E4 appears on the display and the cooker refuses to start pressure or high-heat programs.

Safety first: Disconnect power and ensure the cooker is cool. Do not disassemble the lid while it is under pressure.

• Check lid cable: Open the lid and inspect the hinge area where the lid wiring passes into the body. Look for cracked insulation or broken conductors in the flex cable.
• Access lid sensor: Remove the decorative lid cover (usually held by screws from the inner side). Locate the small NTC sensor near the steam outlet or under the inner lid plate.
• Test sensor: Disconnect the sensor from its plug and measure resistance at room temperature. Compare to the bottom sensor value; it should be in a similar kΩ range. Infinite or near-zero resistance indicates a fault.
• Reseat connectors: Unplug and replug the lid sensor connector at both the lid side and the main board side to clear oxidation.
• Replace faulty lid sensor or cable: If the sensor or flex cable is damaged, replace with a Polaris-compatible lid temperature sensor assembly or lid harness for your model.
• Board replacement: If the sensor and wiring test good but E4 persists, the main control board may be defective and require replacement.