What is Sany Excavator Fault Code P820?

Fault Code P820 indicates a communication error or malfunction within the engine control module (ECM) network, specifically related to CAN bus communication failure or ECM internal processing issues. This diagnostic trouble code (DTC) signals that the engine control module is unable to properly communicate with other critical control systems on the Sany excavator, or the ECM itself has detected an internal fault that prevents normal operation.

This code is critical because the CAN (Controller Area Network) bus serves as the central nervous system for modern excavators, allowing the engine ECM, hydraulic controller, display panel, and other electronic modules to exchange real-time data. When P820 triggers, the excavator's integrated systems cannot coordinate properly, leading to reduced performance, safety system failures, or complete operational shutdown. For used Sany excavators, this fault often stems from age-related electrical deterioration rather than component design flaws.

Common Symptoms

• Warning lights illuminated on the instrument cluster, particularly the engine malfunction indicator and system error lights
• Reduced engine power or automatic derate mode, limiting machine performance to prevent further damage
• Erratic gauge readings or complete loss of display functions, including fuel level, temperature, and hour meter
• Intermittent starting issues or unexpected engine shutdown during operation
• Hydraulic system irregularities due to loss of communication between engine and hydraulic controllers

Potential Causes

The most common technical causes for Code P820 on used Sany excavators include:

Corroded or damaged CAN bus connectors – Moisture intrusion at connection points behind the cab or near the engine compartment is extremely common in aging machines, causing resistance spikes and communication dropouts.

Frayed or pinched wiring harness – The main engine harness often experiences wear at routing points near the swing bearing, boom pivot, or engine mounts where vibration and movement cause insulation breakdown.

Failed engine control module (ECM) – Internal component failure within the ECM itself, particularly in high-hour machines or those exposed to extreme temperatures and moisture.

Faulty termination resistors – The CAN bus network requires proper 120-ohm terminating resistors at each end; corrosion or failure of these resistors disrupts the entire communication protocol.

Voltage supply issues – Low battery voltage, failing alternator, or poor ground connections can cause the ECM to malfunction and trigger P820.

How to Troubleshoot and Fix Code P820

Step 1: Visual Inspection and Voltage Check

Begin with a thorough visual inspection of all wiring harnesses from the ECM to other control modules. On used excavators, pay special attention to harness routing where cables pass through metal grommets or near moving components. Check for abraded insulation, crushed wires, or signs of rodent damage. Using a digital multimeter, verify battery voltage is 12.5-13V (key off) and 13.8-14.4V (engine running). Inspect all ground connections at the ECM, battery, and frame grounds for corrosion or looseness.

Step 2: CAN Bus Network Testing

With the key on and engine off, use a multimeter to measure CAN bus resistance between the CAN-High and CAN-Low terminals at the ECM connector (consult Sany wiring diagrams for specific pin locations). You should read approximately 60 ohms with all modules connected, indicating proper termination. An open circuit (infinite resistance) suggests broken wiring or failed termination resistors. Inspect all CAN bus connectors for corrosion, bent pins, or moisture—clean with electrical contact cleaner and apply dielectric grease.

Step 3: ECM and Diagnostic Software Analysis

Connect Sany diagnostic software (or compatible heavy equipment scan tool) to retrieve detailed fault data and check for additional stored codes. Monitor live CAN bus communication status while wiggling harness connections to identify intermittent faults. If wiring and connections test properly, the ECM may have internal failure. Before replacing the ECM (a costly repair), verify power supply circuits provide clean 12V to all ECM pins and check for aftermarket accessories that may cause electrical interference.

For used excavators specifically, replace any corroded connectors rather than attempting repairs, as weakened connection integrity will cause recurring issues.

Disclaimer: This guide provides general troubleshooting information. Always consult the official Sany service manual for your specific model and serial number. Complex electrical diagnostics should be performed by qualified technicians with proper diagnostic equipment to avoid misdiagnosis and unnecessary part replacement.