Why does my autopilot keep turning off, and what should I check to find the cause?
My autopilot sometimes drops out when the boat is working hard, but occasionally it happens in calm water too. How can I tell whether the problem is the power supply, steering drive or navigation instruments, and what should I check first?
Answer
Your autopilot usually drops out because its supply voltage falls under load, the steering drive overloads, or essential heading or network data disappears. First establish whether it loses power or returns to standby, because each symptom calls for different checks.
1. Identify what switches off
When it next happens, note the alarm wording, operating mode and display behaviour before pressing any buttons. Keep someone at the helm ready to steer manually throughout testing.
- Screen goes blank or shows its start-up screen: suspect an interrupted supply, low voltage or an internal fault.
- Screen stays on but changes to standby: investigate the alarm, drive load, missing sensor data or an external disengage command.
- Chartplotter loses pilot controls but the pilot still steers: investigate communications and chartplotter settings.
- Only the wireless remote stops responding: check its batteries, sleep mode and wireless connection first.
Record whether it happens during a large course change, in waves, after prolonged operation or when another electrical load starts. A dropout when a fridge or bow thruster starts strongly suggests a supply problem. One after repeated heavy steering suggests overload or heating.
2. Measure voltage under load
A healthy-looking battery monitor does not prove that enough voltage reaches the autopilot. A corroded fuse holder or loose negative connection can pass enough current for the display but fail when the motor starts.
Isolate the supply before opening connections. Keep hands and meter leads clear of moving steering gear.
- Inspect the battery connections, isolator, breaker, fuse holder and both positive and negative terminals at the pilot computer or drive supply.
- Look for green corrosion, loose crimps, darkened insulation and signs of heat. Tighten terminals to the equipment maker's specified torque.
- Measure voltage directly across the pilot's supply terminals while commanding a moderate turn in safe conditions. Use the meter's minimum-recording function if available.
- Compare this with battery-terminal voltage under the same load. If the battery voltage stays steady but voltage at the pilot falls, investigate the wiring and connections.
On a nominal 12 V installation, a drop of around 0.5 V between the battery and pilot under working load deserves investigation. The low-voltage shutdown threshold depends on the model. For a precise diagnosis, measure voltage drop along the positive and negative paths separately while current flows.
Check cable size against the manufacturer's current and cable-length table, using the complete outgoing-and-return circuit length. Never fit a larger fuse to stop nuisance trips. The fuse must protect the cable and match the installation specification.