Why Fault Codes Lie (And How Blindly Trusting Them Destroys Good Excavator Components)

RALPH COPE
2 minutes ago
5 min read

Modern excavators are smart.Too smart, sometimes.

They monitor themselves constantly, record abnormalities, and report faults through neatly packaged error codes. For many technicians and owners, those codes have become gospel.

And that’s the problem.

Fault codes do not diagnose failures.They report what the control system thinks is wrong — based on incomplete, indirect, and sometimes misleading information.

This blog explains why fault codes lie, how they mislead even experienced technicians, and how trusting them blindly results in unnecessary pump replacements, scrapped valve banks, and repeat failures — especially on modern Volvo, Komatsu, Hyundai, and Doosan machines.

What a Fault Code Really Is (And What It Isn’t)

A fault code is not a conclusion.It’s a symptom description.

The ECU is not saying:

“This part is broken.”

It is saying:

“This signal is not what I expected.”

That distinction matters more than most people realise.

Fault codes are triggered when:

A signal is out of range
A response is slower than expected
Communication is interrupted
A value conflicts with another input

None of those automatically mean the component named in the code has failed.

The ECU’s Biggest Limitation: It Can’t See Reality

An ECU:

Cannot feel pressure
Cannot hear cavitation
Cannot see contamination
Cannot measure mechanical wear

It only knows voltage, resistance, frequency, and logic.

If those inputs are wrong — even slightly — the ECU will make perfectly logical decisions based on bad information.

That’s how fault codes become convincing liars.

The Classic Trap: “The Code Says It’s the Pump”

Few phrases cost more money in excavator repair than:

“The code points to the pump.”

Here’s what’s really happening.

The ECU sees:

Low pressure signal
Or delayed pressure rise
Or unexpected load condition

So it flags:

Pump control fault
Pump pressure abnormal
Pump response error

But the real cause could be:

A drifting pressure sensor
Voltage drop to a solenoid
Internal valve leakage
CAN communication delay

The pump gets blamed because it’s downstream of the bad information.

Why Fault Codes Are Especially Dangerous on Modern Machines

Modern excavators are managed machines. Electronics decide:

Pump displacement
Engine power
Valve timing
Travel logic

This means:

One bad input can cripple the entire system
One electrical fault can mimic five mechanical failures

Older machines failed honestly.Modern machines fail plausibly.

False Positives: When Nothing Is Actually Broken

A false positive fault code is one of the most common — and expensive — diagnostic failures.

Common Causes of False Positives

Sensor signal drift
Heat-related resistance change
Intermittent wiring breaks
Ground instability
CAN bus noise

The ECU detects inconsistency and raises a fault — even though the component still works.

The result?

Parts get replaced unnecessarily
The real fault remains
The code comes back

And confidence erodes.

Pressure Sensors: Professional Liars

Pressure sensors are among the most misleading components in modern excavators.

They often:

Read plausibly wrong
Drift gradually
Fail only when hot
Stabilise when restarted

A pressure sensor that reads 20–30 bar low may:

Cause pump derating
Limit engine power
Trigger overload protection

The fault code will point to:

Pump performance
Hydraulic inefficiency
Load-sense error

When the pump is perfectly healthy.

RPM Sensors: Creating Mechanical Ghosts

A failing RPM sensor can:

Misreport engine speed
Desynchronise pump control
Trigger torque limits

The ECU responds by:

Reducing fuel
Limiting pump stroke
Activating protection modes

The machine feels:

Weak
Sluggish
Inconsistent

Fault codes may suggest:

Fuel issues
Turbo problems
Hydraulic overload

In reality, the ECU simply doesn’t trust the RPM signal.

Solenoids: Blamed for Power Problems They Didn’t Cause

Solenoids are often replaced because:

A code says “solenoid malfunction”
Resistance checks “seem off”
The function behaves inconsistently

But solenoids usually fail in only three ways:

Open circuit
Short circuit
Mechanical sticking

What they don’t do is partially fail gracefully.

If a solenoid is being blamed for:

Weak hydraulics
Slow response
Heat buildup

The real culprit is often:

Voltage drop
Poor grounding
Signal interference

The solenoid is innocent — but convicted.

CAN Bus Errors: Where Chaos Pretends to Be Logic

CAN bus systems allow multiple controllers to communicate on shared lines. When CAN goes wrong, everything looks broken.

CAN Bus Fault Symptoms

Multiple unrelated fault codes
Intermittent shutdowns
Communication timeouts
Random derates

The ECU flags whichever component failed to report correctly — not the wiring or network that caused the failure.

This leads to:

Sensor replacement
ECU replacement
Display replacement

While the real problem is a damaged loom or corroded connector.

Why Replacing the “Coded” Part Often Makes Things Worse

When you replace a component based only on a fault code:

The original fault often remains
The system resets temporarily
The machine appears fixed

Until:

Heat builds
Vibration increases
The same signal fails again

Now you have:

New parts
Old problems
Less diagnostic clarity

And a customer who doesn’t trust anyone anymore.

Fault Code Cascades: One Lie Creates Ten More

One incorrect input can cause a cascade of secondary fault codes.

For example:

A bad pressure sensor causes pump derate
Reduced pump output causes low flow
Low flow triggers valve response errors
Engine load mismatch triggers RPM faults

By the time diagnostics start, the machine shows:

Five active codes
Across three systems
All pointing in different directions

Only one thing is actually wrong.

Why Clearing Codes Is Not Diagnostics

Clearing fault codes does not:

Fix problems
Confirm repairs
Prove component health

It only resets the ECU’s memory.

If the fault returns:

It wasn’t fixed
It was masked

Professionals recreate faults under controlled conditions instead of clearing them and hoping.

The Correct Way to Use Fault Codes

Fault codes should be treated as:

Clues
Starting points
Symptom descriptions

They tell you:

Where the ECU noticed something wrong
Under what conditions
How often

They do not tell you:

Why it happened
What failed mechanically
Which part to replace

The Professional Diagnostic Order (Always)

Real diagnostics follow this order:

Power supply verification
Ground integrity testing
Wiring continuity and insulation
Signal verification with known-good references
Component testing
ECU replacement (rarely)

Skipping steps creates lies that look like logic.

Why Fault Codes Kill Good Hydraulic Parts

When electrical faults aren’t understood:

Pumps get blamed for derates
Valve banks get scrapped
Travel motors get replaced

But the real problem is upstream.

Electrical lies destroy hydraulic truth.

Brand Reality: Why Some Machines Are Worse Than Others

Volvo: Highly protective logic — derates early and often
Komatsu: Complex logic trees — one bad input triggers many codes
Hyundai: Cost-sensitive electronics — more signal drift
Doosan: Robust hydraulics masked by weak electrical connections

Different brands lie differently — but they all lie.

The Vikfin Position on Fault Codes

At Vikfin, we see the damage:

Good parts replaced
New components killed
Repeat failures blamed on “bad parts”

When the real issue was never mechanical.

We don’t sell parts based on codes.We sell parts based on evidence.

Final Truth

Fault codes are not evil.They’re just misunderstood.

They don’t tell you what failed.They tell you what the ECU didn’t like.

If you treat fault codes as verdicts, you will:

Replace good parts
Miss real faults
Spend more than necessary

If you treat them as clues, you become dangerous — in a good way.

Final Takeaway

Fault codes don’t lie maliciously.They lie logically.

And logic built on bad inputs is still wrong.

Diagnostics isn’t about reading codes.It’s about proving truth.

That’s how machines stay alive — and reputations intact.