Temperature sensor
Common error-code part. Confirm resistance and connector style.
Generac Error Code 1100 — RPM Sensor Fault Fix
What it means: The Evolution controller received no valid RPM signal from the magnetic pickup sensor. This differs from error 1900 — 1100 means the sensor was dead at startup (no signal at all), while 1900 means the signal was lost during operation.
Error 1100 appears immediately when you try to start the generator. The controller cranks the engine but never sees a valid speed signal, so it shuts down with the sensor fault code.
Common Causes
| Cause | Frequency | Fix |
|---|---|---|
| Mag pickup disconnected from controller | High | Reconnect and verify latching |
| Mag pickup failed (open winding) | Medium | Replace sensor (0G5885) |
| Mag pickup gap too wide | Medium | Adjust to 0.040-0.060” from flywheel |
| Controller connector corrosion | Medium | Clean and reseat connector |
| Mag pickup wiring chafed/shorted | Medium | Repair or replace harness section |
| Evolution controller failed | Low | Replace controller (0G1440) |
Step-by-Step Fix
1. Check the Controller Connector
Before touching the sensor, check the connector at the Evolution controller. Unplug the connector, inspect for bent or corroded pins, and reseat firmly. This is a zero-effort check that resolves a surprising number of 1100 faults — heat cycling in the controller cabinet loosens connector tension over years of operation.
2. Test Mag Pickup Resistance
Disconnect the mag pickup at the sensor (two-wire connector near the flywheel cover). Set your multimeter to ohms (2000 scale). Measure across the two terminals. A good pickup reads 200-600 ohms. An open circuit (OL) means the sensor has failed. A short (near 0 ohms) also means failure.
Generac factory replacement: 0G5885 (~$35). Aftermarket compatible sensors are available for ~$20 but have shorter service life in my experience — the Genuine Generac sensor holds up better to the engine heat.
3. Adjust Sensor Gap
If resistance is good, check the air gap. The sensor should be set 0.040-0.060 inches from the flywheel ring gear teeth. Back the lock nut off, turn the sensor clockwise until it contacts the flywheel, then back it out 3/4 turn. Lock the nut. This is the correct gap for almost all Generac engines.
4. Test AC Voltage at Crank
Reconnect the sensor. Set your multimeter to AC volts (200V AC scale). Back-probe the sensor wires at the controller connector while cranking. You should see at least 1-5 VAC at cranking speed. Below 1 VAC means the gap is too wide or the sensor is failing internally.
5. Check for Intermittent Wiring
If resistance and gap are correct but the code persists, the wiring between the sensor and controller may have an intermittent break. Flex the harness while measuring continuity. Pay special attention to where the harness passes metal brackets and the cooling fan shroud — these are common chafe points.
Parts Reference
| Part | Part Number | Cost |
|---|---|---|
| Magnetic pickup sensor | Generac 0G5885 | $30-$40 |
| Magnetic pickup (alt) | Generac 0J8499 | $20-$30 |
| 8-pin controller harness | Generac 0G3978 | $35-$55 |
| Evolution controller | Generac 0G1440 | $300-$500 |
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.