What is XCMG XE750D Fault Code 33298 SPN91 FMI3?

Fault Code 33298 (SPN 91, FMI 3) indicates a voltage above normal or shorted high condition in the accelerator pedal position sensor circuit. This code is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the throttle position sensor, typically exceeding 4.5-5.0 volts on the sensor's output circuit.

On the XCMG XE750D excavator, this fault directly impacts engine speed control and responsiveness. The accelerator pedal position sensor (APPS) communicates operator input to the ECM, which then regulates fuel delivery and engine RPM. When SPN 91 FMI 3 activates, the system cannot accurately interpret throttle commands, potentially causing erratic engine behavior or triggering protective derate modes that limit machine performance to prevent damage.

Common Symptoms

• Check Engine Light or malfunction indicator lamp illuminated on the instrument cluster
• Engine may enter limp mode, restricting maximum RPM to 1200-1500 regardless of pedal input
• Unresponsive or erratic throttle response when operating hydraulic functions
• Engine may default to idle speed or fixed intermediate RPM
• Intermittent surging or hunting at operating speeds, especially under load

Potential Causes

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

• Damaged or corroded wiring harness between the accelerator pedal assembly and ECM, particularly at flex points near the cab mount or undercarriage
• Failed accelerator pedal position sensor, often due to moisture ingress or internal potentiometer wear after 5,000+ operating hours
• Shorted sensor signal wire making contact with the 5-volt reference supply or battery voltage
• Corroded or loose connector pins at the pedal assembly (common failure point on machines operating in wet/muddy conditions)
• ECM internal fault causing incorrect voltage supply to the sensor circuit (rare but possible on high-hour machines)

How to Troubleshoot and Fix Code 33298 SPN91 FMI3

Step 1: Visual Inspection Inspect the accelerator pedal wiring harness from the pedal assembly to the ECM connector. On used excavators, check for harness chafing against metal edges near the operator seat pivot and cab floor penetrations. Look for damaged insulation, exposed copper, or corroded connectors.

Step 2: Sensor Circuit Testing Using a digital multimeter, backprobe the accelerator pedal connector with the key ON, engine OFF. Measure voltage on the signal wire (typically pin 2)—normal reading should be 0.5-0.8 volts at idle pedal position. Check the 5-volt reference supply (pin 1) and ground circuit (pin 3). Resistance between signal and ground should exceed 10,000 ohms with the sensor disconnected.

Step 3: Component Testing Disconnect the pedal assembly and measure internal resistance across sensor terminals while slowly depressing the pedal. Resistance should change smoothly from approximately 1,000-4,000 ohms without spikes or dropouts. Replace the APPS assembly if readings are erratic or exceed specifications.

Step 4: Harness Continuity Check With both ends disconnected, test for continuity and shorts between all three sensor wires and chassis ground. Any reading below 10,000 ohms indicates a short circuit requiring harness repair or replacement.

For used excavators: Pay special attention to connector corrosion and previous repair attempts. Clean all pins with electrical contact cleaner and apply dielectric grease before reconnection.

Disclaimer: This guide provides general troubleshooting information. Always consult the XCMG service manual for your specific machine serial number and consider professional diagnostic assistance for complex electrical issues.