Air Suspension Compressor Relay Circuit Short to Battery
Code C1931 indicates that the Air Suspension Control Module (VSM/SCM) has detected a short to battery voltage (B+) in the control circuit of the front compressor relay. This occurs when the module commands the relay off (low output) but still reads battery voltage on the drive circuit, preventing proper compressor control and disabling the leveling system.
1. Commonly Affected Makes
2. Most Common Causes
- Compressor relay with stuck or internally shorted contacts
- Control circuit wiring (between module and relay coil) shorted to battery voltage
- Failed output driver inside the suspension control module (VSM/SCM)
- Corroded or bent connector pins bridging power and control circuits
3. Symptoms You Will Notice
- Air suspension inoperative or stuck at one height
- Compressor runs continuously or not at all
- Warning light on dash (e.g., 'Suspension Fault')
4. Step-by-Step Diagnosis
Scan for codes and verify C1931 is present
Inspect relay and control circuit for shorts to B+ using a multimeter
Check connector pins for corrosion or damage
Test relay operation and replace if stuck
If wiring and relay are good, suspect a failed suspension control module
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is possible but not recommended for long distances. The suspension may not self-level, causing poor handling and increased wear. Have it diagnosed promptly.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on whether the issue is a simple relay replacement or a more expensive control module.