What is Volvo Excavator Fault Code 128 PID 174 FMI 2?

Fault Code 128 PID 174 FMI 2 indicates that the Engine Control Module (ECM) has detected an intermittent or erratic signal from the Fuel Temperature Sensor. PID 174 specifically references fuel temperature, while FMI 2 denotes data that is erratic, intermittent, or incorrect. This fault affects the ECM's ability to accurately calculate fuel density and optimize injection timing, which is critical for Volvo excavators' fuel efficiency and emissions control.

The fuel temperature sensor provides real-time data that allows the ECM to compensate for fuel density changes caused by temperature variations. When this sensor sends unreliable signals, the engine may run in a protective derate mode to prevent damage. In used Volvo excavators, this code often appears due to sensor degradation, corroded connections, or damaged wiring harnesses exposed to years of vibration and environmental conditions.

Common Symptoms

• Check Engine Light or Warning Lamp illuminated on the operator display
• Power derate or reduced engine performance, particularly under heavy load conditions
• Rough idle or inconsistent engine RPM fluctuations
• Increased fuel consumption due to improper fuel density compensation
• Intermittent fault that may disappear and reappear during operation, especially during temperature changes

Potential Causes

• Corroded or loose electrical connectors at the fuel temperature sensor (common in high-hour used machines)
• Damaged wiring harness caused by rubbing against engine components or frame rails
• Failed fuel temperature sensor due to internal resistance drift or element degradation
• Poor ground connections in the engine harness affecting sensor signal integrity
• ECM software issues or calibration problems (less common but possible in older units)
• Fuel contamination or water intrusion affecting sensor operation
• Connector pin corrosion from moisture infiltration in the engine bay

How to Troubleshoot and Fix Code 128 PID 174 FMI 2

Step 1: Visual Inspection Begin by locating the fuel temperature sensor on the fuel rail or fuel filter housing. Inspect the sensor connector for corrosion, bent pins, moisture, or oil contamination. On used excavators, carefully trace the wiring harness from the sensor to the ECM, looking for chafing points, worn insulation, or areas where the harness contacts moving components.

Step 2: Electrical Testing Using a digital multimeter, check the sensor's resistance values. Disconnect the sensor and measure resistance across the sensor terminals—typical values range from 2,000-3,000 ohms at room temperature, but consult Volvo specifications for your specific model. Test the supply voltage at the connector (typically 5 volts) and verify the ground circuit has less than 0.1 ohms resistance.

Step 3: Signal Testing With Volvo VCADS (Volvo Computer Aided Diagnostic System) or compatible diagnostic software, monitor the fuel temperature reading in real-time while the engine warms up. The reading should increase smoothly without sudden jumps or dropouts. Erratic values confirm sensor or wiring issues.

Step 4: Connector and Harness Repair For used machines, thoroughly clean all connector pins with electrical contact cleaner and apply dielectric grease to prevent future corrosion. Repair any damaged harness sections with proper gauge wire and heat-shrink connectors. Replace the entire harness section if multiple wear points exist.

Step 5: Component Replacement If testing confirms sensor failure, replace with a genuine Volvo or OEM-equivalent fuel temperature sensor. After replacement, clear the fault code and perform a test cycle to verify proper operation.

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Disclaimer: This guide provides general diagnostic information. Always consult Volvo service manuals and qualified diesel technicians for your specific excavator model. Improper repairs may void warranties or cause equipment damage.