Chassis, generic

C0840 Air Suspension Solenoid Valve Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0840 is not documented anywhere in public; no list, bulletin or manual of any carmaker uses it. The title concerns the electrical side of the valves that route air in a self-levelling suspension. Some systems carry one switching valve per air spring in a central block next to the compressor, as in a Continental patent that also places fast lowering valves there; older Ford and Lincoln designs put a two-position vent solenoid on top of each spring, opened by the vehicle dynamics module to fill or vent. A circuit fault means the module sees an open, a short or wrong current on a coil. Bentley logs such a case as C11C613, an open circuit at the rapid filling valve of the Bentayga, and checks the connector first. The affected corner can no longer be raised or lowered.

Likely causes

Water or corrosion in the valve connector (Bentley 2064579/1 checks the plug first)
Open or shorted valve coil, often after moisture got into the system
Chafed harness at the valve block or air spring

Symptoms

  • Air suspension warning or service message
  • One corner sags or ride height cannot be changed

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–900
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

air suspension valveair suspension modulesensor wiring

Related codes

C0810C0815C0820C0821C0822C0823

References: static.nhtsa.gov, motor.com, image-ppubs.uspto.gov, static.nhtsa.gov.