P0AC3 on Ford

Ford Escape(1 issue)

• Hybrid Inverter/Motor Electronics Coolant Pump (MECS Pump) Failure — "Stop Safely Now" Shutdown2005-2012

  The first-generation Escape Hybrid uses a dedicated electric coolant pump (the Motor Electronics Coolant System, or MECS, pump) to circulate coolant through the traction inverter and DC/DC converter — a loop entirely separate from the gasoline engine's cooling system. The brushed pump motor wears out and the pump stops circulating, so the inverter power electronics overheat. The hybrid control system responds by throwing a red-triangle warning and a "Stop Safely Now" message, which derates and then disables the vehicle, often at highway speed. Failures are typically intermittent first — the vehicle restarts and drives normally for days — before the pump quits entirely. Owners on escape-city and Ford forums report the failures beginning in the 50,000-mile range and repeating on a second pump. Because the loop is separate from the engine, the temperature gauge reads normal throughout and the engine never overheats, which sends many owners and shops down the wrong diagnostic path. Ford TSB 08-24-5 covers a related overheat pattern on 2005-2008 Escape Hybrid and 2006-2008 Mariner Hybrid. This is a hybrid-only failure on the 2.3L Atkinson hybrid powertrain; it does not exist on the conventional 2.3L or 3.0L Escapes.