What is Sany Excavator Fault Code P981?

Fault Code P981 indicates a malfunction in the Engine Control Module (ECM) communication circuit or a critical internal ECM error within Sany excavators. This code typically signals that the ECM has detected an abnormal voltage level, corrupted data transmission, or a complete loss of communication between the engine controller and other machine systems. In Sany equipment, this fault directly impacts the CAN bus network, which coordinates communication between the engine, hydraulic system, and display panel.

This code is critical because the ECM serves as the machine's central processor, controlling fuel injection timing, emissions systems, and power output. When communication fails, the excavator may enter a protective derate mode or experience complete shutdown to prevent catastrophic engine damage. For used excavators, this fault often relates to aging wiring harnesses or corroded connection points rather than actual ECM failure.

Common Symptoms

• Engine warning light illuminated on the instrument cluster with possible "Check Engine" message
• Sudden engine power loss or automatic derate to limited RPM (often 1200-1500 RPM maximum)
• Intermittent starting issues or complete failure to crank when ECM communication is lost
• Hydraulic system sluggishness due to reduced engine performance and electronic control interference
• Display panel errors showing multiple fault codes simultaneously or blank screens during operation

Potential Causes

The most common technical reasons for Code P981 in used Sany excavators include:

• Corroded or loose ECM connector pins, particularly at the 48-pin main harness connection exposed to moisture intrusion
• Damaged CAN bus wiring at known rub points near the engine mount brackets and along the boom base where harnesses flex repeatedly
• Failed ECM internal components due to voltage spikes from alternator irregularities or jump-start procedures on older machines
• Poor ground connections at the engine block or chassis ground straps that have oxidized over time
• Water ingress into the ECM housing, common in machines operating in wet environments without proper sealing maintenance

How to Troubleshoot and Fix Code P981

Step 1: Visual Inspection Begin by thoroughly inspecting the ECM and all associated wiring harnesses. Check the main ECM connector for bent pins, corrosion (green/white deposits), or moisture inside the connector boot. On used excavators, pay special attention to harness routing where cables contact metal edges or moving components.

Step 2: Electrical Testing Using a digital multimeter, verify battery voltage (should read 12.0-14.5V) at the ECM power supply pins with the key on. Check ground circuit resistance between the ECM ground pin and battery negative—readings above 0.5 ohms indicate poor grounding. Test CAN bus communication lines (typically CAN-High and CAN-Low) for proper voltage levels: CAN-High should read approximately 3.5V and CAN-Low around 1.5V during normal operation.

Step 3: Advanced Diagnostics Connect Sany-specific diagnostic software (PC-E software or compatible tool) to read live ECM data streams. Monitor for communication dropouts or error frames on the CAN network. If communication is stable but the code persists, perform an ECM voltage supply test under load conditions. For used machines, consider replacing the ECM relay and inspecting the alternator output for voltage spikes exceeding 15V, which can damage sensitive electronics.

Step 4: Component Replacement If diagnostics confirm ECM failure, ensure the replacement unit matches the machine's software version and hardware specifications. Before installing a new or remanufactured ECM, clean all connector contacts with electrical contact cleaner and apply dielectric grease to prevent future corrosion.

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Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual for your specific model and consider professional diagnostic services for complex electrical issues, especially when dealing with critical engine control systems.