P0A16

P0A16 is the circuit-high variant of P0A14/P0A15: the engine mount control actuator command line is reading above the expected operating voltage when it should be commanded low or off, or the feedback signal is pegged above the operating window. Circuit-high faults on a low-side-switched actuator (the typical configuration for active mounts) mean either a short to 12V on the command wire (chafed harness against a battery cable or a starter feed), a failed open driver FET in the ECU stuck pulled-up by an internal protection circuit, or a feedback sensor that has shorted to its reference voltage rail. Diagnostic ladder: unplug the actuator at the mount, key-on-engine-off, and measure the command wire voltage at the connector with a DMM (should read near 0V on a normally-de-energized line; reading 5V or 12V points to a short to power upstream). With the actuator unplugged, clear the code and see if it returns immediately (returns instantly means the short is upstream of the actuator); if it does not return immediately, the actuator itself was shorted internally and reading back to the ECU. Ohm the actuator solenoid (5-15 ohms healthy; a dead short reads near 0 ohms and is the most common circuit-high root cause on a high-mileage Prius mount). DO NOT probe HV orange-wire circuits with a standard multimeter. Always service HV with Class 0 1000V gloves, isolation tester (Megger), and DC-rated lugged probes; the HV interlock loop drops pack contactors at service-plug removal and must never be bypassed.

Vehicle-specific patterns: 2010-2015 Prius Gen 3 throws P0A16 most often from a shorted internal solenoid in the active mount itself after the hydraulic seal fails and fluid contaminates the coil; the failure usually progresses from P0A14 (performance) to P0A16 (circuit-high) over a few thousand miles, so a customer presenting with P0A16 often has older P0A14 history. 2012-2015 Prius Plug-In shares the mount and the progression. 2007-2017 Camry Hybrid and 2011-2017 Highlander Hybrid throw the code with the same internal mount short pattern. 2005-2012 Ford Escape Hybrid is a less common P0A16 vehicle and when it sets the code the harness short to a starter feed is the more likely root cause than a shorted mount. Estimated repair: $400 (mount) to $1,100 (mount + harness + ECU driver test).