Mitsubishi Mini-Split E6 Error: Communication Fault
Quick Answer
Mitsubishi E6 means the communication link between the indoor and outdoor units has failed. These two units exchange data continuously on a 3-conductor communication wire (sometimes called the S1-S2-S3 or control wire). The most common cause is a loose or corroded connection at the terminal block inside the outdoor unit.
If you ignore an E6 and keep trying to restart the unit, you're not doing extra damage since the system won't run anyway. But don't let it sit for weeks. I've watched simple wire connection issues turn into full board replacements because moisture crept into a loose terminal and corroded the whole block. Catch it early and you're probably looking at a $0 repair and fifteen minutes of your time.
When I see an E6, I go straight for the S3 terminal first. Mitsubishi units use a DC voltage signal that rides on top of the AC power between the two units. If that signal gets noisy from a bad ground or a nicked wire, the whole system shuts down to protect the hardware. It's not a random glitch. It's the system doing exactly what it's supposed to do. And honestly, nine times out of ten it's a wire connection you can fix with just a screwdriver.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Loose or corroded connection at outdoor unit terminal block40%
Communication wire damaged by pests or weather24%
Indoor unit PCB failure22%
Outdoor unit PCB (control board) failure14%
Symptoms You May Notice
The indoor unit display shows E6 and the whole system just stops. No cooling, no heating, nothing, even if you mash the remote button ten times.
The operation lamp on the indoor unit blinks in a repeating pattern instead of staying solid.
You'll hear the outdoor unit try to start, maybe get two or three seconds into its startup sequence, then cut off completely.
System was working perfectly yesterday and stopped with zero warning, no gradual decline, no weird noises first, just dead.
In multi-zone setups, one zone throws E6 while the others keep running fine, which tells you the outdoor board is probably OK and the issue is in that one zone's wiring.
Can you reset a Mitsubishi minisplit to clear the E6 code?
Flip the high-voltage breaker for the outdoor unit off and leave it off for five full minutes. A quick 60-second toggle won't drain the inverter board capacitors completely. When you restore power, the indoor unit should go through its startup sequence and display the room temperature within about 90 seconds. If E6 comes back immediately, you've got a wiring or board issue that no amount of resetting will fix.
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
ComponentComponent Under Test
Expected Range0–5 ohms
ConditionIf Open (OL) or infinite, replace component.
Replacement Parts
If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.
Part Name
OEM Number
Estimated Price
Communication Wire (14-gauge 3-conductor)N/A - use 14 AWG 3-conductor wire · $15–$40
N/A - use 14 AWG 3-conductor wire
$15 – $40
Outdoor Unit PCB (model-specific)T7WE79178 (verify for your model) · $120–$350
T7WE79178 (verify for your model)
$120 – $350
Frequently Asked Questions
What wire connects the indoor and outdoor units on a Mitsubishi mini-split?
You need 14-gauge, 4-conductor wire including ground, usually called 14/4 mini-split cable or tray cable. The terminals are labeled 1, 2, and 3. Terminal 3 carries the actual data signal. Using thin thermostat wire or non-shielded wire is honestly the number one cause of intermittent E6 errors I see on DIY installs. It can't handle the voltage and it picks up interference from the compressor motor. If you're running new wire, don't cheap out here. The wire is like twenty bucks for a twenty-foot run and it'll save you a service call.
Can E6 be caused by a power surge?
Yeah, absolutely. I've seen plenty of cases where a nearby lightning strike or a utility transformer blowing fries the opto-isolator on the communication circuit. It's a tiny component on the PCB that handles the data handshake between the boards. Here's the frustrating part: if that happens, the board might still power up and look totally fine. All the indicator lights come on, it seems like it's working. But it'll never communicate with the other unit again. You need a new board. A whole-house surge protector is cheap insurance against this kind of damage.
My Mitsubishi E6 only shows up in winter. Why?
Cold metal contracts. When the terminal block gets cold, if the installer didn't torque those screws down tight enough, that tiny bit of contraction is enough to break the electrical contact on the S3 data line. I tell all my clients to get their terminal connections checked and retightened every fall before heating season starts. It's a five-minute thing during a maintenance visit and it prevents these cold-weather communication faults completely. If this is happening to you right now, try tightening the outdoor terminal screws when the unit's cold outside and it'll probably clear right up.
Can I swap the indoor and outdoor PCBs myself to diagnose E6?
I'd steer you away from that. Mitsubishi boards have specific dip-switch settings and jumper configurations that have to match your exact model and capacity. If you put in a replacement board without copying the exact settings from the old one, you can cause a permanent system mismatch or damage the compressor. It's not like swapping a car part where it either fits or it doesn't. You need the service manual for your specific serial number and you need to know what you're looking at before you start flipping switches on a board.
How much does it cost to fix an E6 error on a Mitsubishi mini-split?
If it's just a loose terminal screw, it's basically free. Tighten it and you're done in ten minutes. New wire run is maybe $50 to $150 in materials depending on how far the units are apart. An outdoor PCB replacement is where it gets expensive: the board itself runs $200 to $500 depending on the model, plus labor if you're not doing it yourself. Indoor PCBs are usually a bit less. Bottom line, always diagnose the wiring and connections before anyone starts talking about board replacements. That's the right call nine times out of ten and I've seen plenty of homeowners get talked into a new board when a ten-cent tightened screw would've fixed it.