Diagnosing No-Spark Crank Issues in the Komatsu FG25T-14 Forklift

[MikePhua]

The FG25T-14 and Komatsu’s Forklift Lineage
The Komatsu FG25T-14 is part of Komatsu’s long-standing FG series of internal combustion forklifts, designed for mid-capacity material handling in industrial and warehouse environments. Komatsu, founded in 1921, has built a reputation for durable construction equipment and reliable powertrains. The FG25T-14 typically features a Nissan or Komatsu-built gasoline or LPG engine, electronic ignition, and a compact chassis optimized for maneuverability and load stability.
By the early 2000s, Komatsu had sold tens of thousands of FG-series forklifts globally, with strong adoption in logistics, manufacturing, and rental fleets. The FG25T-14, with its 5,000 lb lift capacity and hydrostatic steering, remains a workhorse in many facilities—but like all machines, it can suffer from intermittent electrical faults that require methodical diagnosis.
Crank But No Spark Symptoms
A common issue reported in FG25T-14 units is a crank-no-start condition accompanied by a complete absence of spark. The engine turns over normally, fuel delivery appears intact, but ignition fails to initiate combustion. This behavior typically points to a fault in the ignition control system, which may include:

• Ignition coil failure
  
• Crankshaft position sensor malfunction
  
• Faulty ignition control module (ICM)
  
• Wiring harness damage or connector corrosion
  
• ECU lockout or immobilizer interference
  

In some cases, the issue arises suddenly after the machine has been running without problems—suggesting a thermal failure or electrical degradation rather than a gradual mechanical fault.
Using the Pedal Dance for Diagnostic Codes
The FG25T-14 features a diagnostic system that can be accessed via a sequence known as the “pedal dance,” where the operator cycles the accelerator pedal to trigger fault code retrieval. A flashing green light on the dashboard indicates system readiness. After counting a set number of flashes—typically 100—the machine should display a four-digit fault code.
However, if no code appears, it may indicate:

• Improper pedal sequence timing
  
• Fault code memory not triggered
  
• Dashboard LED malfunction
  
• ECU not receiving sensor input
  

To improve accuracy:

• Ensure the key is in the ON position without cranking
  
• Depress the pedal fully and release in consistent intervals
  
• Count flashes carefully and wait for the code display
  
• Consult the service manual for model-specific code retrieval instructions
  

If the system fails to produce a code, manual inspection of ignition components becomes necessary.
Ignition System Breakdown and Testing
The ignition system in the FG25T-14 includes several key components:

• Ignition coil: Converts low voltage to high voltage for spark plug firing
  
• Distributor or coil pack: Routes spark to each cylinder
  
• Crankshaft position sensor: Signals engine rotation to the ECU
  
• Ignition control module: Manages timing and spark delivery
  
• Spark plugs and wires: Deliver spark to combustion chamber
  

Testing procedure:

• Use a spark tester to verify output from the coil
  
• Check resistance across coil terminals (typically 0.4–2.0 ohms primary, 6k–15k ohms secondary)
  
• Inspect crank sensor for damage and test voltage signal during cranking
  
• Verify continuity in ignition wiring harness
  
• Replace spark plugs if fouled or worn
  

In one documented case, a forklift in Virginia failed to start after routine shutdown. The technician traced the fault to a failed ignition control module, which had overheated and ceased functioning. Replacing the module restored spark and normal operation.
Wiring Diagram and Electrical Schematic Access
Access to a wiring diagram is essential for tracing faults in the ignition circuit. The FG25T-14’s electrical system includes multiple connectors, relays, and fuses that can interrupt spark delivery. Without a schematic, technicians must rely on visual inspection and continuity testing.
Recommended steps:

• Locate the ignition fuse and verify voltage supply
  
• Inspect all connectors for corrosion, especially near the ECU and coil
  
• Use a multimeter to test voltage at key points during cranking
  
• Check ground straps and battery terminals for secure contact
  

If a wiring diagram is unavailable, contacting Komatsu support or referencing a similar model’s schematic may provide enough guidance to proceed.
A Story from the Shop Floor
In a busy warehouse outside Richmond, a Komatsu FG25T-14 suddenly refused to start after lunch break. The operator reported normal operation before shutdown, but the machine cranked with no spark. After checking the coil and plugs, the technician discovered a loose ground wire near the ECU. Once tightened, the forklift fired immediately. The incident led to a shop-wide inspection of all ground connections, preventing future downtime.
Conclusion
A crank-no-start condition with no spark in the Komatsu FG25T-14 is often electrical in nature, involving ignition control components, sensor input, or wiring faults. While diagnostic codes can aid troubleshooting, manual testing remains essential when electronic feedback is absent. With a systematic approach—starting from the coil and working through the harness—technicians can isolate the fault and restore operation. In high-demand environments, even a single wire can halt productivity, making vigilance and documentation key to long-term reliability.