Auxiliary Power Units (APUs) are critical for comfortable rest periods and engine preservation—but sometimes problems arise. The good news? Many common issues can be fixed quickly with basic checks. Here’s a DIY troubleshooting guide, and tips on when to reach out to APU Center’s professionals.

1. APU Won’t Start
Common Causes: Low battery voltage, fuel delivery blockage, or a blown fuse.
Quick Fixes:

Check battery voltage (should be ≥12.4V).

Inspect and replace blown fuses.

Check fuel supply: ensure the tank has clean, fresh fuel and no sediment blocking the line.
When to Call a Pro: If battery and fuses are fine but it still won’t start, internal fuel pump or control module diagnostics may be needed.

2. Rough Idle or Shutting Off
Common Causes: Dirty fuel filters, clogged air intake, or incorrect idle RPM settings.
Quick Fixes:

Replace fuel and air filters.

Clean intake vents.

Adjust idle settings—refer to your APU manual.
When to Call: Extreme fluctuation in RPM or frequent stalling—let a certified tech check sensors and governor system.

3. No Heat or Cooling
Common Causes: Low coolant level, failed thermostat, or fan malfunction (on cooling models).
Quick Fixes:

Top off coolant to recommended levels.

Inspect for leaks, damage, or frayed hoses.

Ensure thermostat is opening/closing properly.

Check fan operation—blown fuse or motor failure could be culprit.
When to Call: If coolant leaks persist or thermostat/fan replacement is required.

4. Warning Lights or Error Codes
Common Causes: Electrical issues—low battery or open circuits, or sensor malfunctions.
Quick Fixes:

Read codes (many modern APUs display simple error codes).

Inspect wiring harness and connectors for corrosion or looseness.

Reset system by restarting the APU.
When to Call: Persistent codes, recurring faults, or no-code but visible system underperformance—pro-grade diagnostics needed.

5. Excessive Fuel Consumption
Common Causes: Aging fuel lines, injector wear, or poor combustion.
Quick Fixes:

Check for leaking fuel lines.

Ensure injectors are clean or replace.

Service combustion chamber—clean carbon buildup.
When to Call: If fuel draw remains high despite checks, an APU Center technician can perform in-depth calibration and performance tuning.

Additional Pro Tips
Schedule routine inspections: Early fault detection reduces downtime.

Pre-trip self-check: Take 5 minutes before high-idle periods to monitor gauges.

Use OEM parts: Aftermarket gear may void warranties or reduce efficiency.

When DIY Isn’t Enough
APU Center’s certified technicians carry full diagnostic tools and replacement parts. They offer mobile service at truck stops and fleet yards across North America—so you don’t need to haul your rig to a shop. Complex electrical faults, fuel pump rebuilds, or logic board repairs are best left to pros.

Final Thoughts
Basic checks can resolve most APU hiccups. But for persistent or safety-critical issues, professional service prevents unexpected breakdowns and costly repairs. Prevent minor issues today to avoid major repairs tomorrow.

Experiencing ongoing APU trouble? Schedule a deluxe inspection with APU Center now: call (417) 736-3000 or visit Contact Us.