What is Sany Excavator Fault Code P2128?

Fault Code P2128 indicates "Accelerator Pedal Position Sensor E Circuit High Input" in Sany excavators. This diagnostic trouble code (DTC) is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the Accelerator Pedal Position (APP) Sensor circuit E, specifically the redundant sensor channel used for signal verification.

The APP sensor is a critical component in modern electronically-controlled diesel engines, converting the operator's pedal input into electrical signals that command fuel delivery and engine speed. Sany excavators utilize dual or triple redundant APP sensors for safety and accuracy. When the ECM detects a voltage reading above the manufacturer's specified threshold (typically above 4.5-4.8 volts) on sensor circuit E, it sets P2128 to prevent unintended acceleration or erratic engine behavior. This is particularly important in used excavators where sensor degradation can compromise operational safety.

Common Symptoms

• Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine derate mode activated, limiting maximum RPM to 1500-1800 RPM regardless of pedal input
• Erratic throttle response or engine surging, especially during initial pedal application
• Limp mode engagement where the machine operates at reduced power output to protect the drivetrain
• Intermittent loss of throttle control, requiring key cycle to temporarily restore function

Potential Causes

• Worn or damaged APP sensor internal potentiometer due to accumulated operating hours (common in machines exceeding 5,000 hours)
• Corroded or moisture-infiltrated connector pins at the pedal assembly or ECM harness connection points
• Wiring harness chafing or short to voltage along routing paths near the cab floor, pedal linkage, or through bulkhead grommets
• 5-volt reference voltage supply issue from the ECM affecting multiple sensor circuits simultaneously
• ECM internal fault in the sensor input processing circuitry (less common but possible in older machines)
• Aftermarket pedal installation or previous repair work with incorrect sensor specifications

How to Troubleshoot and Fix Code P2128

Step 1: Visual Inspection and Connector Examination Begin by disconnecting the battery negative terminal. Locate the APP sensor connector at the pedal assembly (typically under the operator's cab floor panel). Inspect for corrosion, bent pins, or moisture intrusion—critical checks for used excavators exposed to harsh environments. Examine the entire wiring harness from pedal to ECM for abrasion points, especially where harnesses pass through metal brackets or near moving components.

Step 2: Electrical Testing with Multimeter Using a digital multimeter (DMM), backprobe the APP sensor connector with the ignition ON but engine OFF. Measure the 5-volt reference voltage supply wire (consult Sany wiring diagrams for pin identification). Verify the sensor E circuit voltage at idle pedal position—should read 0.5-1.0 volts. Slowly depress the pedal while monitoring voltage; it should increase smoothly to 4.0-4.5 volts at full depression without spikes or dropouts. A reading consistently above 4.6 volts confirms the high input condition.

Step 3: Component Replacement and Calibration If voltage readings are abnormal, disconnect the sensor and test harness continuity to the ECM and check for short to battery voltage (should show infinite resistance). Replace the APP sensor assembly with OEM or equivalent quality parts—aftermarket sensors often cause repeat failures in used equipment. After installation, use Sany diagnostic software or compatible scan tool to perform pedal position sensor calibration/relearn procedure and clear codes. Test operation through full pedal range before returning to service.

For used excavators, always inspect harness routing for previous repair attempts or zip-tie modifications that create new wear points.

---

Disclaimer: This guide provides general troubleshooting information. Always consult the manufacturer's service manual specific to your Sany excavator model and serial number. If unfamiliar with electrical diagnostics or high-voltage systems, seek assistance from a certified heavy equipment technician.