Generator Output Low or No Voltage Detected
The ALLMAND-16 (COMMANDER controller) diesel fault code means: Generator Output Low or No Voltage Detected. This is a serious severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- moderate
- Estimated cost
- DIY brush and AVR replacement: $40-$150 in parts. Professional diagnosis and repair: $200-$600 depending on whether the issue is brushes, AVR, field flashing, or winding repair. Rotor rewind or generator head replacement: $800-$2,500 at a generator shop.
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Common Symptoms
- COMMANDER display shows fault code 16 and the unit shuts down or refuses to power lamps
- Metal halide or LED light heads fail to strike even after engine reaches operating RPM
- AC output voltage measured at the output terminals reads well below rated 120/240V
- Engine runs normally but the generator head produces no usable AC power
- COMMANDER fault light illuminates and audible alarm sounds at startup
- Lamp circuit breakers trip immediately or repeatedly when lights are switched on
- AVR status indicator (if equipped) is dark or flashing instead of steady green
Probable Causes (Ranked by Likelihood)
- Failed or worn carbon brushes on the generator exciter, eliminating field current and collapsing output voltage Very Likely
- AVR (Automatic Voltage Regulator) failure, so the field winding receives no regulated excitation signal Very Likely
- Loss of residual magnetism in the rotor (de-magnetized field), often after extended storage or a dead-battery event Likely
- Open or shorted generator field winding, preventing the rotor from building a magnetic field Likely
- Loose, corroded, or broken wiring between the AVR, brush assembly, and generator head terminals Possible
- Engine RPM running low (under-speed) so the generator cannot reach rated frequency and voltage threshold Possible
- Faulty COMMANDER controller voltage sensing circuit incorrectly reading output as low when actual voltage is within spec Less Likely
Step-by-Step Diagnostic Procedure
Start with a safety check. Switch the COMMANDER panel to OFF and verify the engine has stopped completely before opening any access panels or touching generator terminals.
Check engine RPM first. Start the unit, let it warm up, and confirm the COMMANDER display shows RPM at or near the rated speed (typically 1800 RPM for 60 Hz output on North American units). If RPM is low, address the engine speed / governor issue before chasing the voltage fault.
Measure AC output voltage at the generator head output terminals using a multimeter set to AC voltage. Rated output is typically 120V single-phase or 120/240V split-phase depending on model. A reading below 90V or zero volts confirms the fault is real and not a sensor glitch.
Inspect the carbon brushes on the exciter brush holder. Remove the brush access cover on the rear of the generator head. Brushes shorter than 1/4 inch (6 mm) are worn out and must be replaced. Look for cracked, chipped, or stuck brushes that are not making contact with the slip rings.
Check slip ring condition while the brush holder is exposed. The slip rings should be smooth, clean, and copper-colored. Heavy carbon buildup, scoring, or corrosion will prevent good electrical contact. Clean lightly with a lint-free cloth and electrical contact cleaner if needed.
Test the AVR. Locate the AVR module (usually mounted inside the generator head access panel or on a bracket near the brush holder). With the engine running, measure DC voltage across the AVR field output terminals. You should see 10-60V DC depending on load. Zero volts here with the engine running points to a failed AVR. Swap in a known-good AVR if available to confirm.
Flash the field to restore residual magnetism if brushes and AVR check out. With the engine running at rated RPM, briefly connect a 12V DC source (from the tower battery) positive to the field positive terminal and negative to field negative for 2-3 seconds. If the generator output voltage jumps up and stabilizes, residual magnetism was the culprit.
If voltage remains at zero after flashing and you have confirmed good brushes and a working AVR, use a multimeter set to resistance (ohms) with the engine OFF and the unit de-energized. Measure resistance across the rotor field winding via the slip rings. A reading of open (OL) or near zero ohms indicates an open or shorted winding. This requires generator head removal and rewinding or replacement by a qualified shop.
Frequently Asked Questions
What does Allmand code 16 mean on my light tower?
Code 16 means the COMMANDER controller measured AC output voltage from the generator head that is too low to safely run the lights. The engine may be running fine, but the generator portion is not producing usable power. The most common causes are worn carbon brushes, a failed AVR, or a de-magnetized rotor field.
Can I still use the light tower with code 16 active?
No. The lamps will not strike without adequate voltage, and the COMMANDER controller will prevent normal operation to protect the electrical system. You need to resolve the fault before the unit will light up.
How much does it cost to fix Allmand code 16?
If the problem is worn brushes or a lost residual field, you can often fix it yourself for $40-$150 in parts. A failed AVR typically runs $80-$200 for the part plus an hour or two of labor if you hire a technician, putting the total around $200-$400. If the rotor winding itself is damaged, expect $800-$2,500 for generator head repair or replacement at a shop.
My Allmand tower sat in storage all winter and now shows code 16. Is this related?
Very likely yes. Extended storage is a known cause of residual magnetism loss in the rotor. The generator cannot build voltage on its own without that residual field. Try the field-flashing procedure described in the diagnostics steps above using a 12V battery. It takes about 3 seconds and fixes the problem in many cases at zero cost.