Modern mobile machinery depends on sensors to monitor pressure, temperature, position, speed, and other operating conditions.But what happens when a sensor fails?
A damaged cable, loose connector, short circuit, or faulty sensor can send incorrect information to the controller. If the control system treats that signal as valid, the machine may respond incorrectly.
For this reason, mobile controllers should not only read sensor signals—they should also determine whether those signals are reliable.
A typical fault detection process is:
Sensor
↓
Controller Input
↓
Signal Validation
↓
Fault Detection
↓
HMI Warning / Safe Action
Mobile machinery operates in environments with vibration, moisture, dust, temperature changes, and mechanical stress.
Common sensor-related failures include:
Broken wires
Loose or corroded connectors
Short circuits
Sensor power supply faults
Signal values outside the expected range
CAN communication loss
Internal sensor failure
The controller can use different diagnostic strategies to detect these problems.
An open circuit occurs when the electrical connection between the sensor and controller is interrupted.
Possible causes include:
Broken wiring
Disconnected connectors
Damaged terminals
Internal sensor failure
For example, if a pressure sensor normally outputs 0.5–4.5 V, a signal close to 0 V may indicate a wiring or sensor fault rather than simply zero pressure.
The controller software can define acceptable signal limits and generate a fault when the input remains outside that range.
Sensor wiring may also become shorted to ground or supply voltage.
For a 0–5 V sensor, an abnormal signal close to 0 V or 5 V may indicate a short circuit.
The controller can monitor these conditions and respond by:
Setting a diagnostic fault
Displaying a warning
Disabling the affected function
Switching to a predefined fallback value
The exact response depends on the machine and the importance of the sensor.
One of the simplest diagnostic methods is range checking.
Consider a sensor with a valid operating range of:
Normal Signal: 0.5–4.5 V
Below 0.5 V → Possible Fault
Above 4.5 V → Possible Fault
Similar strategies can be used for:
0–5 V sensors
0–10 V sensors
4–20 mA sensors
Resistive sensors
Using diagnostic ranges outside the normal measurement range helps the controller distinguish between a real operating condition and an electrical fault.
Sometimes a sensor signal remains within its electrical range but the value itself does not make sense.
For example, a position sensor may suddenly change from 20% to 90% within an unrealistically short time.
The controller can compare:
Current value
Previous value
Rate of change
Machine operating state
Related sensor values
This allows the software to identify implausible signals, not just electrical faults.
Not every sensor uses an analog input. Some intelligent sensors communicate through CAN or J1939.
In this case, the controller can monitor whether expected messages continue to arrive.
Normal Signal: 0.5–4.5 V
Below 0.5 V → Possible Fault
Above 4.5 V → Possible Fault
If the controller does not receive the expected message within a defined period, it can report a communication fault.
This is commonly known as timeout detection.
Some applications use two sensors to measure the same or related parameters.
The controller can compare both values:
Sensor A ──┐
├──→ Mobile Controller → Comparison
Sensor B ──┘
If the difference becomes greater than an allowed tolerance, the system can identify a possible sensor fault.
Redundant sensing may be useful in applications where reliable signal validation is particularly important.
Detecting a fault is only part of the process. The machine should also provide useful diagnostic information.
The controller can send fault information to the HMI through CAN.
The operator or service technician may then see information such as:
Pressure sensor fault
Signal out of range
CAN sensor communication lost
Temperature sensor disconnected
Position sensor mismatch
Clear diagnostic information can reduce troubleshooting time during machine maintenance.
The correct response depends on the function of the sensor.
For a non-critical sensor, the system may simply display a warning.
For a sensor involved in machine control, the controller may need to:
Disable an output
Limit hydraulic movement
Use a predefined fallback value
Reduce machine performance
Enter a safe operating mode
For example:
Pressure Sensor Fault
↓
Controller Detects Invalid Signal
↓
Fault Code + HMI Warning
↓
Affected Hydraulic Function Limited
Fault detection should therefore be considered together with the machine's overall control and safety strategy.
Consider a hydraulic system using a 0.5–4.5 V pressure sensor.
During normal operation:
Pressure Sensor
↓
0.5–4.5 V Signal
↓
Mobile Controller
↓
Hydraulic Control Logic
If the wiring breaks and the signal falls outside the expected range, the controller can recognize the input as invalid.
Instead of interpreting the signal as actual hydraulic pressure, it can generate a fault and apply the predefined control response.
This prevents an invalid sensor value from being treated as normal machine data.
When designing sensor diagnostics, OEM engineers should consider:
Normal signal range
Fault detection thresholds
Open-circuit behavior
Short-circuit behavior
CAN message timeout
Signal filtering
Rate-of-change limits
Fault delay time
Fault recovery conditions
Machine response after a fault
Diagnostics should be designed according to the characteristics of the sensor and the requirements of the machine.
Reliable mobile machinery control requires more than simply reading sensor values.
Controllers should also detect open circuits, short circuits, out-of-range values, implausible signals, and communication failures.
By combining signal validation with diagnostic codes, HMI warnings, and appropriate fallback strategies, OEMs can improve machine reliability and make troubleshooting easier.
SonnePower provides programmable mobile controllers, HMI displays, remote I/O modules, and customized control solutions for mobile machinery.
With flexible analog, digital, CAN, J1939, and CANopen interfaces, SonnePower controllers can support sensor monitoring, fault detection, diagnostics, and machine control for construction, agricultural, mining, and other mobile equipment.
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