Battery
Common no-start cause. Match size, terminal layout, and cold-cranking requirements.
Kohler Error Code 13 — Voltage Regulator Fault Fix
What it means: The Decision-Maker controller detected that the generator is running but the AVR (automatic voltage regulator) is not producing correct output voltage. This is a common fault on Kohler generators after extended idle periods or following a load-side short circuit.
Common Causes
| Cause | Frequency | Fix Difficulty |
|---|---|---|
| Blown AVR fuse | Medium | Easy |
| AVR failed open (no output) | Medium | Moderate |
| Rotor flash lost (residual magnetism gone) | Medium | Moderate |
| Shorted rotating diodes | Low | Moderate |
| Open exciter winding | Low | Hard |
Step-by-Step Fix
1. Check the AVR Fuse
Kohler AVR modules have a built-in fuse or a cartridge fuse in line with the field output. Test continuity with a multimeter. A blown fuse indicates a downstream short — don’t just replace the fuse without tracing the cause. Test rotor resistance first.
2. Test Rotor + Exciter Winding Resistance
With the generator off and battery disconnected, measure resistance across the rotor brushes. A healthy Kohler rotor reads 5–25 ohms depending on model. Also test the exciter stator winding (the stationary field winding) — it should read 10–50 ohms. An open reading (OL) on either means replacement is needed.
3. Test AVR Output
Reconnect the AVR, start the generator, and measure DC voltage across the brush terminals. A working AVR outputs 5–15 VDC at no load. If you see 0 VDC with good AC input to the AVR and a healthy rotor, the AVR has failed. Kohler AVR part GM71908 ($120-$200) fits most residential models.
4. Flash the Rotor (if residual magnetism is lost)
If the generator has been sitting unused for months, the rotor may have lost residual magnetism. With the generator stopped, apply 12V DC from a battery directly to the brush leads for 2-3 seconds (positive to positive, negative to negative). Restart the generator — it should now build voltage. If it does, the AVR is fine and the issue was only loss of residual magnetism. This is a zero-cost fix.
5. Check Rotating Diodes
On Kohler brushless generators, the exciter armature output goes through rotating diodes mounted on the rotor shaft. A shorted diode will prevent voltage buildup. Test each diode with a multimeter diode test function — a good diode reads ~0.5V in one direction and OL in reverse. Replace the diode pack if any are shorted.
Parts Reference
| Part | Part Number | Cost | Where to Buy |
|---|---|---|---|
| AVR (residential) | Kohler GM71908 | $120-$200 | Kohler Parts |
| AVR (industrial) | Kohler GM72405 | $250-$600 | Kohler dealer |
| Diode pack assembly | Kohler A-238290 | $35-$65 | Kohler Parts |
| AVR fuse (5A) | — | $2-$5 | Electronics supply |
Need Replacement Parts?
Before ordering, match the generator part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.