Goodman Furnace E4 Error Code - Open Primary High Limit Switch

What Caused This Error?

The control system reports E4 when the monitored condition described by the error code is outside the expected operating range. In this case, the most likely trigger is clogged air filter. Other common contributors include blower wheel covered in dust or animal hair and blocked return ductwork.

Step-by-Step Diagnostic Check

1. Replace air filter immediately with correct size.
2. Inspect blower squirrel cage wheel and clean fins with wire brush.
3. Verify all dampers and floor registers are fully open.
4. Disconnect electrical power before opening panels. Measure limit switch continuity when cool; replace limit switch if open.