Champion Champion 100177 8.5 kW 439cc Home Standby Generator with 50A ATS FAULT-ATS Error Fix: ATS Fault — Automatic Transfer Switch Malfunction

Error code FAULT-ATS on the Champion Champion 100177 8.5 kW 439cc Home Standby Generator with 50A ATS means: ATS Fault — Automatic Transfer Switch Malfunction. The standby generator controller displays an ATS (Automatic Transfer Switch) fault, indicating the transfer switch did not operate correctly. The ATS is the device that automatically switches the home electrical panel between utility power and generator power. When utility power fails, the ATS should disconnect from the utility and connect to the generator within seconds. When utility power is restored, it transfers back after a time delay. Causes: (1) Mechanical failure — the transfer switch contactors are stuck or worn. Listen for the ATS clicking when it should transfer. If no click, the solenoid coil or contactor mechanism may have failed. (2) Control wiring issue — damaged or loose wires between the ATS controller and the generator. Check all connections at both ends. (3) Utility power issue — the ATS may detect an abnormal utility condition (low voltage, frequency deviation, single-phasing on 240V) and refuse to transfer back to utility. Check utility voltage at the ATS input. (4) ATS controller board failure — the electronic controller inside the ATS has failed. This requires replacement by a qualified electrician. (5) Corrosion on ATS contacts — over time, the contactor surfaces oxidize, causing poor connections or failure to make contact. Regular exercise cycling (weekly) helps keep contacts clean. IMPORTANT: Never bypass or manually override the ATS without proper training — risk of backfeed to utility lines, which is lethal to utility workers.

The most successful fix is "Replace ATS Contactor Assembly" (hard difficulty, ~90 minutes). Estimated DIY cost: $5-$15. HomeMD has 2 community-ranked fixes for this error.

This error is rated critical severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Replace ATS Contactor Assembly") is rated hard difficulty and takes about 90 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Wire labels, Digital camera.

DIY cost: $5-$15. Professional repair typically costs $250-$400. Many homeowners save money by trying the top-ranked community fix first.

The Champion Champion 100177 8.5 kW 439cc Home Standby Generator with 50A ATS has 8 other known error codes, including: FAULT-HIGH-TEMP (High Temperature Fault — Engine Overheating), FAULT-LOW-BATTERY (Low Battery Fault — Controller/Starting Battery Voltage Low), FAULT-OVERCRANK (Overcrank Fault — Engine Failed to Start Within Crank Time), FAULT-OVERSPEED (Overspeed Fault — Engine RPM Exceeded Safe Maximum), FAULT-UNDERSPEED (Underspeed Fault — Engine RPM Below Minimum Operating Speed), and 3 more.

Error code FAULT-ATS also appears on 2 other Champion models: Champion 100179 12.5 kW Home Standby Generator with 200A SE-Rated ATS, Champion 100837 14 kW aXis Home Standby Generator with 200A SE-Rated ATS. The fix may vary by model, so check each model's specific page for tailored repair steps.