Komatsu PC70-8 Fault Code DHSBMA: Complete Diagnostic Guide

What is Komatsu PC70-8 Fault Code DHSBMA?

Fault Code DHSBMA indicates a communication error or data transmission failure within the machine's hydraulic system monitoring network, specifically related to the hydraulic sensor bus or main controller area network (CAN) communication.

This code typically appears when the Electronic Control Module (ECM) cannot properly receive or interpret signals from one or more hydraulic system sensors on the PC70-8. The Komatsu PC70-8's integrated monitoring system relies on continuous data exchange between the main controller, hydraulic pressure sensors, and temperature monitoring circuits. When this communication breaks down, the machine cannot accurately regulate hydraulic functions, potentially leading to reduced performance or safety concerns. For used excavators, this fault often stems from age-related wiring degradation rather than component failure.

Common Symptoms

When DHSBMA is active on your PC70-8, operators typically experience:

• Warning light illumination on the instrument panel, often accompanied by a buzzer alert
• Reduced hydraulic response or sluggish boom/arm/bucket movements
• Intermittent loss of auxiliary hydraulic functions (breaker circuits, thumb controls)
• Erratic gauge readings for hydraulic oil temperature or pressure
• Engine derate mode in severe cases, limiting RPM to protect the system

Potential Causes

The most common technical causes for DHSBMA on used PC70-8 excavators include:

• Corroded or loose connector pins at the main hydraulic sensor harness (located near the hydraulic pump)
• Damaged CAN bus wiring due to rubbing against the boom cylinder or frame rails—a known wear point on this model
• Failed hydraulic pressure sensor (typically the main system pressure transducer)
• Water intrusion into the ECM connector or sensor junction box
• Faulty ECM ground connection causing voltage reference issues
• Aftermarket component interference from non-OEM sensors or poorly installed attachments

How to Troubleshoot and Fix Code DHSBMA

Step 1: Visual Inspection Begin by inspecting all hydraulic sensor harnesses from the pump area to the ECM. On used PC70-8s, check for wire chafing where the harness passes near the swing bearing and along the boom base. Look for corroded connectors, damaged insulation, or oil contamination on wiring.

Step 2: Connector Testing Disconnect the main hydraulic sensor connector (typically a 12-pin gray connector near the control valve). Use a multimeter to check for continuity on each pin to the ECM. Resistance should be less than 5 ohms. Clean all connector pins with electrical contact cleaner and apply dielectric grease before reconnecting.

Step 3: Sensor Voltage Verification Using Komatsu diagnostic software (KOMTRAX) or a compatible CAN bus scanner, monitor live data from hydraulic sensors. The main pressure sensor should output 0.5-4.5V depending on system pressure. Out-of-range readings indicate sensor failure.

Step 4: CAN Bus Integrity Check Measure CAN-High and CAN-Low voltage at the ECM connector (typically pins 6 and 14). You should see approximately 2.5V at rest, with 1V differential during communication. Significant deviation suggests wiring shorts or termination resistor failure.

Step 5: Component Replacement If diagnostics isolate a failed hydraulic pressure sensor, replace with genuine Komatsu parts (part number varies by serial number). For used machines, always replace the connector pigtail simultaneously, as internal corrosion often remains hidden.

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Disclaimer: This guide provides general diagnostic information. Always consult the official Komatsu PC70-8 service manual and consider professional assistance for complex electrical diagnostics. Improper repairs may void warranties or create safety hazards.