Climate models reproduce sea surface temperature (SST) variability of El Niño/Southern Oscillation (ENSO) despite systematic feedback errors. Atmospheric feedback in response to ENSO’s SST anomalies remains biased even in atmosphere-only simulations, but the reason therein is unclear. This study focuses on atmospheric internal processes to reveal ENSO feedback biases common to the atmosphere-ocean coupled historical and atmosphere-only simulations of CMIP6. The net heat flux feedback becomes comparable to observations once the observed SST is prescribed, but the central Pacific zonal wind feedback is yet underestimated albeit a realistic equatorial precipitation-SST relation. The wind feedback bias is attributed to the wind responses to the equatorial precipitation anomalies that seasonally erroneously decline in boreal late winter, common to both the coupled and atmosphere-only simulations. The model’s mean state with peak-reduced and broad deep convective areas is favorable for enhancing the wind-precipitation relation and thus ENSO dynamic feedback.