C1870

What Does Code C1870 Mean?

DTC C1870 signifies an “Air Suspension Gate Solenoid Output Circuit Open” fault detected by the vehicle’s Suspension Control Module (SCM) or Powertrain Control Module (PCM), depending on the vehicle architecture. This code indicates that the control module monitoring the air suspension system has identified an open circuit condition in the electrical pathway leading to or within a specific “gate solenoid.” The gate solenoid is a crucial component, typically a normally closed or normally open valve within the air suspension’s distribution block or integrated into the compressor assembly, responsible for regulating the flow of compressed air. It may control air passage to individual air springs, to a reservoir, or act as a system isolation valve. When an open circuit is detected, it means the control module is unable to establish proper electrical continuity to operate the solenoid, preventing it from activating as commanded. This usually manifests as an abnormally high resistance or infinite resistance reading on the solenoid’s circuit, indicating a break in the wiring, a poor connection, or an internal failure of the solenoid’s coil itself. Consequently, the air suspension system loses precise control over air routing and pressure management through this specific gate, impacting ride height, vehicle leveling, and overall suspension performance.

Common Symptoms

• Illuminated air suspension warning light on the instrument cluster.
• Vehicle exhibiting uneven ride height, sagging on one or more corners, or consistently riding too low or too high.
• Air compressor running excessively or cycling more frequently than normal, attempting to compensate for uncontrolled air flow.
• Noticeably harsher or less comfortable ride quality due to improper air spring pressure.
• Delayed or failed ride height adjustments when driving or after vehicle start-up.
• Audible hissing sounds indicating an air leak, potentially from the gate solenoid itself if it fails in an open position or due to associated component stress.

What Causes the Code C1870?

• Faulty Air Suspension Gate Solenoid: The most common cause is an internal open circuit within the solenoid coil itself, preventing current flow and activation.
• Wiring Harness Damage: An open circuit in the wiring harness connecting the SCM/PCM to the gate solenoid. This can result from chafing, cuts, corrosion, or physical damage to the conductors.
• Poor Electrical Connections: Loose, corroded, or damaged terminal pins at either the solenoid connector or the SCM/PCM connector, leading to intermittent or complete loss of electrical continuity.
• Faulty Suspension Control Module (SCM) / Powertrain Control Module (PCM): Less common, but an internal failure of the output driver circuit within the control module responsible for operating the gate solenoid can cause it to falsely detect an open circuit or fail to supply the necessary power/ground.

How to Diagnose and Troubleshoot

Diagnosis of C1870 requires a systematic approach, often involving a diagnostic scanner and a digital multimeter (DMM).

1. Retrieve and Document DTCs: Use an advanced OBD-II scanner to confirm C1870 and check for any related or accompanying air suspension codes. Record freeze frame data, as it can provide critical information about vehicle conditions when the fault occurred.
2. Visual Inspection:
   • Locate the air suspension gate solenoid (often part of an air distribution block or valve block).
   • Inspect the wiring harness leading to the solenoid for any visible signs of damage, chafing against sharp edges, melted insulation, or corrosion, especially where it passes through bulkheads or near wheel wells.
   • Examine the electrical connector at the solenoid and the relevant connector at the SCM/PCM for bent pins, corrosion, or looseness.
3. Perform Solenoid Resistance Test:
   • With the ignition OFF, disconnect the electrical connector from the air suspension gate solenoid.
   • Using a DMM set to ohms, measure the resistance across the two terminals of the solenoid itself.
   • Compare this reading to the manufacturer’s specifications (typically a few ohms to several tens of ohms). An infinite resistance reading (open circuit) confirms an internal fault within the solenoid. If the reading is within specification, the solenoid itself is likely not the cause of the open circuit.
4. Wiring Harness Continuity Test:
   • With the solenoid connector disconnected and the corresponding SCM/PCM connector disconnected, identify the specific wires for the gate solenoid circuit. Consult the vehicle’s wiring diagrams.
   • Using the DMM set to ohms, check for continuity between the SCM/PCM connector pin and the solenoid connector pin for both the power/control wire and the ground wire. You should read very low resistance (typically less than 0.5 ohms).
   • An infinite reading on either wire indicates an open circuit within the wiring harness.
   • Additionally, check both wires for shorts to ground and shorts to power. You should have infinite resistance when testing against vehicle ground and against a known B+ source.
5. Power and Ground Supply Check (at Solenoid Connector):
   • Reconnect the SCM/PCM connector. With the ignition ON, and potentially with the engine running or the suspension system active, check for the proper power supply voltage (usually battery voltage or a specific control voltage) at the solenoid connector using the DMM or a test light.
   • Verify a good ground connection at the solenoid connector by testing continuity to a known good chassis ground or by checking for voltage drop across the ground wire.
   • Note: Some solenoids are ground-side switched by the control module, meaning power is constant and the module provides the ground to activate. Consult wiring diagrams.
6. Bi-Directional Control Test (if scanner equipped): If your diagnostic scanner has bi-directional control capabilities, attempt to command the air suspension gate solenoid ON and OFF. While commanding, listen closely for an audible click from the solenoid. If no click is heard, and the wiring and power/ground tests pass, it further points to an internal solenoid failure.

Recommended Repairs and Solutions

Once the root cause of the C1870 code has been accurately identified through thorough diagnostics, the following repairs and solutions are typically recommended:

• Repair or Replace Wiring Harness: If an open circuit is located within the wiring harness, the damaged section should be professionally repaired. This involves splicing in a new section of wire using appropriate gauge wire, heat-shrink butt connectors, and ensuring all repairs are sealed against moisture and vibration. In cases of extensive damage, replacement of the entire harness segment may be necessary.
• Clean or Repair Electrical Connections: Address any corroded or loose terminals at either end of the circuit. Clean connector pins with electrical contact cleaner, use a terminal pick to gently reshape any bent pins, and apply dielectric grease to protect against future corrosion before reassembly. Ensure connectors click securely into place.
• Replace Air Suspension Gate Solenoid: If the solenoid itself tests as an open circuit internally or fails to activate during bi-directional tests despite proper power and ground supply, it must be replaced. These solenoids are often integral components of an air distribution block or valve block, and in many cases, the entire block may need to be replaced rather than just the individual solenoid. Always use OEM-quality replacement parts for critical air suspension components.
• Replace Suspension Control Module (SCM) / Powertrain Control Module (PCM): This should be considered a last resort, only after all other components, wiring, and connections have been thoroughly tested and verified to be in perfect working order. A faulty SCM/PCM output driver can mimic an open circuit condition. If the module is replaced, it will almost certainly require programming and/or calibration to the vehicle’s specifications using specialized diagnostic equipment.
• Post-Repair Procedures: After any repair, clear the DTCs, perform any manufacturer-specified air suspension system calibration or learn procedures, and then conduct a thorough road test to ensure proper functionality and that the C1870 code does not return. Additionally, check for any air leaks in the system, especially if components like valve blocks were removed or disturbed.