Brand-Specific Electrical vs Hydraulic Diagnostic Flow Charts - How Each Manufacturer Lies Differently (and How to Catch Them)

VOLVO EXCAVATORS

“If It Feels Weak, It’s Probably Being Told To”

Volvo Diagnostic Reality

Volvo machines are extremely protective.They derate early and aggressively based on sensor input.

Most “hydraulic failures” on Volvo are permission failures, not component failures.

VOLVO-SPECIFIC FLOW

STEP 1: UNDERPERFORMING MACHINE

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STEP 2: CHECK DERATE STATUS FIRST (NOT LAST)

• Engine torque limit active?

• Hydraulic power limit active?

➡️ If YES → STOP. Hydraulics are innocent.

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STEP 3: PRESSURE SENSOR VALIDATION (CRITICAL)

• Compare sensor reading vs mechanical gauge

• Watch for drift when hot

➡️ Sensor mismatch = fake hydraulic weakness

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STEP 4: COMMAND vs ACTUAL PUMP STROKE

• Volvo often limits pump stroke silently

➡️ Limited stroke with normal pressure capability = electrical control issue

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STEP 5: CASE DRAIN (ONLY AFTER ELECTRICAL CLEARED)

• High case drain = real wear

• Normal = stop blaming pump

VOLVO GOLDEN RULE

If a Volvo feels weak but sounds healthy, believe the electronics—not your hands.

KOMATSU EXCAVATORS

“One Bad Signal Creates Ten Fault Codes”

Komatsu Diagnostic Reality

Komatsu machines cascade faults.One incorrect input can trigger multiple unrelated error codes.

Technicians often replace everything except the cause.

KOMATSU-SPECIFIC FLOW

STEP 1: MULTIPLE FAULT CODES PRESENT?

⬇️➡️ YES = suspect ONE signal, not many failures

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STEP 2: VERIFY LOAD SENSE & PPC PRESSURES

• Komatsu load sense errors look like pump failure

➡️ Incorrect LS pressure = system confusion, not wear

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STEP 3: SENSOR VS MECHANICAL COMPARISON

• Komatsu ECUs trust sensors blindly

➡️ Bad sensor = entire machine derates

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STEP 4: ISOLATE BEFORE REPLACING

• Disable valve sections

• Block pilot circuits

➡️ Restoration of function = valve or signal issue

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STEP 5: CASE DRAIN CONFIRMATION

• Only condemn pump after LS & sensors cleared

KOMATSU GOLDEN RULE

Multiple fault codes usually mean one liar, not ten broken parts.

DOOSAN / DEVELON EXCAVATORS

“Strong Iron, Weak Signals”

Doosan Diagnostic Reality

Doosan hydraulics are tough.Wiring, connectors, and grounds are not.

Most Doosan “hydraulic failures” start as electrical supply problems.

DOOSAN-SPECIFIC FLOW

STEP 1: CHECK GROUNDS BEFORE ANYTHING

• Frame grounds

• ECU grounds

• Engine grounds

➡️ Poor ground = fake hydraulic failure

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STEP 2: SOLENOID VOLTAGE UNDER LOAD

• Doosan solenoids are sensitive to voltage drop

➡️ Low voltage = weak hydraulics illusion

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STEP 3: COMMAND STABILITY TEST

• Look for fluctuating duty cycles

➡️ Instability = electrical, not hydraulic

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STEP 4: HYDRAULIC PRESSURE TEST

• Doosan pumps rarely fail quietly

➡️ Low pressure with good electrics = real wear

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STEP 5: CASE DRAIN (CONFIRM ONLY)

• High = worn

• Normal = stop digging

DOOSAN GOLDEN RULE

If a Doosan hydraulic part failed, prove the electrics didn’t kill it first.

HYUNDAI EXCAVATORS

“Economical Electronics, Honest Hydraulics”

Hyundai Diagnostic Reality

Hyundai machines often suffer from:

• Sensor inconsistency

• Connector quality issues

• Voltage instability

Hydraulics get blamed because electronics fail subtly.

HYUNDAI-SPECIFIC FLOW

STEP 1: SENSOR PLAUSIBILITY CHECK

• Pressure sensors

• RPM sensors

• Temperature sensors

➡️ Inconsistent readings = derate logic triggered

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STEP 2: COMMAND LIMIT CHECK

• Hyundai will quietly limit output without shutdown

➡️ Limited command = electrical issue

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STEP 3: MECHANICAL PRESSURE CONFIRMATION

• Always verify with gauges

➡️ Normal pressure = hydraulics innocent

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STEP 4: VALVE RESPONSE TEST

• Delayed response often electrical, not mechanical

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STEP 5: CASE DRAIN ONLY IF PRESSURE IS LOW

• Don’t jump ahead

HYUNDAI GOLDEN RULE

Hyundai hydraulics don’t “fade.”Electronics quietly tell them to stop working.

CAT (BONUS)

“Electronics Are Honest—But Unforgiving”

CAT Diagnostic Reality

CAT systems are precise.They expect perfect data.

Small deviations cause big reactions.

CAT-SPECIFIC FLOW

STEP 1: DATA VALIDATION

• CAT hates borderline sensor values

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STEP 2: EVENT HISTORY REVIEW

• CAT logs problems before failure

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STEP 3: CONTROL PRESSURE STABILITY

• CAT reacts aggressively to instability

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STEP 4: COMPONENT REPLACEMENT ONLY AFTER CONFIRMATION

• CAT parts fail expensively when misdiagnosed

CAT GOLDEN RULE

CAT doesn’t guess.If it reacts, something upstream is wrong.

FINAL UNIVERSAL RULE (ALL BRANDS)

Measure pressure.Verify signal.Confirm case drain.Replace nothing on feel alone.