What is Caterpillar Fault Code EID671?

Caterpillar fault code EID671 indicates an Engine Inlet Air Temperature Sensor Circuit Malfunction, signaling that the Engine Control Module (ECM) has detected an abnormal voltage reading from the intake air temperature sensor circuit. This diagnostic trouble code specifically points to electrical issues within the sensor circuit rather than actual temperature anomalies, affecting the ECM's ability to properly calculate air density for optimal fuel injection timing and quantity.

This code is critical for Caterpillar excavators because the ECM relies on accurate inlet air temperature data to adjust the air-fuel ratio and maintain proper combustion efficiency. When EID671 triggers, the ECM switches to default values, which can result in reduced engine performance, increased fuel consumption, and potential long-term damage to engine components due to improper combustion temperatures.

Common Symptoms

When fault code EID671 is active on your Caterpillar excavator, operators typically experience:

• Check Engine Warning Light illuminated on the instrument cluster with possible derate notification
• Reduced engine power output, particularly noticeable during heavy digging or lifting operations
• Rough idle or inconsistent engine RPM fluctuations, especially during cold starts
• Increased black smoke from the exhaust due to rich fuel mixture compensation
• Poor fuel economy as the ECM operates on conservative default air temperature values

Potential Causes

The most common technical reasons for EID671 appearing on used Caterpillar excavators include:

• Intake Air Temperature (IAT) Sensor failure due to carbon buildup, internal element degradation, or moisture intrusion
• Damaged or corroded wiring harness connections at the sensor plug or ECM terminals
• Chafed or pinched sensor wiring, particularly at known rub points near the air intake manifold mounting brackets
• Poor ground connection affecting the sensor's reference voltage circuit
• Corrosion on connector pins caused by water infiltration through damaged seals (common in used machines operating in wet conditions)
• ECM internal circuit failure (rare, but possible in high-hour machines)

How to Troubleshoot and Fix Code EID671

Step 1: Visual Inspection Begin by locating the intake air temperature sensor on the air inlet manifold. Inspect the sensor body for physical damage, cracks, or carbon deposits. Examine the entire wiring harness from sensor to ECM for obvious abrasion, cuts, or burn marks at known friction points where the harness contacts frame members.

Step 2: Electrical Testing Disconnect the sensor connector and use a digital multimeter to measure sensor resistance. At 68°F (20°C), resistance should typically read between 2,000-3,000 ohms (consult your specific service manual for exact specifications). Check for proper reference voltage (usually 5 volts) at the harness connector with ignition on, engine off.

Step 3: Circuit Continuity and Ground Testing Test continuity between the sensor connector and ECM pins using wiring diagrams from Caterpillar Electronic Technician (ET) software. Measure resistance to ground on both signal and reference circuits—readings below 10,000 ohms indicate a short to ground. For used excavators, pay special attention to connector corrosion; clean terminals with electrical contact cleaner and apply dielectric grease.

Step 4: Component Replacement If sensor resistance is out of specification or circuit testing reveals wiring faults, replace the defective component. When installing a new IAT sensor on used equipment, always replace the connector pigtail if corrosion or heat damage is evident, as this prevents recurring codes.

---

Disclaimer: This guide provides general troubleshooting information. Always consult your Caterpillar service manual and consider professional diagnostic assistance for complex electrical issues or if you lack proper diagnostic tools.