ODU E2 Indoor / outdoor communication error (outdoor board)

What the control is telling you

Outdoor board display. Indoor shows EL01 (old indoor E1).

Applies to: DLCMRBH / DLCMHBH multi-zone outdoor units 18-48K (Midea, Carrier, Viessmann Vitocal 200-S)

Test and repair steps

1. Safety kill power at the disconnect and wait for the inverter capacitors to discharge before touching boards or wiring.
2. Cycle power at the breaker. If the code clears, watch it for a while.
3. Check L1, L2, S and ground between outdoor and each indoor terminal block against the diagram. The S wire is polarity sensitive. Use 14/3 stranded with ground, never thermostat wire.
4. With the unit on, put the red lead on terminal 2 (L2) and black on S (or terminal 3) at the outdoor unit. A healthy line swings back and forth between + and - DC. Stuck positive = outdoor board side. Stuck near zero = indoor side.
5. Press the outdoor check button (SW1) once: the display shows how many indoor units are talking. Compare with the number installed.
6. Check the IPM board LEDs and the main board LED are lit, and that the reactor wiring is tight.
7. Swap parts in this order based on what you found: indoor PCB, IPM board, outdoor main PCB.
8. In high EMF areas a 14/2 shielded cable can replace L2 and S, shield grounded at the outdoor unit only.

Models that show this code

7 models in Viessmann Vitocal 200-S DLCM(R/H)B multi-zone outdoor

Other codes on the same units

• ODU -- Outdoor board standby
• ODU 00 Wiring / piping check finished
• ODU CE Automatic wiring / piping check running
• ODU E0 Outdoor EEPROM error (outdoor board)
• ODU E3 IPM to main board communication error (outdoor board)
• ODU E4 Outdoor or T2B sensor fault (outdoor board)
• ODU E5 Over or under voltage (outdoor board)
• ODU E6 PFC module protection (outdoor board)