What is Caterpillar Fault Code 113?

Caterpillar Fault Code 113 indicates an Intake Manifold Air Temperature (IMAT) sensor circuit voltage is above normal or shorted high. This diagnostic trouble code (DTC) is triggered when the Electronic Control Module (ECM) detects an abnormally high voltage signal from the intake air temperature sensor, typically above 4.5 volts when normal operating range is 0.5-4.5 volts.

The IMAT sensor plays a critical role in engine performance by measuring the temperature of air entering the combustion chamber. The ECM uses this data to calculate proper fuel injection timing and quantity, optimize air-fuel ratios, and control emissions systems. When this sensor reports incorrect data due to circuit faults, the engine management system cannot accurately adjust for varying operating conditions, potentially leading to reduced power output, increased fuel consumption, and elevated emissions levels.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the dashboard
• Reduced engine power or noticeable performance derate, especially during cold starts or temperature extremes
• Hard starting conditions or extended cranking time before engine fires
• Black smoke from exhaust due to improper fuel-to-air mixture calculations
• Poor fuel economy as the ECM defaults to preset values instead of real-time temperature compensation

Potential Causes

The most common technical causes for Code 113 in used Caterpillar excavators include:

• Damaged or corroded wiring harness at the sensor connector, especially where harnesses run near hot exhaust components or rub against frame members
• Failed IMAT sensor with internal short circuit or degraded thermistor element (common in machines with 5,000+ operating hours)
• Chafed wiring along the intake manifold where vibration causes insulation wear over time
• Moisture intrusion into the sensor connector causing short circuits to voltage supply wire
• ECM internal fault (rare, but possible in older machines with environmental exposure)
• Aftermarket wiring repairs done incorrectly on used equipment, creating voltage supply issues

How to Troubleshoot and Fix Code 113

Step 1: Visual Inspection Begin with a thorough inspection of the IMAT sensor and its wiring harness. The sensor is typically located on the intake manifold near the air inlet. Check for physical damage, oil contamination, corroded pins, or loose connections. On used excavators, pay special attention to harness routing where cables contact hot surfaces or metal edges—these are common failure points.

Step 2: Electrical Testing Disconnect the IMAT sensor connector and use a digital multimeter to check resistance across the sensor terminals. At 68°F (20°C), resistance should typically read 2,000-3,000 ohms (consult your specific service manual for exact specifications). If the reading shows infinite resistance or zero ohms, the sensor has failed internally and requires replacement.

Step 3: Circuit Voltage Check With the sensor disconnected and ignition on (engine off), measure voltage at the harness connector (machine side). You should see approximately 5 volts on the signal wire. If voltage reads near battery voltage (12-24V), there's a short to power somewhere in the harness between the sensor and ECM.

Step 4: Harness Continuity Test Check for shorts to ground or shorts to voltage along the entire sensor circuit. Inspect wire insulation carefully where the harness passes through grommets or secures to brackets. On used machines, corrosion inside connectors can create intermittent high-resistance connections that appear as voltage spikes to the ECM.

Step 5: Repair or Replace Replace the IMAT sensor if testing confirms sensor failure (most common solution). If wiring damage is found, repair using proper gauge wire with heat-shrink connections and secure routing away from heat sources. Clear codes using Caterpillar Electronic Technician (Cat ET) software and verify repair with a test run under load.

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Disclaimer: This guide provides general troubleshooting information for Caterpillar Fault Code 113. Always consult your machine's specific service manual and consider professional diagnostic services for complex electrical issues. Improper repairs may cause additional damage or safety hazards.