Buying a W220 S-Class.

Inspect in daylight and on a lift. Rust starts at the wheel-arch lips, door bottoms and trunk lid, then matters more at the sills, jacking points, floors and suspension mounting areas. Look behind liners and plastic trim, not merely at polished outer paint. Facelift cars tend to fare better, but none is exempt; bubbling around a trim edge is the start of a repair, not patina.

Every W220 has AIRMATIC unless its data card shows option 487, Active Body Control. View the car cold after it has stood overnight: all four corners should be level. Raise and lower it from the switch, watch the time it takes, listen for a compressor that keeps running and take every “car too low” message seriously. A leaking strut can destroy an otherwise healthy compressor.

ABC is hydraulic, not air suspension. It controls roll brilliantly and costs accordingly: inspect the lines and struts for dampness, the reservoir fluid for neglect, and the tandem pump for noise or weak pressure. Red warnings, bouncing at idle or a corner that sinks are reasons for a specialist diagnosis, not for accepting a seller's promise of a sensor.

Press deeply into the front passenger carpet and inspect beneath it; the thick foam can hide liters while the surface feels dry. Debris blocks the reed valve in the fresh-air plenum, water overflows into the cabin and travels along the floor wiring toward control modules. Mercedes issued bulletin P-B-83.10/75 for a secondary drain after the problem became the subject of a US settlement.

Look for tide marks, musty odor and green corrosion at connectors, then inspect the trunk wells and electronics bays. A clear drain is good; invoices for the approved modification and any properly repaired water damage are better. Random warning messages on a damp car are connected evidence, not separate minor faults.

On M112 and M113 cars, insist on a cold start and inspect the rear of the heads for oil from cam plugs and breather covers. On early M113 cars, watch the bonded crank pulley run true and verify the relevant harmonic-balancer campaign by VIN. Misfires can mean ignition rather than internal damage, but there are twelve spark plugs in a V6 and sixteen in a V8. Supercharged S 55s add intercooler pumps, belts and heat to the checklist.

An S 600 needs a model-specific inspection: oil from the buried cooler and breather assembly on the M137; coil cassettes, voltage transformers, turbo plumbing and mounts on the M275. On diesels, lift the cover and look for tar around injector seats, then check boost, EGR and cold starting. The OM628 V8 CDI belongs with a workshop that already knows it.

Most cars use the 722.6 five-speed; its conductor plate can fail and the 13-pin connector sleeve can leak fluid that wicks toward the control module. From September 2003, rear-drive S 430 and S 500 models gained the 722.9 seven-speed. Both should shift cleanly cold and hot, with records for fluid and filter changes — “sealed for life” is not a maintenance history.

Test every switch because one pneumatic or electronic fault can disable several luxuries at once: soft-close on all four doors and the trunk, every seat direction and memory, heating, ventilation and massage, rear blind, sunroof, mirrors, windows, climate control, COMAND, DISTRONIC and Keyless-Go. Facelift does not identify the audio network: D2B changed to MOST on 1 September 2003. Repeated hissing or a PSE pump that times out points to a leak, not character.

A generic OBD reader sees only a fraction of this car. Have a Mercedes specialist scan every control unit with STAR/DAS, distinguish stored faults from current ones, and verify that warning lamps have not simply been suppressed. Favor invoices for drains, suspension, transmission service and electrical diagnosis over a stamped book alone; confirm the VIN, wheelbase, suspension and 4MATIC specification match the car, then check completion of the applicable ABC, instrument-cluster and harmonic-balancer campaigns.