Skip to main content
Error code reference
Sub-Zero Refrigerator Error Code 20 4 42
Defrost system primary heater fault.
SourceSub-Zero Original (7011904): Prior to Serial 4100000: Service Manualp. 3-37
Diagnostic procedure
The full 20 4 42 procedure
Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.
MyPros+ · DiagnosticsStep 1 preview
1
First diagnostic step
Check defrost heater resistance (27.9-30.9 ohms); check wiring connections.
SourceSub-Zero Original (7011904): Prior to Serial 4100000: Service Manualp. 3-37
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
Unlock 20 4 42 procedure $9.95
Or subscribe: $29/month for all codes plus Max diagnostics, with 70 Max messages a day. Plus applicable tax.
Where this code is documented
1 manual in the MyPros+ library documents this code for Sub-Zero refrigerator.
Models covered by the manuals that document this code
- ICBBI-30U/O-LH
- ICBBI-30U/O-RH
- ICBBI-30U/S/PH-LH
- ICBBI-30U/S/PH-RH
- ICBBI-30U/S/TH-LH
- ICBBI-30U/S/TH-RH
- ICBBI-30UG/O-LH
- ICBBI-30UG/O-RH
- ICBBI-30UG/S/TH-LH
- ICBBI-30UG/S/TH-RH
- ICBBI-36F/O-LH
- ICBBI-36F/O-RH
- ICBBI-36F/S/PH-LH
- ICBBI-36F/S/PH-RH
- ICBBI-36F/S/TH-LH
- ICBBI-36F/S/TH-RH
- ICBBI-36R/O-LH
- ICBBI-36R/O-RH
- ICBBI-36R/S/PH-LH
- ICBBI-36R/S/PH-RH
- ICBBI-36R/S/TH-LH
- ICBBI-36R/S/TH-RH
- ICBBI-36RG/O-LH
- ICBBI-36RG/O-RH
More models are covered than are listed here.
75,000+ service documents · 20,000+ error codes · 100+ brands
Get Started$29/month · Cancel anytime · Or $9.95 3-day pass · Plus applicable tax