Komatsu PC138USLC-8 Fault Code DHSJMA: Complete Diagnostic Guide

What is Komatsu PC138USLC-8 Fault Code DHSJMA?

Fault Code DHSJMA indicates a communication error between the Engine Control Module (ECM) and the Hydraulic System Controller on the Komatsu PC138USLC-8 excavator. This diagnostic trouble code specifically relates to a CAN bus communication failure or data transmission interruption within the machine's integrated control network.

This code is critical because the PC138USLC-8 relies on continuous data exchange between the ECM and hydraulic controllers to optimize fuel efficiency, engine performance, and hydraulic response. When communication breaks down, the machine may enter a protective derate mode to prevent potential damage, significantly impacting productivity on the jobsite.

Common Symptoms

When fault code DHSJMA is active, operators typically experience:

• Warning light illumination on the instrument cluster, often accompanied by a master caution indicator
• Reduced engine power or sluggish hydraulic response due to safety derate protocols
• Intermittent loss of auxiliary hydraulic functions or erratic boom/bucket movements
• Error messages displayed on the multi-function monitor indicating communication faults
• Engine stalling or rough idling during startup or under load conditions

Potential Causes

The most common technical causes for DHSJMA on used PC138USLC-8 excavators include:

• Damaged or corroded CAN bus wiring harness, particularly at known rub points near the engine mounting brackets and along the upper structure rotation path
• Faulty connector pins at the ECM or hydraulic controller due to moisture intrusion or vibration wear
• Failed termination resistors within the CAN network causing signal reflection and data corruption
• ECM or hydraulic controller software corruption from voltage spikes during jump-starting or electrical system repairs
• Grounding issues at the main chassis ground points, especially common in machines operating in wet or corrosive environments
• Worn connector seals allowing water and debris penetration—a frequent issue in high-hour used excavators

How to Troubleshoot and Fix Code DHSJMA

Step 1: Visual Inspection Begin by thoroughly inspecting the main wiring harness running between the ECM (located behind the operator cab) and the hydraulic pump controller. Check for visible damage, pinched wires, or areas where the harness contacts metal surfaces. On used excavators, pay special attention to connector corrosion and damaged weatherpack seals.

Step 2: CAN Bus Voltage Testing Using a digital multimeter, measure the CAN-High and CAN-Low voltage at the diagnostic connector. You should see approximately 2.5V on each line with the key on, engine off. Check for 120-ohm resistance between CAN-High and CAN-Low with the system powered down—this confirms proper termination resistor function.

Step 3: Connector Pin Inspection Disconnect the 20-pin ECM connector and hydraulic controller connector. Inspect each pin for bent terminals, green corrosion, or burnt contacts. Clean connections with electrical contact cleaner and apply dielectric grease to prevent future moisture issues—critical for used machines with years of environmental exposure.

Step 4: Software and Ground Verification Connect Komatsu KOMTRAX diagnostic software or an aftermarket scan tool to check for additional stored codes and verify ECM/controller software versions. Inspect and clean all chassis ground points, particularly ground G101 near the battery tray, as poor grounding frequently causes intermittent communication faults.

Step 5: Component Replacement If diagnostics point to a failed controller, verify the issue by swapping with a known-good unit when possible. For used excavators, replacing the entire wiring harness may be more cost-effective than repeated connector repairs if multiple rub-through points exist.

---

Disclaimer: This guide provides general diagnostic information for experienced technicians. Always consult the official Komatsu service manual for your specific machine serial number and software version. Complex electrical diagnostics should be performed by certified Komatsu technicians with proper diagnostic equipment to avoid costly misdiagnosis or additional damage.