P0A94

P0A94 is set when the DC/DC converter — the component that steps the high-voltage hybrid pack (200-650V depending on platform) down to 12-14V to charge the auxiliary battery and run accessories — is not performing to spec; the BECM monitors output voltage against commanded setpoint and trips P0A94 when the delta exceeds 0.5V for more than 5 seconds, when output current is below demand, or when internal temperature exceeds 110C. Cheapest-first diagnostic ladder: measure the 12V auxiliary battery voltage with the hybrid system READY — a healthy DC/DC converter holds the aux battery at 13.8-14.4V, and anything below 13.2V with hybrid READY confirms the converter is not contributing. Verify the aux battery itself is not the failure. Caveat: P0A94 will set within minutes of jump-starting a hybrid from another vehicle if the donor's alternator spikes the aux battery above 15.5V — it can damage the DC/DC converter's output stage, and Toyota specifically warns against jump-starting Prius FROM another car.

Vehicle-specific patterns: 2010-2015 Toyota Prius Gen 3 (ZVW30) — DC/DC converter integrated into inverter assembly, failure usually thermal from inverter coolant pump death (P0A93 + P0A94 paired); inverter assembly replacement P/N G9200-47241. 2011-2015 Chevrolet Volt — APM (Accessory Power Module) failure throws P0A94 with reduced propulsion; GM TSB PIE0398 covers APM replacement under extended warranty 8yr/100K. 2008-2013 Chevrolet Tahoe Hybrid / Silverado Hybrid 2-mode — APM failure on 2-mode platform. 2005-2012 Ford Escape Hybrid — DC/DC converter is a separate unit under the hood. Estimated repair: $680 to $3,200.