Modern construction machinery HMIs are no longer just digital dashboards. In excavators, wheel loaders, mining trucks, sprayers, and sanitation vehicles, the HMI has become the center of machine interaction, diagnostics, and operational safety.

However, many OEMs still make one major mistake:

They display the same fault information to both operators and service technicians.

In reality, these two users need completely different information.

• Operators need fast decisions.

• Technicians need deep diagnostics.

A well-designed HMI should separate these two roles through different fault display layers: Operator View and Service View.

Why Fault Display Logic Matters

Construction machinery operates in harsh environments:

• Dust

• Vibration

• Noise

• Long working hours

• High operator fatigue

When a fault occurs, the operator usually needs immediate guidance, not engineering-level diagnostic data.

For example, showing this on the main screen:

SPN 110 FMI 1

may technically be correct, but it is not useful for most operators.

A better operator-facing message would be:

Engine Coolant Temperature High
Reduce Engine Load

This tells the operator:

• What happened

• How serious it is

• What action to take

That is the real purpose of operator view.

What Is Operator View?

Operator view is the fault display interface designed for machine operators during daily work.

Its primary goals are:

• Safety

• Fast readability

• Reduced distraction

• Clear actions

The operator does not need to understand:

• CAN topology

• Sensor voltage

• SPN/FMI structure

• ECU communication logic

Instead, operators need simple and actionable information.

Information Typically Shown in Operator View

Most construction machinery HMIs display:

• Engine RPM

• Hydraulic pressure

• Coolant temperature

• Fuel level

• Machine mode

• Attachment status

• Safety alarms

• Warning indicators

The fault display system should remain simple and easy to understand even under difficult conditions such as sunlight, vibration, or glove operation.

Fault Severity Logic in Operator View

Most modern HMIs divide faults into three levels.

This is far more effective than displaying raw diagnostic codes.

The operator only needs to know:

1. Can I continue operating?

2. Which system is affected?

3. What should I do now?

What Should Not Be Shown to Operators

One of the biggest HMI design mistakes is exposing raw diagnostic data directly on the operator screen.

Examples include:

• SPN

• FMI

• PGN

• Hex CAN errors

• ECU IDs

These values are useful for technicians, but often meaningless to operators.

In real-world projects, operators frequently ignore these alarms because they cannot translate them into actions.

This can lead to:

• Delayed reactions

• Machine damage

• Increased downtime

• Safety risks

What Is Service View?

Service view is designed for:

• Maintenance engineers

• OEM support teams

• Diagnostic technicians

• After-sales personnel

Unlike operator view, service view should expose deeper system-level information.

Its purpose is troubleshooting.

Information Typically Shown in Service View

A good service view usually includes:

• SPN/FMI

• PGN data

• ECU communication status

• Sensor values

• CAN bus diagnostics

• Fault history

• Timestamps

• Fault occurrence count

• Active/stored fault distinction

This allows technicians to identify root causes much faster.

Why SPN and FMI Matter in Service View

Most off-highway machinery uses SAE J1939 diagnostics.

J1939 faults are commonly represented using:

• SPN (Suspect Parameter Number)

• FMI (Failure Mode Identifier)

For example:

FMI then defines the failure condition.

This information is extremely valuable for technicians but should usually remain inside the service layer instead of the operator layer.

Active Fault vs Historical Fault

A good HMI should clearly separate:

• Active faults

• Historical faults

• Intermittent faults

Many poorly designed HMIs mix them together.

This creates confusion because operators may think an old stored fault is still active.

A better structure is:

Operator View vs Service View

Example: Hydraulic Pressure Fault

Poor HMI Design

Operator sees:

SPN 108 FMI 3

The operator does not know:

• What failed

• Whether operation is safe

• What action to take

Better Operator View

Hydraulic Pressure Abnormal
Reduce Attachment Load

Simple and actionable.

Better Service View

Now the technician has enough information to diagnose the issue efficiently.

Common HMI Design Mistakes

1.Showing Raw Diagnostic Codes to Operators

SPN/FMI codes are designed for diagnostics, not machine operation.

2. Treating All Faults Equally

A low DEF warning should not behave like:

• Brake failure

• Hydraulic overpressure

• Engine shutdown

Fault priority matters.

3. Mixing Active and Historical Faults

Stored faults should not appear like active faults.

4. Overloading the Main Screen

Too many alarms reduce operator attention and increase stress.

The HMI should prioritize only the most important information.

Recommended Fault Display Architecture

A modern construction machinery HMI should separate fault information into different layers.

Operator Layer

Focus on:

• Safety

• Immediate actions

• Simple warnings

• Machine status

Service Layer

Focus on:

• Diagnostics

• Root cause analysis

• CAN/J1939 data

• Sensor monitoring

• Fault history

Engineering Layer (Optional)

Advanced systems may also include:

• Calibration tools

• ECU configuration

• CAN analysis

• Software update tools

Usually protected by passwords.

Conclusion

The best HMIs do not simply display more information.

They display the right information to the right user.

Operators need decisions.
Technicians need details.

A clear separation between Operator View and Service View improves:

• Safety

• Troubleshooting efficiency

• Operator usability

• Maintenance speed

• Machine uptime

As construction machinery becomes more connected and software-driven, fault display logic is becoming one of the most important parts of modern HMI design.