C1873

What Does Code C1873 Mean?

DTC C1873 indicates an Air Suspension RF Air Spring Solenoid Output Circuit Failure. This diagnostic trouble code signifies that the Air Suspension Control Module (ASCM), also frequently referred to as the Suspension Control Module (SCM) or integrated into a Body Control Module (BCM) or Chassis Control Module (CCM) in modern vehicles, has detected an electrical fault within the control circuit for the Right Front (RF) air spring solenoid. This solenoid is a critical electro-mechanical component responsible for regulating the precise flow of compressed air into and out of the RF air spring bladder, thereby controlling the ride height, stiffness, and overall dynamic damping characteristics of that specific corner of the vehicle.

The ASCM continuously monitors the electrical integrity of this circuit. It detects a failure when electrical parameters such as voltage, resistance, or current fall outside of the manufacturer’s specified operational range. This could manifest as an open circuit (infinite resistance), a short circuit (zero or near-zero resistance), or an excessively high resistance condition in the solenoid coil or its associated wiring. When the ASCM detects such an anomaly, it cannot reliably command the solenoid to actuate, leading to a loss of control over the RF air spring’s air pressure and, consequently, its ride height and damping. The system enters a fault mode, typically illuminating a warning indicator on the instrument cluster.

Common Symptoms

• Incorrect Right Front Ride Height: The most prominent symptom is a visible sag or excessive height at the vehicle’s right front corner, or the inability for that corner to adjust its height.
• Air Suspension Warning Light: Illumination of the “AIR SUSPENSION,” “CHECK SUSPENSION,” “SERVICE SUSPENSION,” or a generic “CHASSIS” warning lamp on the instrument cluster.
• Degraded Ride Quality: Noticeable deterioration in ride comfort, handling, or stability, particularly over bumps or during cornering, due to improper air spring function.
• Excessive Compressor Operation: The air suspension compressor may run continuously or for extended periods attempting to compensate for the inability to control the RF air spring, potentially leading to compressor overheating or failure.
• Uneven Vehicle Stance: The vehicle may appear visibly lopsided, especially when parked, due to the inability of the RF air spring to maintain its programmed height.

What Causes the Code C1873?

• Damaged Wiring Harness: Open circuits, short circuits to ground or power, or excessive resistance in the wiring connecting the Air Suspension Control Module (ASCM) to the RF air spring solenoid. This can be caused by chafing, rodent damage, impact, corrosion, or incorrect repairs.
• Faulty RF Air Spring Solenoid: Internal electrical failure within the solenoid itself, such as an open coil, shorted coil, or excessive resistance in the winding, preventing it from actuating when commanded.
• Corroded or Loose Electrical Connectors: Poor electrical contact at either the solenoid connector or the ASCM connector due to corrosion, bent pins, or insufficient terminal tension.
• Water Intrusion: Water ingress into the solenoid connector, the solenoid housing, or sections of the wiring harness, leading to corrosion and short circuits.
• Air Suspension Control Module (ASCM) Malfunction: While less common, an internal failure within the ASCM’s driver circuit for the RF air spring solenoid can cause this code.

How to Diagnose and Troubleshoot

Diagnosing C1873 requires systematic electrical testing and often a capable scan tool with bidirectional control. Always begin with a complete vehicle scan to identify any other related DTCs that might point to a broader system issue.

1. Visual Inspection:
   • Inspect the wiring harness leading to the RF air spring solenoid and the solenoid connector itself. Look for obvious signs of damage, fraying, cuts, chafing, corrosion, or loose connections.
   • Check the integrity of the air spring bladder for any signs of physical damage or air leaks, although the code is electrical, a failing air spring might have compromised components.
   • Verify proper routing and securement of the wiring away from moving components or heat sources.
2. Scan Tool Diagnostics:
   • Use an advanced OBD-II scan tool capable of communicating with the Air Suspension Control Module (ASCM).
   • Monitor live data parameters related to the RF air spring solenoid, if available (e.g., commanded status, feedback voltage).
   • Attempt to use bidirectional controls to cycle the RF air spring solenoid ON and OFF. Listen for an audible click from the solenoid and observe any changes in vehicle height or parameter readings. If no click is heard or no change observed, further electrical testing is warranted.
3. Electrical Circuit Testing (Ignition OFF, Battery Disconnected for resistance/continuity tests):
   • Solenoid Resistance Test: Disconnect the RF air spring solenoid connector. Using a Digital Multimeter (DMM) set to ohms, measure the resistance across the two terminals of the solenoid itself. Compare this reading to manufacturer specifications (typically a low resistance, e.g., 2-10 ohms). An open circuit (OL or infinite resistance) indicates a faulty solenoid coil. A reading close to 0 ohms indicates a shorted solenoid.
   • Wiring Continuity Test: Disconnect both the ASCM connector and the RF air spring solenoid connector. Using a DMM, check for continuity (low resistance, typically < 5 ohms) between the corresponding terminals of the ASCM and solenoid connectors for both the control and return wires. An open circuit indicates a break in the wiring.
   • Short to Ground/Power Test: With both connectors disconnected, check for shorts to ground by measuring resistance between each wire in the solenoid circuit and a known good chassis ground. Check for shorts to power by checking resistance between each wire and a fused battery positive terminal. Both readings should be infinite (OL).
4. Voltage and Ground Verification (Ignition ON):
   • Reconnect the ASCM connector. With the solenoid connector still disconnected and the ignition ON, carefully back-probe the solenoid connector to check for power and ground signals when the solenoid is commanded ON by the ASCM (using bidirectional control or by specific system conditions). Verify adequate voltage (near battery voltage) at the power feed and a solid ground. Significant voltage drops indicate high resistance in the circuit.

Recommended Repairs and Solutions

• Repair or Replace Wiring and Connectors: If diagnostic steps identify damage to the wiring harness or connectors (chafing, corrosion, breaks), the affected section must be repaired or replaced. Use appropriate automotive-grade wire, heat-shrink tubing, and crimp connectors for durable, weatherproof repairs. If corrosion is minor, clean the terminals with electrical contact cleaner and apply dielectric grease.
• Replace RF Air Spring Solenoid: If the solenoid tests faulty (open, shorted, or incorrect resistance), it must be replaced. In many applications, this solenoid is an integral part of the air spring assembly itself, necessitating replacement of the entire air spring unit. Ensure proper torque specifications are used for mounting hardware and O-rings are correctly seated.
• Air Suspension Control Module (ASCM) Replacement: Only consider ASCM replacement after thoroughly ruling out all external wiring and solenoid issues. If the ASCM is diagnosed as faulty, it will typically require programming or calibration with a factory-level scan tool after installation to ensure proper system function.
• Post-Repair Procedures: After any repair, clear all diagnostic trouble codes using a scan tool. Perform a system function test by cycling the ignition, running the engine, and potentially commanding ride height adjustments with the scan tool. Verify that the system operates correctly and that no warning lights return. A complete air suspension system calibration may be necessary after component replacement.