What is Sany Excavator Fault Code P958?

Fault Code P958 indicates a malfunction in the hydraulic pump pressure sensor circuit or an abnormal pressure reading detected by the ECM (Engine Control Module). This code specifically relates to the main hydraulic pump system's pressure monitoring circuit, which is critical for maintaining optimal hydraulic performance and protecting the system from over-pressurization or inadequate flow conditions.

In Sany excavators, the hydraulic pump pressure sensor continuously monitors system pressure and sends voltage signals to the ECM. When the sensor voltage falls outside the manufacturer's specified range (typically 0.5-4.5V), or when pressure readings are implausible for current operating conditions, the ECM triggers P958. This fault compromises the machine's ability to regulate hydraulic functions effectively, potentially leading to reduced cycle times, erratic boom/arm movement, or protective derate modes that limit operational capacity.

Common Symptoms

• Warning lamp illumination on the instrument cluster, often accompanied by a hydraulic system malfunction indicator
• Reduced hydraulic power or sluggish operation of boom, arm, bucket, or swing functions
• Intermittent loss of hydraulic response, particularly during high-demand operations like digging or lifting
• Engine derate mode activation, limiting RPM to protect hydraulic components from damage
• Erratic hydraulic function behavior, such as inconsistent swing speed or jerky movements

Potential Causes

The most common technical causes for P958 in used Sany excavators include:

• Failed hydraulic pump pressure sensor due to internal component wear or contamination from hydraulic fluid degradation
• Damaged or corroded wiring harness at connector points, especially where the harness routes near the hydraulic pump (a known rub point on older machines)
• Contaminated hydraulic oil causing sensor membrane damage or inaccurate readings
• Loose or corroded electrical connections at the sensor connector or ECM terminals
• ECM software calibration issues or internal ECM faults (less common but possible in high-hour machines)
• Actual hydraulic system pressure problems such as worn pump components, relief valve malfunction, or clogged filters

How to Troubleshoot and Fix Code P958

Step 1: Visual Inspection Begin by locating the hydraulic pump pressure sensor (typically mounted directly on the main hydraulic pump body). Inspect the sensor connector for corrosion, oil contamination, or loose pins. Check the wiring harness for abrasion, especially where it contacts the pump housing or frame—a common wear point in used excavators.

Step 2: Electrical Testing Using a digital multimeter, perform voltage and resistance checks. With the ignition on but engine off, backprobe the sensor connector to verify supply voltage (should read approximately 5V from the ECM). Check sensor ground continuity to the ECM (should read less than 1 ohm). Measure sensor signal voltage while manually creating pressure changes; it should vary smoothly between 0.5-4.5V.

Step 3: Hydraulic System Verification Connect Sany-specific diagnostic software (such as Sany Service Master) to monitor real-time pressure values. Compare actual hydraulic pressure (measured with a mechanical gauge at a test port) against sensor readings. A discrepancy indicates sensor failure. Also check hydraulic oil condition—contaminated or degraded oil can damage sensor membranes.

Step 4: Component Replacement and Calibration If electrical tests pass but readings remain incorrect, replace the pressure sensor using OEM or quality aftermarket parts. After replacement, clear fault codes and perform ECM relearning procedures per Sany service protocols. For used machines, always replace connector seals 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 serial number. Complex hydraulic or electrical diagnostics should be performed by qualified technicians with proper training and equipment.