Code C0690 on the 2023 Acura MDX indicates a malfunction in the rear left air suspension valve circuit. The MDX Type S and certain other trims feature adaptive air suspension with solenoid valves that control air flow to each air spring.
Air Suspension Valve Function
Solenoid valves in the air suspension system control air flow to individual air springs for inflation and deflation. Each corner has a valve that opens to allow air in (raising that corner) or releases air out (lowering that corner). The rear left valve manages air flow to the rear left air spring.
Warning Signs
With C0690 present, the air suspension warning light activates and a message displays in the Driver Information Interface. The rear left corner may not respond to height adjustment commands - it might stay at one height or slowly drift down. The entire suspension system may enter a protective mode with limited functionality.
Diagnostic Focus
Valve problems can be electrical (coil failure, wiring issues) or mechanical (stuck valve, contamination). Use diagnostic equipment to command the valve open and closed while monitoring system response. Listen for the valve clicking when commanded. Check electrical supply to the valve and test coil resistance against specifications.
Repair Requirements
If the valve has failed, replacement involves accessing the valve block (typically in the trunk area or under the vehicle) and replacing the faulty valve solenoid. Some systems use integrated valve blocks where the entire block may need replacement. After repairs, bleed air from the system and perform initialization procedures.