Sector-specific climate actions are widely recognized for their air pollution co-benefits. However, uncertainties in cross-sector climate action may weaken or reverse these co-benefits. This study quantified the potential negative impacts of uncertain climate actions in the passenger car (PC) and power sectors on air pollutant (AP) emissions by integrating a fleet model with a power plant model under various infrastructure-level transition pathway combinations. Our results show that uncertainties in cross-sector climate actions, particularly when fleet electrification lags behind the car sector’s ideal transition pathway across all power sector transition scenarios, are projected to lead to a maximum increase of ∼120% in nitrogen oxide emissions and ∼635% in particulate matter emissions from the power and PC sectors in 2050, compared to maintaining the 2020 action levels. Additionally, the indirect AP emissions from the electricity use of electric cars are reallocated to provinces that rely heavily on coal-fired power, such as Inner Mongolia, Shanxi, Shandong, and Guizhou, along the power supply chain, thereby leading to significant losses in air pollution reduction co-benefits. We highlight the necessity of shifting from the current single-sector-oriented climate-mitigation policy framework to a cross-sector-integrated perspective. Specifically, it is crucial to reduce car use demand and enhance AP emission control for coal plants in the near term, while accelerating renewable energy transition in the power sector as a long-term strategy to effectively enhance air pollution control co-benefits in response to uncertainties during policy implementation.