U.S. Motors digital pool pump shows E03 and will not run; sometimes starts then immediately shuts down.

Safety first: De-energize the pump circuit at the breaker and verify all three phases are dead before opening the motor junction box.

• Check breaker and contactor: Inspect the three-pole breaker and any contactor feeding the U.S. Motors pump. Reset the breaker and look for a tripped or burned pole.
• Inspect wiring at the motor: Remove the motor terminal cover. Check that all three phase conductors are securely landed on the L1, L2, L3 terminals. Tighten any loose screws and look for signs of overheating.
• Measure phase-to-phase voltage: With power restored, measure L1-L2, L2-L3, and L1-L3 at the motor terminals. All three readings should be similar (within 2–3%). A missing or low leg indicates a supply issue.
• Correct supply issues: Replace any failed breaker or contactor. Repair or replace damaged conductors.
• Controller reset: After restoring proper three-phase power, power cycle the pump and clear E03. If the error persists with balanced voltage, the phase detection circuit on the drive module may be faulty.