Cross Brand Fault Guide
E4 Error Code on Air Conditioners
The E4 error code air conditioner owners report covers some of the widest ground of any code. Depending on the maker, it can point to refrigerant pressure, a temperature sensor, a wall controller, or a group of outdoor faults. We have checked what each major brand says and marked clearly where we could not confirm anything.
The Big Picture
What Kinds of Faults Hide Behind E4?
Think of E4 as four different conversations sharing one label. On the brands we could confirm, it falls into these groups. Pick the card that matches your unit, then read the detail further down.
Refrigerant Pressure
Daikin uses E4 for low pressure protection. This is often linked to a refrigerant shortage, so it deserves prompt attention.
Temperature Sensor
Actron uses E4 on several ducted families for the indoor coil sensor, a small thermistor attached to the indoor coil.
Controller Signal
Mitsubishi Electric uses E4 when the indoor board stops receiving signals from the wired remote controller.
Outdoor Group Prefix
On Samsung split displays, E4 is the opening half of a 400 series code, which usually relates to outdoor protection and the inverter.
Panasonic, Fujitsu and LG use different code formats, and we could not confirm E4 for Mitsubishi Heavy Industries. Those are covered in their own section below so nothing gets blurred together.
Daikin
What Does E4 Mean on a Daikin?
Daikin’s malfunction code chart describes E4 as low pressure protection. In other words, pressure on the suction side of the refrigerant circuit has dropped abnormally, and a low pressure switch or sensor has stopped the system. The chart also lists a faulty low pressure sensor, a defective outdoor board and poor connector contact among the possible causes.
Low pressure often goes hand in hand with a refrigerant shortage, which in turn usually means a leak somewhere in the circuit. However, very low airflow across the indoor coil can also drag suction pressure down. So can a restriction in the pipework. That is why a technician tests before assuming a regas is the answer.
We have not published a standalone Daikin E4 guide. The Daikin code hub lists E4 in its quick reference and explains the E group. You may also find the related Daikin E3 high pressure guide useful for comparison.
Why Low Pressure Matters
Refrigerant does more than cool your room. It also carries oil around the circuit and helps cool the compressor. When the charge is low, the compressor can overheat and wear faster. Consequently, running a system that keeps tripping on low pressure risks turning a leak repair into a compressor replacement.
Actron
What Does E4 Mean on an Actron Ducted System?
Actron’s published fault reference lists E4 as an indoor coil inlet sensor fault on its ESP Platinum, ESP Que Platinum, ESP Digital and Advance ducted families. On the Classic ranges, the same code is described as an indoor coil sensor fault. Either way, it concerns one thermistor clipped to the indoor coil.
That sensor helps the system protect the coil from freezing in cooling mode and manage temperatures in heating mode. When its reading goes out of range, the board cannot trust it, so the system stops. The cause might be the sensor itself, its connector, or the wiring back to the board.
Our Actron E4 guide covers this in depth, including where the sensor sits and what technicians test. The Actron code hub explains how meanings shift between controller families, which is especially relevant if you have a WC-02 controlled Serene or UltraSlim system. We could not confirm an E4 meaning for the WC-02 controller.
Mitsubishi
Is Mitsubishi E4 a Controller Problem?
On Mitsubishi Electric systems, yes. Its service manuals group E0 to E5 as remote controller related, and describe E4 as a remote controller signal receiving error. Specifically, the indoor controller board has not received valid data from the wired remote controller for several minutes.
You are most likely to see this on ducted systems, ceiling cassettes and other units with a wall mounted controller. Common triggers include a damaged or loose controller cable, a faulty controller, or a fault on the indoor board. Wall splits that rely only on a handheld infrared remote usually report problems through blinking lamps instead.
What About Mitsubishi Heavy Industries?
We could not confirm a documented E4 meaning for Mitsubishi Heavy Industries. The MHI code list reviewed moves from E3 to E5 without an E4 entry, and MHI notes its codes can vary by model. If an MHI unit shows E4, the model number is essential. Our Mitsubishi code hub explains how to tell the two makers apart.
Samsung
Why Does My Samsung Flash E4 Then Two Numbers?
Samsung wall splits with a two digit display cannot show a four character code in one go. So they show E4, pause, then show the next pair. Together they form a single 400 series code. Samsung generally uses that range for outdoor protection and inverter faults, though it is a pattern rather than a strict rule.
Here are the 400 series codes we have written guides for. If your second pair differs, note it carefully and check the Samsung code hub.
E4 Then 16, Discharge Temperature Protection
The gas leaving the compressor is running hotter than its safe limit. See the Samsung E416 guide.
E4 Then 22, Expansion Valve or Flow Restriction
Refrigerant is not flowing as it should, often because of the expansion valve or a pipe restriction. See the Samsung E422 guide.
E4 Then 58, Outdoor Fan Fault
On most Samsung inverter splits, the outdoor fan is not running the way the board expects. See the Samsung E458 guide.
Older non inverter Samsung units may show a short E4 on its own. Those short codes cover broad groups and vary by model, so we cannot give a single meaning for them.
Not Confirmed
What If You Own a Panasonic, Fujitsu or LG?
None of these three brands uses E4 as part of its standard residential code set, as far as we could confirm. Here is what each actually displays, so you can look up the right thing.
Panasonic
Uses a letter and two digits, mainly H codes for abnormalities and F codes for protection. Retrieve them using the remote check routine. See the Panasonic hub.
Fujitsu
Uses two character codes, often read by counting lamp flashes. Wired controllers may show E, a colon and two digits. See the Fujitsu hub.
LG
Uses CH followed by a number, such as CH05 for communication. See the LG hub for the codes we cover.
Hitachi, Toshiba, Haier and Carrier were not researched for this page. If you have one of those, give us the model number and a photo, and a technician will check the correct manual.
Your Unit
How Do You Confirm Your Brand, Model and Controller?
Since one code means so many things, identification is the most valuable thing you can do before calling. Fortunately, it only takes a few minutes.
- Read the brand on the indoor unit, and check Electric versus Heavy Industries on Mitsubishi units
- Find the compliance label on the side of the indoor unit and photograph the model number
- Photograph the outdoor unit label from a safe position, without removing covers
- Note the wall controller name or model on ducted systems
- Film the display for thirty seconds to capture any split code loop
- Write down whether the system was cooling, heating or starting when E4 appeared
For reference, Mitsubishi Electric wall units commonly start with MSZ and MHI wall units with SRK. Daikin model families include names such as Cora, Alira X and Zena on many wall splits. Actron owners should look for Que, Neo, L Series or WC-02 on the controller.
Safe Checks
What Can You Do Safely Before Booking?
The checks that help depend on the meaning. For a Daikin low pressure code, airflow matters. For a Mitsubishi Electric controller code, a clean reset is the main option. The steps below are safe on every brand.
Note the Code Accurately
Record every character, including any second pair on a Samsung, and the controller type on ducted systems.Check the Filters
Dirty filters reduce airflow across the indoor coil, which can affect pressure and coil temperature readings. Clean or vacuum them if they are dusty.Open the Air Path
On ducted systems, make sure the return air grille is clear and that most supply vents are open.Reset Once
Turn the system off at the controller, switch off the breaker, wait around five minutes, then restore power and restart.Watch for Ice
If you see ice on the indoor coil or pipes, switch the system off and let it thaw. Ice often accompanies low refrigerant or poor airflow.Book if It Returns
A returning E4 needs testing. Do not keep restarting, especially on a Daikin with a low pressure code.
Open more detail
Do not attempt to add refrigerant or open service valves. Refrigerant work in Australia requires an ARCtick licensed technician, and the technicians we send hold the licences their work requires.
Leave all covers in place. Sensors, boards and controller terminals sit behind panels that also carry mains voltage. A technician has the meters and charts needed to test them safely.
Local Factors
Do Australian Conditions Play a Part in E4?
They can contribute, though they are rarely the whole cause. A refrigerant leak can be helped along by corrosion, which is faster in coastal suburbs exposed to salt air. Brazed joints and flare connections on outdoor units near the beach in Sydney, Perth and Adelaide deserve extra attention during servicing.
Sensor faults on ducted systems often relate to roof space conditions. Summer roof temperatures in Adelaide, western Sydney and Perth are severe, and years of heat cycling can weaken wiring and connectors. Humidity in Brisbane adds moisture, which encourages corrosion on terminals.
Controller signal faults can follow storms. A power spike or brownout may upset a controller or indoor board. If E4 appeared straight after a storm, mention it when you book. Our page on air conditioners not working after a power outage covers related issues.
The Repair
What Does a Technician Test for E4?
After confirming the exact model and code table, the technician follows the path that matches your brand’s meaning.
Pressure and Sensor Meanings
- Check airflow, filters and indoor coil condition
- Connect gauges to read operating pressures where relevant
- Search for refrigerant leaks if pressure is low
- Measure sensor resistance against the manufacturer chart
- Inspect connectors and wiring back to the board
- Test the low pressure switch or sensor on Daikin systems
Controller and Outdoor Meanings
- Test the wired controller and its cable on Mitsubishi Electric
- Check controller supply from the indoor board
- Inspect terminals for corrosion or looseness
- Follow Samsung 400 series diagnostics for the specific code
- Check outdoor fan, valve or discharge sensor as required
- Run the system under load to confirm the repair
If a leak is found, it should be repaired before any regas. Topping up without fixing the leak simply delays the next breakdown. Our Sydney split system regas page explains the process in general terms.
No Screen
What If Your Unit Only Blinks a Light?
Many wall splits never show letters at all. A lamp flashes, and the code sits in memory waiting to be read. On those units, you may only learn it is an E4 once a remote check function or a technician’s tool brings it up.
Some Daikin remotes have a check mode that steps through codes until the indoor unit beeps at the stored one. Fujitsu units are usually read by counting flash groups on two lamps. Panasonic remotes have a check routine too, though it returns H or F codes rather than E4. If none of this works for you, simply count the flashes, time the pause and tell us. Avoid experimenting with unfamiliar button combinations, since some open installer menus.
Symptoms Before the Code
Were There Warning Signs Before E4 Appeared?
Often there were, and they can help a technician narrow things down. Faults involving refrigerant and sensors tend to build gradually, while controller faults usually arrive suddenly. Think back over the past few weeks and see whether any of these sound familiar.
Slowly Weaker Cooling
Rooms taking longer to cool, or the system running constantly on hot days, can point to a gradual refrigerant loss on brands where E4 relates to pressure.
Frost or Dripping
Frost on indoor pipes, or water dripping after the frost melts, often accompanies low pressure or poor airflow across the coil.
Erratic Controller
A wall controller that freezes, resets itself or ignores button presses can be an early hint of the Mitsubishi Electric signal fault.
Write down anything you noticed, even if it seems minor. A sound that changed, a smell, or a room that never quite reached temperature can all be useful clues. Our guides on clammy rooms and ice on the outdoor unit cover some of these symptoms in more depth.
Arrange a Visit
When Should You Call for an E4?
Call if the code returns after one reset, if you see ice, if cooling has been weakening for weeks, or if you cannot identify your unit. For a Daikin low pressure code, sooner is better, because continued running can strain the compressor.
We book licensed technicians across the five mainland capitals. Choose your city or call us directly.
For more on how we work nationally, visit our air conditioning service Australia page. The full error code library and the troubleshooting guide are also good next steps.
Questions
Frequently Asked Questions
Does E4 always mean I need a regas?
No. Only the Daikin meaning relates to low pressure, and even then a technician must find the cause first. Other brands use E4 for sensors, controllers or outdoor faults.
Why is there ice on my unit with E4?
Ice often points to low refrigerant or poor airflow across the indoor coil. Switch off, let it thaw and book a technician.
My Samsung shows E4 and 22. Is that two faults?
No. It is one code, E422, shown in two halves because the display is small. It relates to refrigerant flow or the expansion valve.
Is Actron E4 serious?
It is a sensor fault, which is usually less serious than a pressure or compressor fault. Still, the system will not run normally until it is fixed.
What does E4 mean on MHI?
We could not confirm a documented E4 for Mitsubishi Heavy Industries. Note the model number and a technician will check the correct manual.
Can I keep using the system on low settings?
It is better not to. Most systems stop on E4 anyway, and forcing restarts can damage the compressor or other parts.
Why does Panasonic not show E4?
Panasonic uses H and F codes for its standard residential range. If you see something unusual, photograph it and let a technician interpret it.
Seeing E4 and Not Sure What Comes Next?
Tell us your brand, model and full code, and we will arrange a licensed technician in your area.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles