LG Heat Pump Error Code E291

E291 indicates a high pressure sensor circuit error on an LG heat pump. The control board has detected that the sensor signal voltage is either below 0.4V (SHORT error) or above 4.2V (OPEN error). This fault is detected when the compressor is getting ready to operate, and the unit will not start until the issue is corrected. The root cause is typically a wiring problem or a failed sensor.

The unit is designed to prevent compressor operation when E291 is active, so it will not run normally in this state. You should not attempt to override or bypass this protection. Continuing to attempt forced operation without a functioning pressure sensor could result in compressor damage or an unsafe refrigerant pressure condition. Address the fault before returning the unit to service.

Repair costs vary depending on the cause. If the fix is simply reseating a loose connector, a service call fee may be the primary expense, typically in the range of $75 to $150. Replacing a failed high pressure sensor generally adds $100 to $300 in parts and labor depending on the model and technician rates. Harness repairs or control board replacement would increase costs further, potentially reaching $300 to $600 or more.

A knowledgeable DIYer can begin by checking the high pressure sensor connector and wiring harness for obvious issues like a loose plug, damaged insulation, or corroded terminals. However, if the wiring appears intact and the sensor itself needs testing or replacement, a qualified HVAC technician should be involved since the sensor is located in the refrigerant circuit and proper diagnosis requires electrical measurement tools.

A power reset may temporarily clear the error from the display, but the fault will return as soon as the compressor prepares to operate again if the underlying problem has not been fixed. The control board checks the sensor voltage each time the compressor is ready to start, so the error will reappear until the wiring, connector, or sensor is repaired or replaced.