Toshiba [01 - 04] fault codewhat it means and how to fix it

Toshiba publish detail code 04 under initial code 01 as an indoor to outdoor communication fault, noting that it includes the compressor thermostat, and they publish 05 in the same group as another indoor to outdoor communication row. On the initial code 03 group, 07 covers the same ground again. So communication between the two halves of the system is described in more than one place in Toshiba's table, which is worth knowing when you are trying to match what your unit is showing. The two halves of a split talk continuously over the connecting cable that runs with the refrigerant pipes, and on a Toshiba domestic split that cable also carries the power for whichever unit the mains does not reach: as standard the power cord goes to the outdoor unit and the indoor unit is fed from it over the three numbered cores, with a supply into the indoor unit offered as the alternative.

One supply, both units. So a communication fault here does not mean the outdoor unit has quietly lost power while the indoor unit carries on — if the supply were off, nothing would light up at all. What Toshiba's current service manual actually lists for the serial signal fault is, in order: defective wiring or mis-wiring of the connecting cable; the operation signal not being sent by the indoor unit; the outdoor unit not returning its signal when operation starts, for which the engineer checks the fuses on the inverter board; and the return signal stopping during operation, which the manual attributes to a protector in the outdoor unit opening — the high-pressure switch or a thermal relay — with the instruction to check the refrigerant amount or anything else that could cause high temperature or high pressure. That last cause is the one to hold on to, because it means a Toshiba communication code can be the outdoor unit protecting itself rather than a wiring fault, and it is why the manual says to check any other codes found at the same time.

The timing is also published: the indoor unit sends for a minute, waits three, sends again, and flashes the error a minute after that, so the code appears roughly five minutes after the outdoor unit stops answering. The thing that makes this code particular to Toshiba is the order of operations. Their technical handbook says not to turn the power off before reading the fault codes, because that clears the diagnostic memory; their current service manual says the codes survive a power cycle. You cannot tell which you have from the room, and on a communication fault the temptation to cycle the power is at its strongest, so read the code, write down both parts, and then try the power. If it clears and never returns, that was a transient. If it comes back, you now have the evidence. What remains after that is the connecting cable, which runs outside and is exposed to weather, rodents and anyone working on that wall, the fuses and protectors in the outdoor unit, and the control boards at either end.

1. 1

   Read and record the full code before touching the power.

   Toshiba’s technical handbook states that turning off the power supply before reading the fault codes clears the diagnostic memory; their current service manual says the codes are kept. You cannot tell which applies from the room, and on a communication fault this is exactly the moment people cycle the power and lose the evidence.
2. 2

   Note both parts of the code. Communication appears more than once in Toshiba’s table, so the initial code matters for matching it.

3. 3

   If nothing at all is working — no lights, no response to the remote — that is a supply problem rather than this code. Toshiba’s owner checklist for a unit that does not operate is the main switch, the circuit breaker, a power cut and the timer.

   If a breaker has tripped, reset it once only. A breaker that trips again has found something, and repeated resetting removes the protection rather than the fault.
4. 4

   Ask whether anyone has been working outside or on the electrics recently. A comms fault appearing straight after usually has a simple explanation, and a cable disturbed during other work is Toshiba’s first cause.

5. 5

   Look at the outdoor unit. If it is smothered by planting, a cover or debris, or has been running in strong heat, clear the space around it — a protector opening on high pressure is on Toshiba’s own list for this code.

6. 6

   Now try a power cycle, having already recorded the code. If it returns, call an engineer and hand over both the code and what you have eliminated.