What is XCMG XE750D Fault Code 33270 SPN91 FMI2?

Fault Code 33270 (SPN 91 FMI 2) indicates an erratic or intermittent signal from the Accelerator Pedal Position Sensor (APPS). This diagnostic trouble code (DTC) means the Engine Control Module (ECM) is receiving irregular data from the throttle position circuit, specifically showing values that fluctuate outside normal operating parameters.

SPN 91 refers to the Accelerator Pedal Position, while FMI 2 designates data erratic, intermittent, or incorrect. On the XCMG XE750D excavator, this sensor is critical for proper engine response and fuel delivery. The ECM relies on consistent voltage signals from the APPS to regulate engine speed and power output. When this communication breaks down, the machine's performance and safety systems are compromised, potentially triggering engine derating or limp mode to protect the powertrain.

Common Symptoms

• Engine hesitation or surging during operation, with inconsistent response to throttle input
• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the dashboard
• Engine derate mode activated, limiting maximum RPM to 1200-1500 range
• Erratic idle speed that fluctuates between high and low without pedal input
• Loss of power during digging or lifting operations, particularly under load

Potential Causes

The most common technical causes for this fault on used XCMG XE750D excavators include:

• Worn or damaged accelerator pedal position sensor with internal potentiometer degradation
• Corroded or loose wiring connections at the pedal sensor connector or ECM harness plugs
• Chafed or pinched wiring along the harness routing points, especially near the cab floor or pedal mounting bracket
• Contaminated sensor contacts from dirt, moisture, or hydraulic fluid intrusion in the cab
• Failing ECM with internal circuit board issues (less common but possible on high-hour machines)
• Poor ground connections at chassis grounding points causing voltage fluctuations

How to Troubleshoot and Fix Code 33270 SPN91 FMI2

Step 1: Visual Inspection Begin by examining the accelerator pedal assembly and its wiring harness. On used excavators, check for physical damage, worn insulation, or evidence of rubbing against metal surfaces. Inspect the connector pins for corrosion, bent terminals, or moisture intrusion—common issues in XCMG machines operating in harsh environments.

Step 2: Electrical Testing Using a digital multimeter, measure the voltage output from the APPS with the key in the ON position. The sensor typically has two circuits providing 0.5-4.5V DC signals. Check that voltage increases smoothly as you depress the pedal—any jumps, drops, or flat spots indicate sensor failure. Verify supply voltage (typically 5V reference) from the ECM and check ground continuity (should read less than 0.5 ohms resistance).

Step 3: Connector and Harness Repair Clean all connector terminals with electrical contact cleaner and apply dielectric grease. For used machines, pay special attention to harness routing—secure any loose wiring that may flex during operation. Check the harness grommet where wires pass through the cab floor for chafing damage.

Step 4: Component Replacement If testing confirms sensor failure, replace the complete accelerator pedal assembly with a genuine XCMG or quality aftermarket part. After installation, clear codes using diagnostic software (XCMG Excavator Diagnostic Tool or compatible J1939 scanner) and perform a calibration procedure per manufacturer specifications.

Disclaimer: This guide provides general troubleshooting information. For complex electrical diagnostics or component replacement on heavy equipment, consult a certified XCMG technician or qualified diesel mechanic with appropriate diagnostic tools and service manuals.