Why a 2005 Doosan Solar 225LC‑V Stalls When Boom or Stick Is Held Against Relief

[MikePhua]

Machine and Problem Overview
A 2005 Doosan Solar 225LC‑V may stall when the boom or stick is held hard against the relief valve—even at full engine RPM. Interestingly, bucket dump/curl functions operate normally, and travel works fine while other circuits are running. The stall occurs whether the machine is cold or hot and typically only when the boom or stick is hydraulically overloaded.
Typical Symptoms Reported
• Boom or stick held against relief causes engine stall at full RPM
• Bucket functions operate without issue
• Travel movement fine even when operating other hydraulic functions
• Stall occurs regardless of ambient temperature
• Hydraulics are adequate until cylinder meets relief stop
Likely Causes Behind the Stall
Analysis and field experience suggest these root causes:
• Torque‑limiter / pump control fault: The machine may be operating with its pump’s proportional pressure reducing (EPPR) solenoid inactive or stuck—causing pressure demand to exceed engine capability, stalling the engine under high hydraulic load. Similar machines exhibit this symptom when the solenoid lacks power or sticks internally .
• Engine control or throttle response issue: Fault codes like “TPS open” (23N) indicate that the throttle position or pump pilot control isn’t regulating engine RPM as required, affecting performance under heavy loads .
• Fuel or engine power limitation: Although less likely given the symptom profile, clogged filters or engine power loss can contribute to bogging during high flow demand .
Diagnostic Approach
A structured approach includes:
• Monitor pump pressures via EPOS display: Check front and rear pump pressures—stick and bucket relief pressures should be approximately 4785 psi ± 75 psi (check units: 1 bar ≈ 14.7 psi). Confirm only one function is operated at a time .
• Examine fault codes on display monitor: A code such as 23N (TPS open) frequently points to EPPR solenoid failure or throttle/pilot input errors .
• Test or bypass EPPR (proportioning) solenoid: The solenoid located on the main pump often is plug‑and‑play. Loss of current to this component or sticking internally leads to constant maximum torque demand and stalls .
• Switch to manual torque or backup mode (if available): In other excavator models this allows lesser pump output and avoids engine overload, which can indicate solenoid/controller fault .
Terminology Note
• EPPR (Electrical Proportional Pressure Reducing) Solenoid: Controls pilot pressure to limit pump torque demand.
• TPS (Throttle Position Sensor): Indicates throttle opening; a code like “TPS open” suggests full throttle without regulation.
• Torque Limiter Control: Prevents pump from overworking engine by limiting hydraulic torque.
• Pump‑to‑ECU communication (EPOS): Machine monitor shows pump pressures and engine/pump modes (e.g., digging vs standard mode).
Real‑World Field Story
A machine operator found that simple fuel filter servicing temporarily restored normal operation—pointing to possible engine load limitation. However, deeper analysis showed that a stale code (“TPS open”) and EPOS data pointed at the EPPR solenoid not functioning. Once replaced, the machine could hold boom or stick against relief without stall—even when the pump ran at full output.
In another case (similar model), a technician manually supplied current to the solenoid coil using bench parts to confirm that restoring pilot pressure prevented engine stalling—proving the solenoid wiring rather than hydraulic pump internals was at fault .
Troubleshooting Checklist (List Form)
• Verify display pump pressures and operating mode
• Scan or review historical/current fault codes (especially 23N)
• Locate and test the EPPR solenoid (check voltage and resistance)
• Try operating machine in backup/manual pump mode (if accessible)
• Inspect throttle linkage and engine governor if throttle codes present
• Service fuel filters, check fuel delivery, and ensure proper engine performance
Why This Matters
This stall condition isn’t typical of clogged valves or pump mechanical failure—and replacing the pump without testing solenoid or controller often wastes thousands of dollars. Diagnosing smartly—by checking the EPPR solenoid and control system—can resolve the issue quickly and economically.
Conclusion
If a 2005 Doosan Solar 225LC‑V stalls under booms or sticks held hard, even at full RPM, the likely culprit is a missing or faulty pump torque‑limiter control, typically the EPPR solenoid or its control voltage. Inspect pump pressure readouts, fault codes, and test/replace the solenoid before assuming engine or hydraulic pump failure. With proper diagnostics, the solution is often simple—and restores full function under heavy hydraulic load reliably and efficiently.