Electrical vs Hydraulic Misdiagnosis (How Excavators Trick You Into Replacing the Wrong Parts)

Modern excavators are excellent liars.

They can lose power, hesitate, overheat, derate, or behave erratically—while convincing even experienced technicians that the failure is hydraulic when it’s electrical… or electrical when it’s hydraulic.

The result?

• Good pumps replaced unnecessarily

• Valve banks scrapped prematurely

• Travel motors killed by bad signals

• Electrical faults chased with spanners

• Hydraulic faults chased with laptops

This blog explains why electrical and hydraulic failures masquerade as each other, how to tell them apart, and how to stop misdiagnosing modern excavators—especially Volvo, Komatsu, Hyundai, and Doosan machines.

Why Misdiagnosis Is Worse Than Failure

A broken machine costs money.

A misdiagnosed machine costs:

• Money

• Time

• Parts

• Trust

• Reputation

Misdiagnosis doesn’t fix the problem—it adds damage.

Most repeat failures are not bad parts.They’re bad decisions based on incomplete diagnostics.

The Root Problem: Managed Hydraulics

Older excavators were:

• Mechanically governed

• Hydraulically honest

Modern excavators are:

• Electronically managed

• Hydraulically obedient

Hydraulics no longer decide how much work they do.Electronics tell them.

That means:

• Electrical lies create hydraulic symptoms

• Hydraulic wear creates electrical reactions

If you don’t separate cause from reaction, you replace the wrong thing.

The Fundamental Diagnostic Question

Before touching a spanner or a laptop, ask this:

Is the machine unable to perform—or being told not to?

That question alone prevents most misdiagnoses.

How Electrical Faults Masquerade as Hydraulic Failures

Electrical faults don’t usually shut machines down completely.

They:

• Derate

• Limit

• Hesitate

• Protect

Which feels hydraulic.

Common Electrical Faults That Look Hydraulic

• Pressure sensor drift

• RPM sensor instability

• Voltage drop to solenoids

• CAN bus interference

• Poor grounding

The hydraulics are capable—but not allowed to work properly.

Example 1: “Weak Hydraulics” That Aren’t Weak

Symptoms

• Sluggish functions

• Poor multi-functioning

• Feels underpowered

• No obvious noise

Common Wrong Diagnosis

“Pump is tired.”

What’s Actually Happening

• Pressure sensor is under-reporting load

• ECU believes system is overloaded

• Pump stroke is limited electronically

The pump is healthy.The signal is lying.

Replacing the pump:

• Doesn’t fix the issue

• Introduces contamination risk

• Creates future failures

Example 2: Electrical Derate Disguised as Pump Failure

Symptoms

• Machine works cold, weak hot

• Loses power under load

• Improves after restart

Blamed Component

• Hydraulic pump

Real Cause

• Heat-affected sensor or wiring

• Resistance change when hot

• ECU enters protection mode

This failure pattern screams electrical, not hydraulic.

How Hydraulic Faults Masquerade as Electrical Failures

Hydraulic wear often causes:

• Slow response

• Pressure delays

• Heat buildup

Which the ECU detects as:

• Performance errors

• Response faults

• Control instability

The ECU flags electrical components because it doesn’t understand wear.

Example 3: Valve Leakage Creating Electrical Chaos

Symptoms

• Multiple fault codes

• Inconsistent performance

• Random derates

Blamed Components

• Sensors

• Solenoids

• ECU

Actual Fault

• Internal valve leakage

• Pressure instability

• Flow loss

The electronics are reacting correctly to bad hydraulics.

Replacing sensors only hides the problem temporarily.

The Pressure vs Signal Trap

Pressure and signal are not the same thing.

Scenario	Pressure	Signal
Healthy system	Correct	Correct
Electrical fault	Correct	Wrong
Hydraulic fault	Wrong	Correct
Chaos	Wrong	Wrong

If you don’t measure both, you guess.

Why Fault Codes Make Misdiagnosis Worse

Fault codes:

• Describe symptoms

• Name affected circuits

• Do not identify root cause

A hydraulic failure triggers electrical fault codes.An electrical failure triggers hydraulic behavior.

Codes are reaction logs, not verdicts.

The Misdiagnosis Feedback Loop

This is how good machines get destroyed:

1. Electrical fault limits hydraulics

2. Hydraulics feel weak

3. Pump is replaced

4. Electrical fault remains

5. New pump overheats or fails

6. “Bad part” gets blamed

The original fault was never mechanical.

Case Drain: The Great Truth Filter

Case drain testing is one of the few tools that cuts through misdiagnosis.

If case drain is:

• High → hydraulic wear

• Normal → stop blaming the pump

Normal case drain + weak machine = electrical or valve issue.

Skipping case drain is how pumps die innocent.

Solenoids: The Most Wrongly Accused Component

Solenoids are blamed for:

• Weak functions

• Delayed response

• Jerky movement

But solenoids rarely “half fail.”

If resistance is stable and voltage is correct:

• The solenoid is fine

• The command or hydraulic circuit is not

Voltage drop and grounding issues create hydraulic symptoms that look mechanical.

CAN Bus: Where Electrical Faults Pretend to Be Everything

CAN bus issues create:

• Multiple unrelated fault codes

• Intermittent shutdowns

• Random derates

These symptoms mimic:

• Pump failure

• Valve failure

• Engine failure

In reality, it’s often:

• One damaged wire

• One corroded connector

• One bad ground

Replacing components won’t fix a network problem.

Brand-Specific Misdiagnosis Patterns

VOLVO

• Aggressive protection logic

• Sensor drift causes early derates

• Hydraulics blamed unfairly

KOMATSU

• Complex load-sense logic

• One bad input creates fault cascades

• Electronics blamed for hydraulic wear—and vice versa

DOOSAN

• Tough hydraulics

• Vulnerable wiring and grounds

• Mechanical parts replaced unnecessarily

HYUNDAI

• Cost-effective electronics

• Sensor inconsistency

• Hydraulic components blamed too quickly

Each brand lies differently.Diagnostics must adapt.

The Correct Diagnostic Separation Process

Professionals separate systems before condemning parts.

Step 1: Verify Power and Grounds

Electrical lies start here.

Step 2: Verify Signals

Compare sensors to mechanical reality.

Step 3: Verify Pressure and Flow

Hydraulics don’t lie when measured correctly.

Step 4: Verify Case Drain

Confirms or clears pumps and motors.

Step 5: Isolate Functions

Valves reveal themselves when isolated.

Only after this do you replace components.

Why Replacing the Wrong Part Makes the Right Problem Worse

Replacing hydraulics without fixing electronics:

• Introduces new tolerances

• Raises system stress

• Shortens component life

Replacing electronics without fixing hydraulics:

• Masks wear

• Delays failure

• Creates unpredictable behavior

Misdiagnosis compounds damage.

The Vikfin Position on Misdiagnosis

At Vikfin, we see the aftermath:

• “Bad” pumps that were healthy

• “Faulty” valves that were fine

• “Electrical gremlins” caused by worn hydraulics

We don’t treat electrical and hydraulic systems as enemies.

They’re accomplices.

The Rule That Prevents 80% of Mistakes

If hydraulics are weak, prove they’re allowed to be strong.If electronics look wrong, prove the hydraulics are stable.

Never assume.

Final Truth

Electrical systems tell hydraulics what to do.Hydraulics tell electronics what happened.

If either lies, the other looks guilty.

Your job is to determine who started it.

Final Takeaway

Most excavator failures are not mysterious.They’re misunderstood.

Misdiagnosis happens when:

• Electronics are trusted blindly

• Hydraulics are judged by feel

• Pressure and signal aren’t compared

Separate the systems.Prove the truth.Replace only what’s guilty.

That’s how machines last—and reputations survive.