CAT 933 No Start, Breaker Blows: Troubleshooting and Solutions

[MikePhua]

The Caterpillar 933, a compact track loader used in various construction, agricultural, and landscaping applications, is known for its durability and versatility. However, like all heavy equipment, it can experience issues that prevent it from starting or operating correctly. One such problem involves the machine not starting and the breaker continuously blowing, which can be frustrating and lead to costly downtime. In this guide, we'll walk through common causes of this issue, provide troubleshooting steps, and offer potential solutions to restore the CAT 933 to full working order.
Understanding the Problem: No Start and Breaker Blowing
When the CAT 933 fails to start, and the breaker keeps blowing, it typically points to an electrical issue that causes an overload or short circuit in the system. The breaker is designed to protect the electrical system from excessive current, so if it's blowing, it means there’s a fault in the circuit that needs to be addressed before further attempts to start the machine.
Common Causes of a Blown Breaker and No Start Issue
Several factors could cause this problem, ranging from a faulty electrical component to a wiring issue. Below are some common causes of the no-start and breaker-blowing problem:

1. Short Circuit in the Electrical System
   • A short circuit can occur when electrical wiring comes into contact with a metal surface or if insulation on the wires has worn out. This can lead to an electrical surge that trips the breaker.
     
   • Symptoms: The breaker blows immediately when the machine is turned on.
     
   • Solution: Inspect all wiring, particularly near areas of high movement or where wires may rub against metal surfaces. Check for exposed wires and replace any damaged wiring. Ensure all connectors are tight and free of corrosion.
     
2. Faulty Starter Motor or Solenoid
   • The starter motor is responsible for turning over the engine. If the starter motor or its solenoid fails, it can cause an electrical overload, tripping the breaker.
     
   • Symptoms: The engine doesn’t crank, and the breaker blows after turning the key.
     
   • Solution: Test the starter motor and solenoid with a multimeter. If the solenoid is faulty or the motor is drawing excessive current, replace them. In some cases, cleaning the solenoid contacts can resolve the issue.
     
3. Blown Fuses or Relays
   • If a fuse or relay has blown, it can cause an electrical imbalance that trips the breaker. This can happen if there is a sudden surge of current when trying to start the machine.
     
   • Symptoms: The breaker trips, and you notice that a fuse or relay is blown.
     
   • Solution: Inspect all fuses and relays in the electrical system. Replace any that are blown and check for any obvious issues with the electrical circuit that could cause repeated blowouts.
     
4. Overloaded or Faulty Alternator
   • A faulty alternator can cause excessive current to flow through the electrical system, leading to breaker tripping. If the alternator is producing too much voltage, it can damage sensitive electrical components and cause a short circuit.
     
   • Symptoms: The machine starts, but the breaker trips after running for a short period.
     
   • Solution: Test the alternator using a voltmeter to ensure it’s charging the system properly. If the alternator is faulty, it may need to be replaced.
     
5. Damaged Battery Cables or Connectors
   • Corroded or damaged battery cables can create resistance in the circuit, leading to an overload when starting the machine. Poor connections can also cause electrical arcing that can trip the breaker.
     
   • Symptoms: The engine doesn’t crank, or there’s a delay before the machine starts, followed by the breaker blowing.
     
   • Solution: Inspect the battery cables and connectors for corrosion, wear, or loose connections. Clean the battery terminals and ensure all connections are tight and free from dirt or debris.
     

Troubleshooting Steps
If you’re facing a no-start situation with a tripping breaker, follow these troubleshooting steps to identify and resolve the issue:

1. Check the Breaker: Start by inspecting the breaker itself. Sometimes, the breaker may be faulty and trip even without an actual overload. Replace the breaker if necessary.
   
2. Inspect Electrical Wiring: Visually check all wiring for signs of damage or wear. Look for exposed wires, burnt areas, or places where wires may be rubbing against sharp edges or metal components.
   
3. Test the Starter Motor and Solenoid: Use a multimeter to check if the starter motor is drawing excessive current. Inspect the solenoid for proper operation.
   
4. Check Fuses and Relays: Look for any blown fuses or damaged relays and replace them. Ensure that the fuses and relays are the correct rating for the electrical components they protect.
   
5. Test the Alternator: Check the alternator output with a voltmeter to ensure it's charging correctly. If the voltage is too high or low, replace the alternator.
   
6. Inspect Battery Connections: Clean and tighten the battery terminals. If the cables are corroded or damaged, replace them.
   

Real-World Example: CAT 933 Troubleshooting Case
In a real-world case, a contractor in California faced issues with his CAT 933 when it would not start, and the breaker would blow immediately after turning the key. After troubleshooting the electrical system, it was found that the starter motor was drawing excessive current, causing an overload in the circuit. By replacing the faulty starter motor and cleaning the battery terminals, the problem was resolved, and the machine returned to service without further electrical issues.
Conclusion
If your CAT 933 is experiencing a no-start condition and the breaker keeps blowing, it is likely due to an electrical fault, such as a short circuit, faulty starter motor, or damaged wiring. By following the troubleshooting steps outlined above, you can identify the root cause of the issue and take the necessary steps to restore the machine to full operation. Regular maintenance, including inspecting electrical components and ensuring proper wiring, will help prevent these types of problems from occurring in the future.