What is Case Excavator Fault Code 1173?

Fault Code 1173 indicates an Injector Cylinder #5 Circuit High Voltage condition. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormally high voltage reading in the electrical circuit controlling the fuel injector for cylinder number five, exceeding the manufacturer's specified threshold (typically above 120 volts during operation).

This code specifically monitors the injector driver circuit within the ECM and the wiring harness connecting to injector #5. For Case excavators, this fault compromises fuel delivery precision to one cylinder, directly impacting engine performance, fuel efficiency, and emissions compliance. Left unaddressed, this condition can cause cylinder misfires, increased exhaust temperatures, and potential damage to the catalytic converter or diesel particulate filter (DPF).

Common Symptoms

• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument cluster
• Rough engine idle or noticeable vibration, especially when operating under light loads
• Loss of power (derate mode) with the engine limiting RPM to 1800 or lower to prevent damage
• Increased fuel consumption as the ECM compensates for the misfiring cylinder
• White or gray exhaust smoke during startup or acceleration, indicating incomplete combustion in cylinder #5

Potential Causes

The most common technical causes for Code 1173 on used Case excavators include:

• Open circuit or damaged wiring in the injector #5 harness, particularly at flex points near the valve cover where cables experience repeated bending
• Corroded or loose electrical connectors at the injector or ECM connection points—common in machines exposed to moisture or harsh environments
• Failed fuel injector solenoid with internal short circuits causing resistance irregularities
• ECM internal driver circuit failure for cylinder #5 (less common but possible in high-hour machines)
• Chafed wiring harness rubbing against engine components, valve covers, or brackets—a known issue on older Case models with brittle insulation

How to Troubleshoot and Fix Code 1173

Step 1: Visual Inspection Begin by inspecting the injector #5 wiring harness from the ECM to the injector. Look for visible damage, melted insulation, or wear points where the harness contacts metal surfaces. On used excavators, check for corrosion on connector pins and ensure all connections are firmly seated with intact locking tabs.

Step 2: Electrical Testing Using a digital multimeter (DMM), disconnect the injector #5 connector and measure resistance across the injector solenoid terminals (typical specification: 0.3-0.8 ohms). Next, check for short-to-voltage by measuring between each injector wire and battery positive with the ignition off—any reading indicates harness damage. Inspect connector terminals for bent pins or moisture intrusion.

Step 3: ECM and Harness Verification If injector resistance is within specification, test the ECM driver circuit by back-probing the injector connector while cranking the engine. You should see pulsing voltage (typically 90-110V peak). Absence of signal indicates potential ECM failure. For used machines, consider swapping the #5 injector with another cylinder to determine if the fault follows the component or remains with the circuit.

Step 4: Component Replacement Replace damaged harness sections using OEM-spec wiring with proper heat-shrink connections. If the injector tests faulty, install a genuine or quality remanufactured replacement. Always apply dielectric grease to connectors on reassembly to prevent future corrosion.

Disclaimer: This guide provides general troubleshooting information. Always consult your Case service manual for model-specific procedures and torque specifications. For complex electrical diagnostics or ECM programming, professional service with Case diagnostic software (ServiceMaster or equivalent) is recommended.