C1930

What Does Code C1930 Mean?

Diagnostic Trouble Code C1930 indicates that the vehicle’s Air Suspension Control Module (ASCM), or in some integrated systems, the Powertrain Control Module (PCM), has detected an “open circuit” condition within the electrical pathway controlling the front air suspension compressor relay. An open circuit signifies a break or interruption in the electrical continuity, preventing current flow through the specified circuit. When the ASCM commands the front air suspension compressor to activate (to inflate the air springs and adjust ride height), it energizes a relay. The ASCM continuously monitors the voltage and current flow through the relay’s control and power circuits. If the module detects an unexpected high resistance or an absence of current flow when the relay should be energized, it interprets this as an open circuit. This prevents the relay from closing its contacts, consequently inhibiting power delivery to the front air suspension compressor. The direct implication is the inability of the air suspension system to properly inflate or deflate the front air springs, leading to compromised ride height control and stability.

Common Symptoms

• Vehicle front end sitting significantly lower or higher than normal (sagging or stiff ride).
• Illumination of a “Service Air Suspension,” “Air Suspension Fault,” or similar warning message on the instrument cluster.
• The air suspension compressor fails to run or produce air pressure when commanded.
• Noticeable degradation in ride comfort, often feeling excessively bouncy or harsh.
• The vehicle may be stuck in a ‘limp home’ mode for the suspension, preventing height adjustments.

What Causes the Code C1930?

• Faulty Front Air Suspension Compressor Relay: The relay itself may have an internal open circuit in its coil windings (control side) or its high-current contacts (power side), preventing it from energizing or passing power to the compressor.
• Damaged or Corroded Wiring: An open circuit can exist in the wiring harness connecting the ASCM to the compressor relay, or from the relay to the compressor motor. This damage can be due to chafing against chassis components, rodent damage, internal wire breakage, or severe corrosion within the wire strands or insulation.
• Corroded or Loose Connector Pins: Poor electrical contact at the relay socket or the wiring harness connectors leading to/from the relay. This is often caused by moisture ingress, oxidation, or improper pin tension/seating.
• Blown Fuse: A blown fuse in the power supply circuit to the compressor relay or the compressor motor itself will present as an open circuit, interrupting current flow. While the fuse protects against overcurrent, its failure results in an open condition.
• Faulty Air Suspension Control Module (ASCM): In less common instances, the internal driver circuit within the ASCM responsible for providing the necessary ground or power signal to energize the relay coil may be defective, leading to an inability to command the relay.

How to Diagnose and Troubleshoot

Diagnosing Code C1930 requires a methodical approach, utilizing a digital multimeter (DMM) and an advanced OBD-II scanner with bi-directional control capabilities.

1. Initial Visual Inspection: Begin with a comprehensive visual inspection of the entire front air suspension system, including the compressor, its relay, and all associated wiring harnesses and connectors. Look for obvious signs of physical damage, chafing, corrosion, or loose connections. Pay particular attention to the relay socket for evidence of burnt terminals or corrosion.
2. Verify Fuse Integrity: Locate the fuse(s) for the air suspension compressor and the relay’s control circuit. Using a DMM, check for continuity across each fuse, or test for battery voltage on both sides of each fuse with the ignition in the ON position. Replace any blown fuses, but be aware that a blown fuse often indicates an underlying short circuit that must be identified and rectified.
3. Relay Circuit Testing:
   • Wiring Diagram Analysis: Obtain a detailed wiring diagram for the vehicle’s air suspension system to accurately identify the compressor relay’s terminals (e.g., coil terminals 85 and 86, power input 30, power output 87).
   • Test Relay Coil Power: With the ignition ON, measure for battery voltage (typically 12V) at one of the relay coil terminals (e.g., 85) in the relay socket. This voltage usually comes from a fused ignition source or directly from the ASCM.
   • Test Relay Coil Ground (Control Signal): Using an OBD-II scanner’s bi-directional controls, command the front air suspension compressor to activate. While commanded ON, measure for a proper ground signal (voltage near 0V) at the other relay coil terminal (e.g., 86). This ground signal is typically provided by the ASCM. If voltage is present at 85 but no ground at 86 when commanded ON, suspect a faulty ASCM driver or an open in the ground control wire.
   • Relay Coil Resistance Check: With the relay removed from its socket, use the DMM to measure the resistance across the relay coil terminals (85 and 86). An acceptable reading is typically between 70-150 ohms. An infinite resistance reading confirms an internal open circuit within the relay coil.
   • Power Circuit Voltage Test: In the relay socket, identify the terminal that supplies constant battery voltage (e.g., terminal 30) to the relay’s power contacts. Confirm constant battery voltage here.
   • Output Circuit Continuity/Voltage: If the relay coil tests good, reinstall the relay. With the compressor commanded ON via the scan tool, verify battery voltage at the relay’s power output terminal (e.g., 87) that leads to the compressor. If no voltage is present, and the relay coil is known good, consider bypassing the relay momentarily with a fused jumper wire (use appropriate fuse rating for compressor current) to directly power the compressor for a quick functional check, exercising extreme caution.
4. Compressor Wiring and Component Check: Disconnect the compressor’s electrical connector. Test for continuity in the power wire from the relay output terminal (e.g., 87) to the compressor connector. Also, verify proper continuity to chassis ground for the compressor’s ground wire. Measure the resistance of the compressor motor itself (if applicable, refer to service manual specifications); an open circuit here could also prevent operation and indirectly contribute to the code if the ASCM monitors current draw.
5. ASCM Output Verification: If all wiring, fuses, and the relay itself test good, and the ASCM is not providing the correct control signal to the relay coil, further diagnosis of the ASCM’s internal driver circuit or its power/ground supply may be necessary.

Recommended Repairs and Solutions

Based on the thorough diagnostic steps, the following repairs are typically recommended:

• Replace the Front Air Suspension Compressor Relay: This is often the most common culprit. If the relay failed internal resistance checks or functional tests, replace it with a new OEM or high-quality aftermarket equivalent part.
• Repair or Replace Damaged Wiring Harness: If diagnostic tests reveal an open circuit in the wiring between the ASCM, relay, or compressor, perform precise wiring repairs. Utilize appropriate gauge wire, high-quality crimp connectors, soldering techniques (where appropriate), and heat-shrink tubing for durability and moisture protection. For extensive or inaccessible damage, replacing the affected section of the wiring harness may be necessary.
• Clean and Secure Electrical Connectors: Address any corrosion or poor pin tension found at the relay socket or other connectors in the circuit. Use electrical contact cleaner and a small pick or brush to clean terminals. Ensure all connectors are securely seated and their locking tabs engaged. Pin re-tensioning tools can be used for loose terminals.
• Replace Blown Fuses and Identify Root Cause: While simply replacing a blown fuse restores power, it is imperative to identify and rectify the underlying cause (e.g., a short circuit in the compressor motor, wiring, or a related component) to prevent the new fuse from blowing immediately.
• Replace Air Suspension Control Module (ASCM): This repair should only be considered as a last resort, after meticulously confirming that the relay, all wiring, fuses, and the compressor itself are in perfect working order, and definitive proof indicates an internal fault within the ASCM’s relay driver circuit. Module replacement often requires specialized programming or calibration.

After any repair, clear the C1930 Diagnostic Trouble Code using an OBD-II scanner. Perform a functional test of the air suspension system, verifying proper compressor operation, accurate ride height adjustment, and ensuring that the code does not return during subsequent driving cycles.