What is Case Excavator Fault Code 107?

Fault Code 107 on Case excavators indicates an Air Inlet Heater (AIH) Circuit Low Voltage condition, meaning the Engine Control Module (ECM) has detected abnormally low voltage in the air inlet heater circuit, typically below the manufacturer's specified threshold of approximately 10 volts during heater activation.

This diagnostic trouble code specifically monitors the air intake heating system, which is critical for cold-start performance in diesel engines. The air inlet heater preheats incoming air to improve combustion efficiency during startup, especially in temperatures below 40°F (5°C). When the ECM detects insufficient voltage reaching the heater element or its control circuit, it triggers Code 107 to prevent potential starting issues and protect the electrical system from short circuits or component damage. For used Case excavators, this code often surfaces due to age-related electrical degradation rather than component failure.

Common Symptoms

• Extended cranking time during cold starts or failure to start in cold weather conditions
• Illuminated malfunction indicator lamp (MIL) or check engine light on the instrument cluster
• Stored fault code in ECM memory without immediate performance loss once engine reaches operating temperature
• Intermittent starting difficulties that worsen as ambient temperatures drop
• White or gray exhaust smoke during initial startup due to incomplete combustion

Potential Causes

The most common technical causes for Code 107 in used Case excavators include:

• Damaged or corroded wiring harness between the ECM and air inlet heater relay, particularly at connection points near the engine block where vibration and heat cycles cause insulation breakdown
• Failed air inlet heater element with internal open circuit or reduced resistance
• Faulty air inlet heater relay with worn contacts or coil failure preventing proper voltage delivery
• Corroded or loose connector pins at the heater assembly or relay socket—extremely common in machines with 3,000+ operating hours
• Degraded ground connection at the heater mounting point due to rust or paint buildup
• ECM internal fault in the heater control circuit driver (rare but possible in high-hour machines)

How to Troubleshoot and Fix Code 107

Step 1: Visual Inspection and Connector Assessment Begin by inspecting the air inlet heater wiring harness from the ECM to the heater assembly. Check for abraded insulation, especially where the harness contacts the engine block or frame rails. Disconnect the heater connector and inspect pins for green corrosion, bent contacts, or moisture intrusion. Clean contacts with electrical contact cleaner and dielectric grease.

Step 2: Electrical Testing with Multimeter Using a digital multimeter, measure resistance across the air inlet heater element terminals (disconnected). Typical resistance should range between 0.5-2.0 ohms depending on heater specification. An open circuit (infinite resistance) indicates element failure. Next, check for supply voltage at the heater connector with ignition on—you should see battery voltage (12-14V) when the system activates.

Step 3: Relay and Circuit Verification Locate the air inlet heater relay in the machine's relay panel. Swap it with an identical relay to rule out relay failure. If symptoms persist, use your multimeter to backprobe the ECM connector (without disconnecting) and verify the control signal wire shows appropriate voltage when commanded. For used excavators, pay special attention to harness routing near exhaust components where heat damage commonly occurs, and inspect all ground points for tight, corrosion-free connections.

Step 4: Component Replacement and System Reset Replace confirmed failed components—heater element, relay, or damaged harness sections. After repairs, clear fault codes using Case diagnostic software (ServiceMaster or compatible scan tool) and perform a cold-start test cycle to verify proper operation.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Case service manual for your specific model and serial number. If you're uncomfortable performing electrical diagnostics, consult a certified heavy equipment technician to prevent further damage or safety hazards.