Troubleshooting a CAT 955L That Won’t Run: A Comprehensive Guide

[MikePhua]

Introduction
The Caterpillar 955L track loader is an essential piece of equipment for a wide variety of industries, including construction, mining, and demolition. However, like any piece of heavy machinery, it can experience issues from time to time. One of the most frustrating issues an operator can face is a machine that refuses to start. If your CAT 955L won’t run, there are a variety of possible causes that need to be investigated.
In this article, we will explore the potential reasons behind a CAT 955L that won’t start, common symptoms, and step-by-step troubleshooting tips to get your loader back to work. Along the way, we’ll also discuss useful maintenance practices to avoid these problems in the future.
1. Potential Causes of a CAT 955L That Won’t Run
When a CAT 955L refuses to start, it can be due to a variety of reasons, both mechanical and electrical. Understanding the root cause of the problem is essential to effective troubleshooting and repair. Below are the most common issues that may cause a CAT 955L to fail to start:
1.1 Fuel System Issues
The fuel system is one of the first places to check when troubleshooting a machine that won't start. Common fuel-related problems can prevent the engine from firing up. These issues include:

• Clogged Fuel Filters: Over time, fuel filters can become clogged with debris, restricting fuel flow to the engine.
  
• Air in the Fuel Lines: Air in the fuel lines can cause poor fuel delivery and engine stalling.
  
• Fuel Pump Failure: A malfunctioning fuel pump can fail to provide the necessary fuel pressure for the engine.
  
• Empty Fuel Tank: Though it seems simple, sometimes the fuel tank may be empty or nearly empty, which could easily be overlooked.
  

1.2 Electrical System Failures
The electrical system of the CAT 955L plays a critical role in starting the engine, powering the fuel system, and operating the ignition system. Faults within the electrical system can easily prevent the engine from starting. These include:

• Battery Issues: A weak or dead battery is one of the most common causes of a machine failing to start.
  
• Faulty Ignition Switch: The ignition switch can wear out over time, preventing the system from properly engaging the starting circuit.
  
• Wiring Issues: Loose or corroded wires can interrupt the power supply to key components, such as the starter motor, fuel pump, or ignition system.
  

1.3 Starter Motor Problems
The starter motor is responsible for cranking the engine when the ignition is turned on. If the starter motor fails, the engine won't turn over, and the machine won't start. Common problems with the starter motor include:

• Sticking or Seized Starter: If the starter motor gets stuck or is seized, it won’t engage and rotate the engine.
  
• Faulty Solenoid: A malfunctioning solenoid can prevent the starter motor from receiving the proper electrical signal.
  
• Worn Brushes or Commutator: Over time, the brushes and commutator in the starter motor can wear out, reducing the motor’s effectiveness.
  

1.4 Hydraulic System Issues
In some cases, the loader may refuse to start due to issues within the hydraulic system. While this is less common than fuel or electrical problems, it's still worth investigating.

• Low Hydraulic Fluid Levels: Insufficient hydraulic fluid can cause the machine’s engine to fail to start. Low fluid levels can occur if there are leaks in the system or if the fluid hasn’t been topped off for a while.
  
• Hydraulic Pump Failure: A malfunctioning hydraulic pump can affect the power and performance of the loader, potentially preventing it from starting.
  

1.5 Engine Compression Problems
If the engine is not producing sufficient compression, it may be difficult, if not impossible, to start. Loss of compression can occur due to:

• Worn Piston Rings: Worn piston rings can cause compression loss, preventing the engine from starting.
  
• Blown Head Gasket: A blown head gasket can also cause compression issues, as it allows coolant or oil to mix with the air-fuel mixture, affecting engine performance.
  
• Valves Not Sealing Properly: If the valves are not sealing properly, the engine won’t generate enough compression to start.
  

2. Step-by-Step Troubleshooting Process
To troubleshoot the issue of a CAT 955L that won’t run, follow this step-by-step guide to systematically identify and fix the problem.
2.1 Check the Fuel System

• Step 1: Verify that there is fuel in the tank. Sometimes the issue is as simple as running out of fuel.
  
• Step 2: Inspect the fuel filter for any signs of clogging or dirt buildup. If the filter looks dirty, replace it.
  
• Step 3: Check for air in the fuel lines. Bleed the lines to ensure that fuel is flowing freely to the engine.
  
• Step 4: Test the fuel pump to ensure it is operating correctly. If the pump is malfunctioning, it will need to be replaced.
  

2.2 Inspect the Electrical System

• Step 1: Check the battery voltage with a multimeter. If the voltage is too low, recharge or replace the battery.
  
• Step 2: Test the ignition switch for continuity. If the switch is faulty, replace it.
  
• Step 3: Inspect the wiring for any loose, corroded, or damaged connections. Repair or replace wires as necessary.
  
• Step 4: Check the starter motor and solenoid for faults. If the motor is not functioning correctly, it may need to be rebuilt or replaced.
  

2.3 Examine the Starter Motor

• Step 1: Attempt to turn the starter motor manually (if accessible). If the motor is seized, it will need to be serviced or replaced.
  
• Step 2: Test the starter solenoid by bypassing it with a jumper wire. If the starter engages, the solenoid may need to be replaced.
  

2.4 Check the Hydraulic System

• Step 1: Verify the hydraulic fluid levels. If the fluid is low, top it up with the appropriate type of hydraulic fluid.
  
• Step 2: Inspect the hydraulic pump for any signs of wear or damage. A faulty pump will need to be replaced to restore function.
  

2.5 Assess Engine Compression

• Step 1: Use a compression gauge to test the engine’s compression. If the readings are low, inspect the piston rings, head gasket, and valves for wear.
  
• Step 2: Repair or replace any worn or damaged components to restore engine compression.
  

3. Preventative Maintenance Tips
Regular maintenance is key to preventing issues with starting the CAT 955L. Follow these maintenance tips to ensure the machine runs smoothly:

• Check the fuel system regularly for leaks, filter clogs, and proper fuel flow.
  
• Inspect the battery and electrical components for corrosion or loose connections.
  
• Change hydraulic fluid at recommended intervals to keep the system running smoothly.
  
• Service the starter motor and check the solenoid for wear and tear.
  
• Test engine compression periodically to detect any potential issues early.
  

4. Conclusion
A CAT 955L that won’t run can be caused by a variety of issues, ranging from fuel system problems to electrical failures. By following the troubleshooting steps outlined above, operators can identify and address these issues systematically. Regular maintenance of the fuel system, electrical components, hydraulic system, and engine will help prevent future starting problems and extend the lifespan of the equipment.
Always remember to consult the operator’s manual and seek professional advice when necessary. Keeping your CAT 955L in optimal condition through preventative maintenance is the best way to avoid costly repairs and minimize downtime on the job.