Glow Plug Control Issues on the CAT 301.7D CR Excavator

[MikePhua]

The glow plug system on the CAT 301.7D CR excavator is controlled by a timer module, not directly by the ignition switch or an ECM. If the glow plug light stays on for less than a second and the engine struggles to start, the timer may be faulty or the glow plugs themselves may be degraded.
CAT 301.7D CR background and electrical design
The CAT 301.7D CR is a compact radius excavator introduced in the early 2010s, designed for tight-space digging, landscaping, and utility trenching. It features:

• A Yanmar diesel engine with indirect injection
  
• 12V electrical system with automatic glow plug control
  
• Key switch with ON and START positions, sometimes lacking a dedicated GLOW position
  
• Glow plug indicator lamp on the dash
  
• No ECM in most configurations, despite some confusion from service personnel
  

Unlike newer machines with full electronic control, the 301.7D CR uses a standalone glow plug timer module. This module activates the glow plugs and the indicator lamp for a preset duration each time the key is turned to ON.
Glow plug timer behavior and troubleshooting
The timer module typically activates the glow plugs for 2–6 seconds depending on model and ambient temperature. In this case, the light stays on for less than one second, which is insufficient for cold starts.
Key points:

• The timer is triggered by the ignition switch, not by coolant temperature or ECM logic
  
• Some timers (e.g., HCO108) are fixed at 6 seconds
  
• If the timer fails, glow plugs may not receive power even if the lamp flashes briefly
  
• The glow plug lamp only confirms timer activation—not actual plug heating
  

To test the system:

• Use a multimeter to check voltage at each glow plug terminal during key ON
  
• Confirm that all plugs receive 12V for the full timer duration
  
• Measure resistance across each plug to detect internal failure
  
• If voltage is absent or drops early, replace the timer module
  

One technician noted that his Takeuchi machine of similar size started reliably because its glow plugs stayed on longer. The CAT 301.7D CR, by contrast, may suffer from short timer cycles and deep plug placement, making manual testing difficult.
Glow plug access and manual override options
Accessing the glow plugs on the 301.7D CR requires removing the intake manifold, which adds labor time. However, testing can be done without removal using a probe-style multimeter.
For persistent cold-start issues:

• Install a manual push-button circuit to activate glow plugs independently
  
• Use a relay to handle current load and protect the switch
  
• Connect the button to the glow plug power line and indicator lamp
  
• Label the button clearly and train operators on proper use
  

This modification has been used successfully on older machines with unreliable timers. One operator in British Columbia added a manual button and reported consistent cold starts even in sub-zero conditions.
Clarifying ECM confusion and schematic errors
Some service representatives mistakenly claim the glow plug timing is controlled by the ECM. However:

• The 301.7D CR does not include an ECM in most configurations
  
• The glow plug system is fully analog, using a timer module and relay
  
• The operator manual may reflect schematic assumptions that don’t match physical wiring
  

If the key switch lacks a GLOW position, the timer is likely triggered automatically at ON. Replacing the switch with a 4-position unit may allow manual glow control if desired.
Conclusion
Glow plug issues on the CAT 301.7D CR excavator are often caused by short timer cycles or degraded plugs. The system is analog, not ECM-controlled, and can be tested with basic tools. Installing a manual override button offers a reliable solution for cold-start problems, especially in older machines with limited glow duration. Proper testing and schematic review are essential before replacing components.