairing the relief‑valve harness on pins 14/44—"The car got zero errors." If your W220 raises but won’t lower with no codes, check wiring from the Airmatic module to the compressor valve first. [Elektroda, viper1989, post #17419643]
Why it matters: It helps W220 owners fix "won’t lower" Airmatic issues without wasting money on unnecessary parts.
Quick Facts
- Height sensor signal target: Typical 2.0–3.0 V via SD; out‑of‑range blocks calibration. [Elektroda, viper1989, post #17172283]
- A healthy compressor can show ~14.4 bar yet the car still may not lower; pressure ≠ venting. [Elektroda, viper1989, post #17172283]
- Access the valve block by removing the wheel‑arch liner; bumper removal not required. [Elektroda, mario 77, #17174028]
- Valves ticking but no drop points to a bleed/relief valve or valve‑block path issue. [Elektroda, mario 77, #17187988]
- Case‑proven fix: repair broken wires between Airmatic pins 14 and 44 and the relief valve. [Elektroda, viper1989, post #17419643]
Why does my Mercedes W220 Airmatic raise but won’t lower, with no errors?
If both front and rear ignore SD lowering, suspect the compressor relief (bleed) valve or the valve block. Check height sensor signals next. "Generally, if it stands too high, it should be a height sensor, a bleed valve or a valve bar." [Elektroda, mario 77, #17187988]
How do I test the compressor relief (bleed) valve on a W220?
Power the solenoid directly to confirm it actuates. "You can give him power and control the ground." For a flow check, loosen the pipe on the valve block that isn’t in line with the others, then command a lower in SD and see if it vents. [Elektroda, mario 77, #17189093]
What are normal Airmatic height sensor voltages on the W220?
Star Diagnosis targets about 2.0–3.0 V per sensor. The case showed 1.48 V and 0.48 V on two sensors, which blocked calibration. Bring each sensor into range before attempting calibration. [Elektroda, viper1989, post #17172283]
Can a valve block click and still not lower the car?
Yes. Clicking only proves the coil energizes, not that air flows. If it clicks and the bellows won’t drop, suspect a stuck spool or blocked vent path in the block or compressor relief valve. [Elektroda, andrzej20001, post #17176973]
Do failed Airmatic valves always click when actuated?
No. "These valves just get blurred so they don't even click." Silence can indicate a seized spool or an open‑circuit coil. Replace or rebuild as needed. [Elektroda, daw2, post #17176982]
Where is the W220 Airmatic valve block and how do I access it?
It’s accessible through the wheel‑arch area. Remove the wheel‑arch liner to reach it. "Just remove the wheel arch." Bumper removal is unnecessary for service. [Elektroda, mario 77, #17174028]
My valve block was replaced, but it still won’t lower. What next?
Stop chasing parts. In this case, replacing the valve block and module changed nothing. Focus on the compressor relief valve and wiring continuity to it from the Airmatic control module. [Elektroda, viper1989, post #17185692]
How do I check for wiring faults to the relief valve?
Measure continuity from the Airmatic module to the valve while flexing the harness. "According to the diagram, the connection… is pins 14 and 44." Repair broken sections; this resolved the issue and cleared all errors in the case. [Elektroda, viper1989, post #17419643]
Quick 3‑step: how do I diagnose a W220 that won’t lower?
- Command lowering with SD and listen if front and rear valves actuate.
- Loosen the non‑inline pipe on the valve block and try to lower.
- If still high, suspect the height sensor, bleed (relief) valve, or valve block. [Elektroda, mario 77, #17187988]
Does a strong compressor guarantee the car will lower?
No. One case showed ~14.4 bar compressor pressure and still no lowering. Lowering requires the vent path to open via the relief/bleed control, independent of stored pressure. [Elektroda, viper1989, post #17172283]
Is adding weight to the trunk a safe way to force calibration?
Avoid it. The owner added about 200 kg to bring sensor voltages into range, but calibration stored wrong parameters and risked the bellows. Fix signals and venting first, then calibrate. [Elektroda, viper1989, post #17173926]
I measure 0–9 V at the relief‑valve connector. What does that suggest?
Intermittent or low voltage at the valve points to a harness or control issue. Investigate the loom and connector integrity before condemning the module or compressor. [Elektroda, viper1989, post #17206325]
Should I check the Airmatic control module for corrosion?
Yes. Inspect the controller and plug for corrosion (“greenery”). Clean contacts and verify the connector seals before deeper parts replacement. Corrosion can block control signals. [Elektroda, fructon, post #17172583]
What tools should I use to test the harness and valve control?
Use a test lamp/bulb to load‑test the harness and check output directly at the controller. Typical relief valves are 12 V solenoids; confirm supply and ground under command before blaming the module. "I always leave the driver at the end." [Elektroda, nicram1941, post #17216564]
