The electric pressure cooker displays E4 after plugging in, which is caused by a defective pressure switch or a malfunction of the pressure switch. Reason: The pressure switch gets electric shock and is oxidized due to moisture or the pressure is lower than 0.04MP. In this case, you can treat the oxidation point of the pressure switch of the electric pressure cooker and check the solder joints in the power board and control pole to see if there are any problems and repair them.