Sany SY6HK1 Fault Code P2128(122): Complete Diagnostic Guide

What is Sany SY6HK1 Fault Code P2128(122)?

Fault Code P2128(122) indicates a Throttle/Pedal Position Sensor/Switch E Circuit High Input condition on the Sany SY6HK1 excavator. This code triggers when the Engine Control Module (ECM) detects an abnormally high voltage signal from the accelerator pedal position sensor (APPS), specifically the "E" circuit, which typically monitors redundant sensor circuitry for safety validation.

This fault directly affects the machine's throttle response system. The APPS sends critical voltage signals to the ECM to control engine speed and power output. When the ECM receives a voltage reading above the manufacturer's specified threshold (usually above 4.8-5.0 volts), it registers this fault to prevent unintended acceleration or engine runaway conditions. For the SY6HK1's Isuzu or Yanmar diesel engine, precise throttle control is essential for coordinating hydraulic pump demand with engine output.

Common Symptoms

Operators experiencing Code P2128(122) typically report:

• Engine derate mode or limited maximum RPM (often restricted to 1500-1800 RPM regardless of pedal input)
• Check Engine Light (CEL) or malfunction indicator lamp illuminated on the instrument cluster
• Erratic throttle response where engine speed doesn't correlate with pedal position, or sudden surging
• Hydraulic system underperformance due to insufficient engine speed affecting pump flow
• Intermittent loss of throttle control, particularly when operating on rough terrain (indicating possible wiring issues)

Potential Causes

The most common technical failures triggering P2128(122) on used SY6HK1 excavators include:

• Accelerator pedal position sensor internal failure (worn potentiometer tracks causing voltage spikes)
• Wiring harness damage at known rub points: beneath the operator cab mounting bolts, along the right-side chassis rail, or where harnesses pass through the rotating house junction
• Corroded or moisture-contaminated connectors on the APPS multi-pin connector (typically a 6-pin Deutsch or AMP-style connector)
• Short to power (12V/24V) in the sensor signal wire due to insulation breakdown from heat or abrasion
• ECM internal fault (less common) where the analog-to-digital converter circuit fails
• Aftermarket pedal assembly installation with incompatible voltage output ranges

How to Troubleshoot and Fix Code P2128(122)

Step 1: Initial Inspection and Code Verification

Connect a diagnostic scanner compatible with Sany equipment (SY-Scanner or equivalent OBD-II tool). Record all active and pending codes. Clear the fault and attempt to replicate the issue. If the code returns immediately without pedal input, suspect wiring or ECM issues rather than sensor failure.

Step 2: Accelerator Pedal Position Sensor Testing

Locate the APPS (mounted on the pedal assembly beneath the operator station). Disconnect the sensor connector and inspect for:

• Corrosion, moisture, or bent pins (common in used machines exposed to cab leaks)
• Oil contamination from hydraulic system leaks

Using a digital multimeter, backprobe the sensor connector with the key ON, engine OFF:

• Measure supply voltage (should be 5.0V ±0.25V on the reference wire)
• Check ground continuity (less than 0.5 ohms to chassis ground)
• Slowly depress the pedal while monitoring sensor output voltage on circuit E (should sweep smoothly from approximately 0.5V at idle to 4.5V at full throttle)

A reading consistently above 4.8V or erratic jumps indicate sensor replacement is necessary. OEM Sany part number or quality aftermarket equivalents (TPS/APPS rated for heavy-duty diesel applications) should be used.

Step 3: Wiring Harness Inspection

For used excavators, physical harness inspection is critical. Trace the APPS wiring from the pedal to the ECM (located in the right-side electrical cabinet):

• Inspect harness routing near the cab pivot points and hydraulic tank
• Check for wear marks where harnesses contact metal edges (use electrical tape or split loom as temporary fixes)
• Perform a resistance test on each wire (should be less than 2 ohms end-to-end)
• Test for short to power: disconnect both sensor and ECM connectors, measure resistance between signal wire E and battery positive (should be infinite/OL)

Replace damaged sections with OEM-spec 20-22 AWG shielded cable, ensuring proper grounding of shield drain wires.

Step 4: ECM Evaluation

If sensor and wiring test normal, the ECM may have a failed input channel. This requires dealer-level diagnostics with Sany's proprietary software to monitor live sensor data streams. ECM replacement or repair should only be attempted after confirming correct sensor supply voltage output from the module itself (test at ECM connector pin-out).

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Disclaimer: This guide provides general troubleshooting information for Code P2128(122). Always consult the official Sany service manual for your specific serial number and model year. For used excavators with unknown service history, professional diagnosis by a certified Sany technician or qualified diesel mechanic is recommended before replacing major components like the ECM.