What does it mean?
OBD II fault code P0A93 is a generic trouble code that is defined as “Inverter “A”* Cooling System Performance”, and is set when the PCM (Powertrain Control Module) detects a failure of the cooling system that serves the inverter assembly on hybrid vehicles. Note that hybrid and electric vehicles typically have several discrete cooling systems that each serve a different part of the vehicle’s drive train.
In the case of the inverter assembly, the cooling system is completely separate and independent of all other cooling systems. * Note that some hybrid vehicles have a second inverter, usually labeled “B”, which is used to maintain the charge in the 12V battery that powers the headlights, A/C compressor, and some other accessories.
The purpose of inverters on hybrid and electric vehicles is to convert the DC (Direct Current) electrical energy stored in the HV (High Voltage) battery pack into three-phase AC (Alternating Current) electrical energy for use by the MG (Motor/Generator) unit(s) that provides the motive power for the vehicle.
Since the conversion process generates relatively high temperatures that typically do not correlate with the temperatures of other parts of the drivetrain, the inverter assembly is provided with a dedicated, PCM-controlled cooling system to regulate and control the inverters’ internal temperature.
In practice, this cooling system consists of a dedicated water pump, as well as other dedicated components that include temperature sensors, coolant level indicators, thermostat(s), and hoses, although the inverters’ cooling system may share a section of the main radiator that is fitted with dedicated cooling fans. Note also that due to the materials used in its construction, the coolant used in the inverter assembly differs from coolants used in other dedicated cooling systems.
In practice though, the coolant used in the inverter’s cooling system has a finite service life, and failure to replace coolant according to the prescribed service schedule can cause acidification of the coolant, which can, in turn, cause fluid leaks in the system as the result of excessive or accelerated corrosion in the system.
Nonetheless, since the inverter assembly’s correct functioning is critically important to the safe and efficient operation of any hybrid or electric vehicle, the PCM monitors several parameters and operating conditions of the inverter’s cooling system continuously. These include, but are not limited to, the min/max temperatures of the coolant, coolant level, the current draw, and speed of the coolant pump, as well as the current draw and speed of the coolant fan.
If the PCM detects any deviation in the measured values of any parameter (from specified values) that exceeds a predetermined level or threshold, it will recognize that one or more defects are present in the coolant system, and it will set code P0A93 and illuminate one or more warning lights as a result.