Daikin Error Code E4: Low Pressure Trip (Meaning, Causes, Fixes)
What the code means
Daikin's SkyAir inverter service manual SiUS25-501 titles E4 "Outdoor Unit: Actuation of Low Pressure Switch," though on these units it's detected by the low pressure sensor: the error is set when suction pressure drops below a specific value. Before that, the unit tries to protect itself by limiting compressor speed as low pressure falls, then going into low pressure standby when the sensor reads under about 10 psi. Daikin says that when low pressure standby happens 3 times within 60 minutes, in cooling or in heating, the unit outputs E4. The outdoor board's own monitor mode lists E4 as "Abnormal suction pressure." Daikin's Simple Self-Diagnosis code list uses the same meaning, "Actuation of low pressure switch (LPS)," across its split, SkyAir and VRV equipment. E4 isn't in the error table for Daikin's Entra wall-mount mini splits, so check your model's manual if you see E4 on a wall-mount unit.
Likely causes
- An abnormal drop in low pressure from a refrigerant shortage ("out of gas"), usually a leak somewhere in the system. This is the first cause in Daikin's flowchart.
- Shutoff (stop) valves left closed at the outdoor unit after installation, which Daikin lists both as a supposed cause and as an installation mistake.
- Refrigerant system clogging, or an electronic expansion valve stuck fully closed.
- Wiring and piping connected to the wrong unit (wrong connection) on systems with more than one line set.
- On a new install, the remote controller's operating mode was changed before the check run; Daikin says to set every indoor unit to cooling for the check run.
- A defective low pressure sensor, a defective connector contact, or a defective outdoor unit PC board.
Safe DIY checks
Turn off the power at the breaker or outdoor disconnect before opening any panel; the outdoor inverter board can hold a dangerous charge after power is removed. Leak repair, refrigerant recovery and recharging must be done by a certified technician (in the US, EPA Section 608 certification is required). Don't keep resetting a unit that trips on low pressure, since running short of refrigerant can damage the compressor.
- Turn the system off and check the indoor unit's air filters. Clean them if they're dusty, and make sure supply and return grilles aren't blocked, since poor indoor airflow lowers suction pressure.
- Look for obvious problems at the outdoor unit and the line set: crushed or kinked copper lines, oily spots at fittings (a sign of a refrigerant leak), or ice on the lines.
- Turn the power off at the breaker or disconnect, wait a few minutes, then restore power and restart once.
- If E4 shows up right after a new installation, call the installer: closed shutoff valves and a check run done in the wrong mode are installation fixes Daikin calls out by name.
- If E4 comes back after a reset, stop running the system and call a licensed HVAC technician. Low pressure usually means a refrigerant problem that needs a certified tech.
🛠 When to call a pro
- Following Daikin's SiUS25-501 flowchart: confirming the stop valves are fully open on both the gas and liquid side, and opening them if not.
- Confirming whether low pressure really dropped, and if so checking for low charge or a leak, refrigerant system clogging, wrong wiring or piping connections, and an electronic expansion valve stuck fully closed.
- If low pressure is actually normal, measuring the sensor voltage (VL) at X45A pins 2 and 3 on the outdoor PC board (A1P) and comparing it to Daikin's pressure sensor pressure/voltage table. If the voltage matches the pressure, replacing the low pressure sensor; if not, replacing the outdoor PC board.
- On a new install, confirming the additional refrigerant charge was finished and recalculating the required charge from the piping length, then running the check operation with all indoor units set to cooling.
- Checking connector contact at the low pressure sensor, per Daikin's self-diagnosis code list.
Parts that commonly fix it
Always match the part number to your exact model.
Refrigerant leak detector
For techs and DIYers confirming a leak, the most common reason suction pressure drops; the repair and recharge still need a certified tech.
Search eBay →Low pressure sensor
Only if the sensor voltage doesn't match the actual pressure; order by your outdoor unit model number.
Search eBay →Outdoor control board
Daikin's last step when the sensor checks out and E4 keeps returning; match it to your exact outdoor unit model.
Search eBay →Sources
- Daikin SkyAir Inverter service manual SiUS25-501, 4.15 "E4" Outdoor Unit: Actuation of Low Pressure Switch (pp. 111-112), 4.2 low pressure protection control, outdoor PCB monitor mode and installation nonconformity table, Daikin Comfort
- Daikin Industries, Simple Self-Diagnosis by Malfunction Code (E4 actuation of low pressure switch: abnormal drop in low pressure, defective low pressure sensor, defective outdoor unit PCB, defective connector contact)
- Daikin Entra wall mount service manual FTK(X)B/RK(X)B AXVJU, 3.3 inverter error code table (no E4), Daikin Comfort
Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.