Electrical Fault Diagnosis on the CAT CB24B Roller

[MikePhua]

CAT CB24B Overview
The Caterpillar CB24B is a compact tandem vibratory roller designed for asphalt compaction in urban and residential settings. Manufactured by Caterpillar, a global leader in construction equipment since 1925, the CB24B features a 47-inch drum width, a 24.8 hp diesel engine, and dual vibratory systems for efficient surface finishing. Its compact frame and intuitive controls make it ideal for tight job sites and patchwork operations. Caterpillar has sold thousands of CB24B units worldwide, with strong adoption in North America, Europe, and Southeast Asia.
Fuse Failure and Initial Troubleshooting
A recurring issue reported on the CB24B involves the F9 fuse—a 7.5-amp fuse located behind the dashboard—blowing immediately upon key activation. This points to a short circuit or overload condition in one of the circuits powered by the fuse. Initial diagnostics revealed that unplugging the ECU (Electronic Control Unit) prevented the fuse from blowing, suggesting the fault was downstream of the ECU or within its connected wiring.
Upon further inspection, five wires were found chafed and shorted against hydraulic hoses near the fuel tank fill area. These wires included:

• Purple 614-H10
  
• Yellow A364-H29
  
• Pink 151-H47
  
• Blue 159-H45
  
• Green P878-H15
  

These wire codes correspond to various sensor and control circuits, including fuel pump activation, hydraulic feedback, and ECU communication. Repairing the wires did not resolve the fuse issue, indicating possible ECU damage from the short.
ECU Diagnosis and Replacement
After restoring the wiring, the machine continued to blow the F9 fuse when both ECU connectors were plugged in. This behavior strongly suggests internal ECU failure, likely caused by voltage spikes or sustained shorts during operation. The machine could crank but failed to power the fuel pump, confirming that the ECU was not energizing the second half of the fuse box.
Diagnostic code MID039 CID0247 FMI09 was retrieved, pointing to a fault in the fuel pump circuit. Caterpillar confirmed the ECU was damaged and required replacement. Unfortunately, the only available unit was located in Belgium, with an estimated delivery time of 4–6 weeks.
Temporary Workaround and Field Advice
While waiting for the replacement ECU, technicians suggested a temporary workaround: tying the affected fuse box circuit to the functioning side using a properly rated inline fuse. This method allows limited operation without compromising safety, provided the load is within acceptable limits.
In similar cases, contractors have used this method to keep rollers operational during peak paving season. One firm in Ontario rerouted power to the fuel pump using a fused jumper and completed a municipal road contract without delay.
Recommendations for Preventing Electrical Damage

• Secure wire harnesses away from moving hydraulic components
  
• Use abrasion-resistant sleeves in high-friction zones
  
• Inspect fuse boxes monthly for signs of heat or corrosion
  
• Log fault codes and voltage readings during diagnostics
  
• Keep printed wiring diagrams on-site for quick reference
  

A technician in Connecticut printed the CB24B wiring diagram on a 4x3-foot jobsite plotter, allowing easy tracing of wire numbers and connections. This visual aid accelerated troubleshooting and reduced downtime.
Conclusion
Electrical faults in the CAT CB24B, especially involving the ECU and fuel pump circuits, can be traced to wire abrasion and shorting. While repairs may require ECU replacement, temporary solutions and methodical diagnostics can restore partial functionality. With proper harness protection and regular inspection, operators can prevent similar failures and maintain reliable compaction performance.