Air Suspension Disable Switch Circuit Malfunction
The C1840 code indicates a fault in the air suspension disable switch circuit. This switch allows the driver to manually deactivate the air suspension system. The suspension control module detects an abnormal condition in the switch circuit, such as an out-of-range signal, short circuit, or open circuit. The system uses this switch to determine whether to allow normal air suspension operation or maintain a firm suspension mode.
1. Commonly Affected Makes
2. Most Common Causes
- Damaged or corroded wiring in the switch circuit
- Loose, wet, or corroded switch connector
- Short to ground or voltage in the switch circuit
- Failed suspension control module (VRCM or equivalent)
- Excessive resistance in circuit connections
3. Symptoms You Will Notice
- Air suspension warning light illuminated
- Suspension stuck in firm or ride-height mode
- Inability to disable air suspension manually
4. Step-by-Step Diagnosis
Scan for codes and verify C1840 is present
Inspect the air suspension disable switch and connector for damage, corrosion, or looseness
Test the switch circuit for shorts, opens, or excessive resistance using a multimeter
Check for voltage and ground at the switch connector per manufacturer specs
If wiring and switch are good, test the suspension control module
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, but the suspension may remain in a firm or fixed ride height, affecting comfort and handling. Have it diagnosed soon to avoid further issues.
How much does it cost to fix?▼
Typically $100-$300 for switch replacement, or $200-$600 if wiring repair or module replacement is needed.