P0A0F

P0A0F is set when the hybrid control module commands an engine start sequence but the engine fails to crank or fails to achieve self-sustaining combustion within the calibrated window (typically 2-3 seconds on Toyota HSD, 1.5 seconds on Ford eCVT). The cheapest-first ladder starts with a scan-tool live-data check: confirm MG1 RPM during the start attempt (should ramp to 900-1100 RPM on Prius Gen 2/3; below 500 RPM points to MG1 resolver or inverter), then verify HV battery voltage stays above 180V on Gen 2 NHW20 or 200V on Gen 3 ZVW30 during cranking (sag below those thresholds means a weak module pulling the pack down). Next, pull the engine-side codes — P0A0F rarely lives alone, and a companion P0335 (crank sensor), P0340 (cam sensor), P0171 (lean), or P0420 will tell you whether the failure is electrical-spin or fuel/spark/compression. Caveat: on Prius Gen 2 with 150K+ miles, a tired HV battery can throw P0A0F intermittently on cold mornings without setting P0A80 — the pack has enough voltage at rest to pass isolation but sags under MG1 cranking load.

Vehicle-specific patterns: 2004-2009 Toyota Prius Gen 2 (NHW20) — weak HV battery module (one of 28 NiMH sticks) sags during MG1 cranking; check Techstream block voltages, any block reading 0.3V below the pack average under load is the culprit. 2010-2015 Toyota Prius Gen 3 (ZVW30) — inverter MG1 IGBT failure causes failed-start with companion P0A94/P0A1A; TSB T-SB-0090-14 covers inverter assembly replacement. 2013-2018 Ford Fusion Hybrid / C-Max — BECM software calibration bug throws P0A0F after deep discharge from extended sit; Ford TSB 18-2079 reflashes BECM. 2011-2015 Chevrolet Volt — 12V auxiliary battery weak (below 11.8V resting) prevents HPCM2 wake-up and aborts engine-start request. Estimated repair: $180 to $4,200.