P0A93 – Inverter “A” Cooling System Performance


By Reinier (Contact Me)
Last Updated 2020-12-14
Automobile Repair Shop Owner

CodeFault LocationProbable Cause
P0A93 Inverter "A" Cooling System Performance
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What Does Code P0A93 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.

Where is the P0A93 sensor located?

This image shows the location (circled) of the inverter and its dedicated coolant reservoir on a Toyota Prius application. Note though that the actual appearance and location of inverters and their coolant reservoirs vary between applications, so be sure to consult reliable service information to locate and identify components correctly. Failing to do this could result not only in costly mistakes but also in potentially serious personal injury and even death by electrocution if correct service procedures are not followed.

What are the common causes of code P0A93?

Common causes of code P0A93 are largely similar across all applications, and could include one or more of the following-

  • Coolant leaks through perforations caused by corrosion ruptured coolant hoses or coolant pump seals
  • Low coolant levels
  • Use of unsuitable or incompatible coolant
  • Failed, failing, or defective coolant pump and/or coolant pump motor
  • Overheating of the inverter assembly as the result of almost any failure in the coolant system
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors anywhere in the coolant system’s control and feedback circuits
  • Failed or defective coolant temperature sensors
  • Failed, failing, or defective coolant fan motor
  • Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced

What are the symptoms of code P0A93?

Common symptoms of code P0A93 are much the same across all applications, and could include one or more of the following-

  • Stored trouble code and one or more illuminated and/or flashing warning lights
  • In some cases, additional codes may be set and stored along with P0A93
  • Depending on the nature of the problem, fluid (coolant) leaks may or may not be present, or may not be immediately apparent
  • Depending on both the application and the nature of the problem, the vehicle may be immobilized to prevent damage to other components of the drivetrain
  • Depending on the nature and severity of the problem, the PCM may initiate a forced shutdown of the drivetrain that will persist until the fault is found and corrected