CASE 70XT Electrical Shutdown Issue

[MikePhua]

The CASE 70XT skid steer loader is a compact, powerful machine used for various material handling, landscaping, and construction tasks. A reported problem with the 70XT involves it starting and running for about 20–30 seconds, then shutting down completely—losing all electrical power—before relays reset and the machine restarts. Below is a detailed look into this behavior: what might cause it, relevant technical concepts, diagnostic steps, and possible fixes.

Machine Background and Specs

• Manufacturer: Case Construction / CNH Industrial
  
• Model: 70XT skid steer loader
  
• Engine: CASE 4T-390, four-cylinder, turbocharged diesel, displacement ~239 in³ (~3.9 L).
  
• Power: Gross ~85 hp, net ~79 hp at around 2,200 RPM.
  
• Operational Weight: ~6,900 lb (≈ 3.13 tons) depending on attachments.
  
• Electrical System: Includes fuses, circuit breakers, relays (notably engine shut down relay, fuel solenoid relays, seat/seat bar safety switches), and wiring harnesses.
  

Understanding these helps contextualize potential failure points in the electrical circuit.

What’s Happening: Symptoms & Pattern

• The loader starts normally, runs for 20-30 seconds, then abruptly dies.
  
• Following shutdown, all electrical systems lose power: dashboard, lights, relays, etc.
  
• After waiting around 15 seconds, operators report hearing relays reset, then the machine starts again.
  
• The shutdown seems repeatable, following the same timing/pattern.
  

These behaviors suggest that something in the power / control circuit is interrupting supply—either through a protective component (fuse, breaker), a relay, or a safety interlock—rather than purely mechanical or fuel delivery failure.

Key Terms and Concepts

• Circuit Breaker: A protective device designed to open a circuit automatically under overload or short circuit conditions. If overheating or overcurrent occurs, it “trips” and cuts off power.
  
• Relay: An electrically-operated switch. For example, an engine shut down relay closes or opens the power to certain circuits (fuel solenoids, control power, etc.). If that relay fails or loses power/ground, it can cut power.
  
• Seat Switch / Seat Bar / Seat Bar Switch: Physical safety interlock so loader won’t operate unless the seat bar is down / operator is seated / safety bars engaged. If the switch is faulty, it may mistakenly open the circuit, causing shutdown.
  
• Lock / Interlock Fuse: A fuse specially assigned to safety or control circuits (interlocks). In some reports, the 70XT keeps blowing a “15 amp Lock/Interlock” fuse.
  
• Ground / Earth: The electrical return path. Poor ground connection can cause voltage drop, intermittent power loss, or relay chatter.
  
• Electrical Overload / Short: Drawing too much current due to some component failing (e.g. shorted wiring, failed relay coil) can cause protective devices to trip (breaker or fuse) and cut power.
  

Potential Causes
Based on the symptoms, several likely causes emerge:

1. Weak or failing circuit breaker or a breaker that is tripping under load — The operator’s description (machine running then dying) aligns with a breaker that cannot handle a surge once all systems activate. Once it cools or resets, power returns.
   
2. Fuse blowing (Lock/Interlock fuse) — The 15A fuse named “Lock/Interlock” has been reported blown in similar cases. If that fuse is intermittently blowing, it will cause complete shutdown of interlocked power circuits.
   
3. Faulty relay (particularly engine shut down relay or fuel solenoid relay) — If the relay that keeps fuel supply or ignition enable gets de-energized, engine will stop. A bad relay, or relay coil failing under heat or vibration, may cause the shutdown. The service manual shows that in 70XT, the "engine shut down relay (15)" plays a central role in holding power to the fuel solenoid and enable circuits.
   
4. Seat bar / seat switch or safety interlocks — If an interlock thinks the operator is not in position or safety bar is open, it may cut the circuit. A loose or dirty seat switch or bar switch could open momentarily once machine starts, causing shutdown.
   
5. Wiring or ground fault — Wire insulation damage, loose connectors, or grounds getting intermittent can cause circuits to lose continuity. This can mimic a blown fuse or failing relay but be harder to trace.
   
6. Fuel hold-in or pull-in solenoids not staying energized — Some reports for similar machines indicate that if the fuel solenoid momentary (pull-in) works but the “hold-in” coil fails, the engine will run briefly then die once initial impulse ends.
   

Diagnostic Steps
Here are a systematic method to find the root cause:

• Check the 15A Lock/Interlock fuse: Inspect visually for blown fuse; test fuse under load. Replace if faulty, and see if it still blows.
  
• Monitor circuit breaker(s): Identify which breaker(s) sit under or near the relay block beneath or behind dash. Look for hot spots or evidence of overheating. Possibly swap with known good identical breaker to see if behavior changes.
  
• Test relays:
  • Engine Shut Down Relay (Relay #15 in many 70XT electrical manuals).
  • Fuel Solenoid Relays / Pull-In / Hold View.
  • Check relay coil voltage when running just before shutdown, to see if coil loses power.
  
• Inspect safety switches:
  • Seat bar switch — ensure it is making solid contact when operator is seated and bar is down.
  • Seat switch — sometimes also a seat sensor.
  • Any door/cab safety interlocks (if configured).
  
• Check wiring and grounds:
  • Ground between battery negative, engine block, and chassis. Ensure tight, clean.
  • Inspect wiring harnesses near steering column, under seat, under dash for chafed insulation or vibration damage.
  • Use continuity / resistance checks on wires feeding relay coils and fuse feed lines.
  
• Measure voltage during shutdown:
  • Use voltmeter to monitor voltage on key terminals (battery positive, fuse feed, relay coil supply, ground) just before and during shutdown. See which drops.
  
• Test fuel solenoid behavior:
  • If possible, manually hold the solenoid or bypass its hold-in coil temporarily to see if machine stays running. If yes, solenoid hold coil is likely bad.
  
• Check operating temperature:
  • Sometimes relays or components fail when hot. Run machine a bit, feel components or measure temperature around relays / relay block.
  

Possible Solutions
Depending on diagnostics, fixes might include:

• Replace the 15A Lock/Interlock fuse with correct type; ensure fuse holder is secure and clean.
  
• Replace worn or faulty circuit breaker(s) that are tripping.
  
• Replace faulty relays (especially engine shut down relay, fuel pull-in / hold relays).
  
• Repair or replace seat bar switch / seat switch / any safety interlock that opens unexpectedly.
  
• Repair wiring: replace damaged harness connectors, repair or re-terminate loose connections, clean and tighten grounds.
  
• If fuel solenoid hold coil is failing, replace solenoid or repair coil (if possible)—make sure proper voltage is feeding and coil is functioning.
  
• Inspect relay block for water intrusion or corrosion; seal or protect that area to prevent future failures.
  

Preventative Maintenance Suggestions
To avoid similar electrical shutdown problems in the future, operators should:

• Inspect fuses, relays, circuit breakers regularly (e.g. during routine maintenance every 250 hours).
  
• Clean all connectors and grounds; protect from moisture / dirt ingress.
  
• Ensure safety switches are functioning; keep them clean and properly adjusted.
  
• Monitor electrical currents or signs of overheating in relays or fuse panels.
  
• Keep service manuals or wiring diagrams handy to identify component numbers, wire colors, terminal IDs.
  

Conclusion
The CASE 70XT electrical shutdown—machine starts, runs for some seconds then dies with total electrical loss—is most likely caused by an issue in the safety interlock / relays / fuse/breaker circuit. Key suspects include the Lock/Interlock fuse, the engine shut down relay, fuel solenoid solenoids (especially hold-in coil), seat or seat bar safety switches, and wiring/grounds. A methodical diagnostic approach, combined with replacement of failing components and preventive maintenance, generally resolves the issue and prevents recurrence.