In brief
Fault code 04 on Toshiba Seiya / Shorai / RAV means: Code 04 is the most common fault on Toshiba units. It indicates a missing signal on the serial communication line (terminal S3) between the indoor unit and the outdoor unit. Most common cause: Incorrect wiring (Phase/Neutral/Communication reversal), cut or loose S3 cable, outdoor unit MCB tripped (while indoor unit is powered), or blown PCB fuse. First action: Ensure both the indoor unit AND the outdoor unit are powered on.. Call a registered engineer if the fault returns after basic checks or involves refrigerant work (F-Gas registered engineer required).
According to the Toshiba Service Manual, a simple MCB reset is often sufficient if the outdoor unit restarts more slowly than the indoor unit after a power cut.
04 • Toshiba • Seiya / Shorai / RAV
Toshiba fault code 04: Serial communication fault (S3 link)
Code 04 is the most common fault on Toshiba units. It indicates a missing signal on the serial communication line (terminal S3) between the indoor unit and the outdoor unit.
Source: Toshiba Service Manual - Digital Inverter & Residential Split
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What does fault code 04 on Toshiba mean?
Code 04 is the most common fault on Toshiba units. It indicates a missing signal on the serial communication line (terminal S3) between the indoor unit and the outdoor unit.
Incorrect wiring (Phase/Neutral/Communication reversal), cut or loose S3 cable, outdoor unit MCB tripped (while indoor unit is powered), or blown PCB fuse.
Symptômes
- Air conditioning does not start
- The flap opens then closes without blowing air
- LED flashing (Operation/Timer) depending on model
- Code 04 on the wired remote controller
Diagnostic
1. Check power supply
- Ensure both the indoor unit AND the outdoor unit are powered on.
- Check that the MCBs have not tripped.
2. Check interconnection wiring
- Verify the connection on terminal 3 (S3) at both ends.
- Ensure there are no splices in the interconnecting cable.
- Check cable continuity.
3. Diagnose electronic PCBs
- Check the fuses on the indoor and outdoor PCBs.
- Measure the voltage between terminals 2 and 3 (fluctuating DC) to confirm signal transmission.
How to reset fault code 04 on Toshiba?
Restore S3 cable continuity or reset the outdoor unit power supply. If wiring is correct, replace the electronic PCB (often the outdoor one).
When should you call an F-Gas engineer?
Common after a mains power cut or when multiple units are powered on simultaneously.
Affected models
- Digital Inverter
- Residential Split
Field context
Common after a mains power cut or when multiple units are powered on simultaneously.
Technical source data
The Toshiba 04 fault indicates a communication error between indoor and outdoor units at startup. A simple MCB reset is often sufficient if the outdoor unit restarts more slowly than the indoor unit after a power cut.
Questions fréquentes
Why do I get error 04 after a power cut?
If the outdoor unit restarts more slowly than the indoor unit, the signal is delayed. A simple MCB reset is often sufficient.
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