What is Caterpillar Fault Code SPN1073?

SPN 1073 indicates an Exhaust Gas Temperature (EGT) Sensor Circuit High Voltage condition in Caterpillar diesel engines. This diagnostic trouble code triggers when the Engine Control Module (ECM) detects an abnormally high voltage signal from the exhaust gas temperature sensor, typically reading above 4.5 volts when normal operating range is 0.5-4.5 volts.

The EGT sensor monitors exhaust temperatures to protect critical aftertreatment components like the Diesel Particulate Filter (DPF) and Diesel Oxidation Catalyst (DOC). This sensor is essential for the ECM to properly manage regeneration cycles and prevent catastrophic thermal damage to emissions equipment. When SPN1073 appears, the ECM cannot accurately monitor exhaust temperatures, potentially leading to incomplete regenerations, reduced engine performance, and possible damage to expensive aftertreatment systems.

Common Symptoms

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine derate or power reduction mode, limiting machine to 75% power or lower
• Failed or incomplete DPF regeneration cycles, causing excessive soot accumulation
• High exhaust temperature warnings appearing intermittently or continuously
• Diagnostic system displaying active fault code during Electronic Technician (ET) software scan

Potential Causes

The most frequent causes of SPN1073 in used Caterpillar excavators include:

• Open circuit in the EGT sensor wiring harness due to wire breakage or connector damage
• Corroded or loose connectors at the sensor or ECM connection points (extremely common in high-hour machines)
• Failed EGT sensor with internal circuit failure causing constant high voltage output
• Chafed or rubbed wiring along the exhaust system where harnesses contact hot surfaces or frame components
• Moisture intrusion into sensor connectors causing short circuits or resistance changes
• ECM internal fault (rare, but possible in machines with electrical system damage history)

How to Troubleshoot and Fix Code SPN1073

Step 1: Visual Inspection Begin with a thorough inspection of the EGT sensor location (typically mounted in the exhaust manifold or downpipe). Check for physical damage, melted connectors, or obvious wire damage. On used excavators, carefully inspect harness routing for evidence of rubbing against the exhaust system or frame—a notorious wear point on older machines.

Step 2: Connector and Wiring Check Disconnect the EGT sensor connector and inspect pins for corrosion, bent terminals, or moisture. Clean contacts with electrical contact cleaner and apply dielectric grease. Using a digital multimeter (DMM), check for continuity between the sensor connector and the ECM pins according to your machine's wiring diagram.

Step 3: Sensor Resistance Testing Measure the EGT sensor resistance at the sensor connector with the harness disconnected. Typical resistance values range from 100-500 ohms at room temperature (consult your specific service manual). An open circuit (infinite resistance) confirms sensor failure.

Step 4: Voltage Signal Testing With the key on and engine off, backprobe the sensor signal wire at the ECM connector. You should read approximately 5 volts reference voltage. If voltage reads near battery voltage (12V+), suspect a short to power in the harness.

Step 5: Component Replacement If testing confirms sensor failure, replace the EGT sensor with a genuine Caterpillar or quality aftermarket part. For used machines, always replace the sensor pigtail connector simultaneously to prevent recurring issues from corroded terminals. Clear codes using Cat ET software and perform a regeneration test cycle.

Critical for Used Equipment: Before replacing expensive components, thoroughly inspect all harness protection and heat shielding. Many SPN1073 codes on high-hour excavators result from wiring deterioration rather than actual sensor failure.

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Disclaimer: This guide provides general troubleshooting information. Always consult your machine's specific service manual and consider professional diagnostic assistance for complex electrical issues. Improper repairs may cause additional damage or safety hazards.