Battery
Common no-start cause. Match size, terminal layout, and cold-cranking requirements.
Generac Auto Transfer Switch Error Codes
Generac automatic transfer switches (RTS, RTSC, RXSW, and HTS series) manage the automatic switching between utility power and generator power. Faults in the transfer switch can prevent power transfer even when the generator is running correctly.
Generac ATS Controller Error Codes
| Code | Fault Description | Common Cause | Action |
|---|---|---|---|
| ATS E01 | Transfer failure | Contactor solenoid not engaging | Test solenoid coil resistance (15-25 ohms), check wiring |
| ATS E02 | Return failure | Switch won’t return to utility | Check utility sensing voltage, T1 fuse, harness |
| ATS E03 | Utility loss sense | Controller lost utility input signal | Test utility voltage at ATS terminals, T1 fuse |
| ATS E04 | Controller communication | Lost signal between ATS and generator | Check 4-wire control harness, connectors |
| ATS E05 | Motor operator fault | Motor operator failed (HTS series) | Test motor winding, capacitor |
| ATS E06 | Thermal overload | Switch operated too frequently | Let cool 15 min, check for unstable utility |
| ATS E07 | Position sensor fault | Switch position not confirmed | Test microswitches, limit switch adjustment |
| ATS E08 | Phase loss | One phase of utility lost | Check utility supply, ATS wiring connections |
| ATS E09 | Frequency fault | Utility frequency out of range | Contact utility provider |
| ATS E10 | Controller battery low | ATS backup battery low | Replace ATS controller battery (CR2032) |
Generac ATS LED Status Indicators
| LED Pattern | Meaning | Action |
|---|---|---|
| Green solid | Normal — utility power active | None |
| Green flashing | Generator running, not yet transferred | Normal during warm-up |
| Yellow solid | Switch in maintenance bypass | Remove bypass |
| Yellow flashing | Switch exercising | Normal |
| Red solid | Fault detected | Read error code from controller |
| Red flashing | Transfer in progress | Wait 10 seconds for completion |
| No LED | No power to controller | Check battery, T1 fuse, utility input |
Most Common Generac ATS Faults
Chattering or Rapid Clicking
The most common ATS complaint. The contactor solenoid tries to engage but the power drops mid-throw, causing rapid cycling. This damages the contactor and control board over time. Primary causes in order: (1) low battery voltage at the ATS controller — test with a multimeter at the controller terminals, (2) loose or corroded connections in the control harness, (3) failed ATS control board that can’t sustain the solenoid pull current.
Quick test: measure voltage at the ATS controller with the generator running and transfer command active. Voltage should stay above 11V DC. If it drops below 10V, the battery or charger is failing.
Generator Runs But No Transfer
The generator starts and runs but the house stays dead. First confirm the ATS hasn’t tripped the main breaker. Then check the control harness between the generator and ATS. The 4-wire harness (two signal wires, two power wires) can be damaged by rodents, lawn equipment, or vibration. Test continuity on each wire. If the harness is good, the ATS controller board has likely failed.
Manual Transfer Handle Stuck
If you need to manually transfer and the handle won’t move, the switch mechanism may be bound. Do not force it. Turn off both utility power (at the main breaker) and the generator (at the generator breaker). Wait 30 seconds. The handle should now move freely to the opposite position. If it’s still stuck, the contactor may be welded from a fault condition.
Utility Sensing Failure
The ATS controller monitors utility voltage through the T1 fuse and sensing transformers. If the T1 fuse blows (often from a utility surge or brownout), the controller thinks utility power is lost and keeps the generator running. Replace the T1 fuse (3A, 250V, ~$2 at any hardware store). If the new fuse blows immediately, there’s a short in the sensing circuit.
Parts Reference
| Part | Part Number | Cost | Where to Buy |
|---|---|---|---|
| ATS control board (RTS) | Generac 0G3431 | $150-$250 | Generac Parts |
| ATS control board (RXSW) | Generac 0H4228 | $200-$350 | Generac dealer |
| T1 fuse (3A 250V) | Generic 3AG | $2-$5 | Any hardware store |
| Contactor (RTS 200A) | Generac 0G2719 | $80-$150 | Generac Parts |
| Control harness (4-wire) | Generac 0G3847 | $30-$55 | Generac Parts |
| CR2032 battery | Generic | $3-$5 | Electronics store |
Technician Tips
Generac generator fault codes are displayed as flashing LED patterns on the controller. The red LED indicates a fault condition; green means normal operation. Code 1500 (low oil pressure) is the most common Generac fault — check oil level first, then the oil pressure switch. Generac generators have a built-in exercise cycle (every 7 days) — if the generator fails its exercise test, it logs a fault that may not trigger a warning light. Check the controller’s fault history to find these logged events.
Maintenance: Generac recommends oil changes every 100 hours of operation or annually. Skipping oil changes accelerates wear, sludge buildup, and low-oil shutdowns, so log each service interval and verify the controller maintenance timer after service.
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.