C1874

What Does Code C1874 Mean?

DTC C1874 signifies an Air Suspension RF Air Spring Solenoid Output Circuit Open. This code indicates that the Air Suspension Control Module (ASCM), or a dedicated Suspension Control Module (SCM), has detected an open circuit condition in the electrical pathway leading to the right front (RF) air spring solenoid. The RF air spring solenoid is a critical component within the vehicle’s active air suspension system. Its primary function is to precisely regulate the airflow into and out of the RF air spring, thereby controlling the ride height and damping characteristics for that specific corner of the vehicle. An “open circuit” means that there is a break in the electrical path, preventing current from flowing through the solenoid coil. The ASCM typically monitors the resistance, voltage drop, or current flow within this circuit. When it detects an abnormally high resistance or an absence of current where current should be flowing during a command, it interprets this as an open circuit and sets code C1874. This fault directly impacts the ASCM’s ability to command the RF air spring, often leading to incorrect ride height or compromised ride quality at the right front corner.

Common Symptoms

• The right front corner of the vehicle appears noticeably lower or higher than the other corners.
• A dashboard warning light related to the air suspension system (e.g., “AIR SUSPENSION,” “CHECK SUSPENSION,” or a generic malfunction indicator lamp) illuminates.
• The vehicle exhibits an unbalanced or uneven ride quality, particularly at the front.
• A noticeable harshness or excessive bouncing sensation from the right front wheel.
• Inability to adjust the vehicle’s ride height, either manually or automatically, due to the system fault.
• Audible compressor operation for extended periods, potentially indicating the system is attempting to compensate for an inability to control the RF spring.

What Causes the Code C1874?

• Internal open circuit within the RF air spring solenoid: The solenoid’s coil windings may have failed, broken, or corroded internally, leading to infinite resistance.
• Damaged or compromised wiring harness: The electrical wiring connecting the RF air spring solenoid to the ASCM may have sustained physical damage (e.g., chafing, cuts, breaks), corrosion, or a compromised splice point.
• Corroded, loose, or spread electrical connector pins: The multi-pin connector at the RF air spring solenoid or at the ASCM itself may have poor terminal tension, corrosion, or bent pins, leading to an intermittent or complete open circuit.
• Faulty Air Suspension Control Module (ASCM) output driver: Less common, but an internal failure within the ASCM’s output circuit responsible for driving the RF air spring solenoid could cause this code.
• Blown fuse or open fuse link: While an open circuit often implies downstream of a fuse, a related fuse for the solenoid’s power supply could be blown, resulting in an open circuit condition for the solenoid.

How to Diagnose and Troubleshoot

Accurate diagnosis of C1874 requires a systematic approach using a professional-grade scan tool and a digital multimeter (DMM).

1. Verify the Complaint and Perform Visual Inspection:
   • Confirm the vehicle exhibits the described symptoms, especially regarding ride height.
   • Visually inspect the entire right front air spring assembly, its electrical connector, and the visible sections of the wiring harness leading to it. Look for obvious signs of damage, chafing, corrosion, or rodent damage.
   • Check for any modifications or aftermarket components that could affect the air suspension system.
2. Scan Tool Diagnostics:
   • Connect an OBD-II scan tool and confirm the presence of C1874. Check for any other related or pending DTCs in the ASCM or other chassis modules.
   • Access live data parameters for the air suspension system. Look for parameters such as commanded solenoid states, individual wheel height sensor readings, and air pressure sensor readings. Note any discrepancies or illogical values.
   • If supported, attempt to actuate the RF air spring solenoid via the bi-directional controls on the scan tool. Listen for an audible click from the solenoid or feel for a faint vibration. An absence of response further confirms the open circuit.
3. Digital Multimeter (DMM) Tests (with Ignition OFF and connector disconnected):
   • Solenoid Resistance Test: Disconnect the electrical connector from the RF air spring solenoid. Using the DMM set to ohms (Ω), measure the resistance across the two terminals of the solenoid itself (on the air spring side, not the harness side). A functional solenoid typically has a resistance between 8-15 ohms (consult service information for exact specifications). An “OL” (open loop) or infinitely high resistance reading indicates an internal open circuit within the solenoid.
   • Harness Continuity Test (Control Wire): With the solenoid disconnected, locate the control wire pin for the RF solenoid at the harness connector. With the ASCM connector also disconnected, measure the continuity (Ω) of this wire from the solenoid harness connector back to its corresponding pin at the ASCM harness connector. Resistance should be less than 0.5 ohms. An “OL” or high resistance indicates a break in the wiring.
   • Harness Continuity Test (Power/Ground Wires): Identify the power and ground wires at the solenoid harness connector. Check the power wire for continuity back to its source (e.g., fuse box, ASCM power output) and the ground wire for continuity to a known good chassis ground point (again, less than 0.5 ohms).
   • Voltage Supply Test (Ignition ON, solenoid disconnected): Reconnect the ASCM connector (if disconnected for previous tests) and turn the ignition to the ON position. Use the DMM set to volts DC (VDC) to measure the voltage between the power supply pin at the RF air spring solenoid harness connector and a known good chassis ground. Expect battery voltage (approximately 12V). If no voltage is present, trace the power supply circuit for an open, blown fuse, or ASCM output issue.
   • Ground Circuit Integrity Test (Ignition ON, solenoid disconnected): With the DMM, check for a good ground at the ground pin of the RF air spring solenoid harness connector by measuring voltage between it and the battery positive terminal. Expect approximately battery voltage. If significantly less, the ground circuit is compromised.
4. Wiggle Test: While performing continuity or voltage tests on the harness, gently wiggle the wiring harness and connectors along their length. Observe the DMM readings for any intermittent fluctuations, which would indicate a poor connection or intermittent open.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace the RF Air Spring Solenoid/Assembly: If the DMM resistance test across the solenoid itself indicates an open circuit, the solenoid is internally faulty. In many applications, the solenoid is an integral part of the air spring assembly and cannot be serviced separately, requiring replacement of the entire air spring unit. Use genuine OEM or high-quality aftermarket components for reliability.
• Repair or Replace Damaged Wiring Harness: If the visual inspection or continuity tests revealed a break, severe corrosion, or chafing in the wiring harness, the damaged section must be repaired. Use proper automotive wiring repair techniques, including soldering, heat-shrink tubing, and appropriate gauge wire. If damage is extensive, consider replacing the entire harness section.
• Clean and Secure Electrical Connectors: If corrosion or poor pin tension was identified, use a specialized electrical contact cleaner to meticulously clean all terminals. Carefully re-tension any spread pins using a suitable pin-tightening tool. Apply a small amount of dielectric grease to prevent future corrosion before reassembly. Replace the connector if pins are severely damaged or the plastic housing is cracked.
• Replace Blown Fuse: If a blown fuse related to the solenoid’s power supply was identified, replace it with a fuse of the correct amperage. However, investigate why the fuse blew, as it could indicate a downstream short circuit that might lead to another open if the fuse blows again.
• Replace the Air Suspension Control Module (ASCM): This is typically a last resort, pursued only after thoroughly ruling out the solenoid, wiring, and connectors. ASCM failure can be costly and often requires specialized programming or calibration after installation. Ensure all power and ground supplies to the ASCM are verified before condemning the module.
• Clear DTCs and Perform Functional Test: After completing any repairs, clear the C1874 code and any other related DTCs using a scan tool. Perform a functional test of the air suspension system, commanding ride height adjustments and verifying proper operation across all corners of the vehicle. Many air suspension systems require a calibration or initialization procedure after component replacement, particularly for the control module or height sensors; ensure this is performed according to manufacturer specifications.