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Severity: High Code type: Generic (all makes)

P0A93 Code: Inverter 'A' Cooling System Performance

The inverter's separate coolant loop isn't carrying heat away – usually a dead electric inverter coolant pump.

Safety first · Consult a professional

  • High-voltage system: hybrid/EV battery circuits (orange cables) can be lethal. Do not open or probe them — leave this to a trained EV technician.

At a glance

Severity: 4/5 – High4/5

Severity: High

Meaning
Inverter 'A' Cooling System Performance
System
Hybrid / EV · Powertrain
Safe to drive?
With caution
Typical repair cost
$30–$5,500
DIY difficulty
Moderate

The inverter turns the battery's direct current into the three-phase current that drives the motor-generators, and on Toyota-style systems the same box also holds the boost converter and the DC/DC converter that charges the 12 V battery. All that power electronics runs on its own coolant loop, separate from the engine: a small 12 V electric pump, a dedicated radiator section at the front of the car and a separate reservoir. P0A93 sets when the hybrid control module sees inverter temperatures rising faster or higher than the load explains, or detects that the pump isn't working. By far the most common cause is a worn-out inverter coolant pump, followed by low coolant in that loop. The inverter protects itself by cutting power, but running it hot for long can destroy it – which makes a cheap pump failure an expensive one.

How to read P0A93

How to read P0A93P102A3934
  1. P Powertrain
  2. 0 Generic (SAE)
  3. A Hybrid propulsion
  4. 93 Specific fault

Symptoms

  • Check engine light, red triangle and 'Check Hybrid System' message
  • Power cut back noticeably after a few minutes of driving, better after a cool-down
  • No coolant movement visible in the inverter reservoir while the car is in Ready
  • Faint hum from the inverter pump missing, or a grinding noise before it failed
  • Car shuts down in stop-and-go traffic on a hot day
  • Pink coolant drips or crusty residue near the front of the engine bay

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Worn-out or seized electric inverter coolant pump 45%
  2. Low coolant in the inverter loop from a small leak or neglected top-ups 18%
  3. Pump fuse, relay, connector or wiring fault 12%
  4. Air trapped in the loop after a coolant service or repair 10%
  5. Inverter radiator section blocked by debris or a kinked, collapsed hose 8%
  6. Faulty inverter temperature sensor or internal inverter fault 7%

Diagnosis step by step

Diagnostic flow: P0A931Check the reservoir while in Ready2Feel and listen for the pump3Watch inverter temperatures in livedata4Inspect hoses and the front radiatorstack5Replace the pump and bleed the loop6Clear the code and verify on a drive

  1. Check the reservoir while in Ready

    With the engine bay cool, find the inverter coolant reservoir (a separate tank, often marked for the inverter or hybrid system). Put the car in Ready in Park and look inside: on many Toyota hybrids you can see coolant swirling or rippling at the return line. A level below the mark or perfectly still coolant is your first clue.

    Tools: Flashlight

  2. Feel and listen for the pump

    In Ready, a healthy pump hums quietly and you can feel a light vibration on its body. Silence, a grinding noise or a hot pump housing with no flow points to the pump; check its fuse and the 12 V supply at the connector before condemning it.

    Tools: Multimeter, Flashlight

  3. Watch inverter temperatures in live data

    A hybrid-capable scan tool shows the temperatures of the motor inverters and boost converter. Parked in Ready they should sit close to the inverter coolant temperature; values that keep climbing past about 150 °F with no load mean the heat isn't being carried away.

    Tools: OBD-II scanner

  4. Inspect hoses and the front radiator stack

    Look for pink crust at hose joints and the pump, soft or collapsed hoses, and leaves or bugs packed between the A/C condenser and the inverter radiator section.

    Tools: Flashlight

  5. Replace the pump and bleed the loop

    The pump itself is a 12 V part and replacing it is within reach of a careful DIYer, but stay away from orange cables and never open the inverter cover. Refill only with the coolant type the manufacturer specifies and bleed the loop by running the pump in Ready and topping up until no bubbles appear; some models need a scan tool command to run the pump.

    Tools: Pliers, Towels & shallow pan, Gloves

  6. Clear the code and verify on a drive

    After clearing, drive 20 minutes including stop-and-go while watching inverter temperatures. They should stay stable and P0A93 should not return.

    Tools: OBD-II scanner

Repair options & costs

RepairDIY?Estimated cost
Top up and bleed inverter coolant Yes $30–$150
Replace inverter coolant pump Yes $250–$650
Repair pump fuse, relay or wiring No $60–$250
Clean or replace inverter radiator section No $250–$750
Replace overheated inverter assembly No $2,600–$5,500

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Toyota

Inverter coolant pump failure is a well-known problem on 2nd- and 3rd-generation Prius and other Toyota hybrids such as the Camry Hybrid. Toyota extended coverage on the pump for some Prius model years, so ask a dealer to check your VIN before paying for the part.

Field data

Toyota 4 Prius, Highlander Hybrid

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

The check engine light is on, so the car fails an OBD smog or emissions test. After the pump is replaced and the code cleared, allow a few drive cycles for readiness monitors before retesting.

Frequently asked questions

Is the inverter coolant the same as engine coolant?

Usually it is the same type of long-life coolant, but it runs in a completely separate loop with its own reservoir and pump. Topping up the engine side does nothing for the inverter.

Can I replace the inverter pump myself?

On many models, yes – it's a 12 V pump held by a bracket and two hoses. The real work is bleeding air from the loop afterwards. If you're not comfortable working near high-voltage components, have a shop do it.

What happens if I ignore P0A93?

The inverter keeps running hot, the car limits power more and more, and eventually the inverter or its boost converter can fail. That repair costs several times more than the pump.

Why did P0A94 appear too?

The boost converter shares the inverter's cooling. When it overheats, the converter can fault as well, so P0A94 alongside P0A93 is common and often clears once the pump is fixed – unless the heat already caused damage.

Sources