Do this before it fails. The inverter pump fails silently. When it goes, the inverter can overheat within minutes of driving. An overheated inverter is a $3,000–$5,000 repair. A new pump is $60–$200. This math is obvious.
What Is the Inverter Coolant Pump?
The Gen 2 Prius has two separate cooling systems:
- Engine cooling system — standard water pump, runs off the engine belt
- Inverter cooling system — a small electric pump that circulates coolant through the Power Control Unit (inverter/converter) and MG1/MG2 motor generators
The inverter cooling system is completely independent. It uses a small electric pump (sometimes called the "inverter water pump" or "EWP") located under the hood on the passenger side near the firewall. This pump runs continuously whenever the car is in Ready mode.
At around 100,000–160,000 miles, the pump's brushes or bearings wear out. When it fails, coolant stops circulating through the inverter. The inverter temperature rises. The car throws code P0A93 and a red triangle — or sometimes just shuts down.
Symptoms
- Red triangle warning light
- OBD2 code P0A93 (Inverter Cooling System Performance)
- Car may shut into failsafe mode on longer drives
- Audible change in the pump sound (grinding, whining) before total failure
- Sometimes: no symptoms at all until complete failure
Parts
| Part | Cost | Notes |
|---|
| Inverter coolant pump (OEM Toyota) |
$150–$200 |
Toyota part # 16363-21010 or 16363-21020. Worth the OEM price on this one. |
| Inverter coolant pump (aftermarket) |
$60–$100 |
Several reputable aftermarket options exist. Quality varies — avoid the cheapest ones. |
| Toyota SLLC coolant (pink) |
$15–$25/gallon |
You'll lose some coolant during the swap. Have this on hand. |
| Hose clamps (optional) |
$5 |
Replace if the old ones look corroded or weak. |
Only use Toyota Super Long Life Coolant (pink/red). The inverter cooling system uses a different coolant than the engine. Mixing types causes gelatinous deposits that destroy the pump and inverter. Do not substitute standard green or orange coolant.
What You'll Need
- 10mm socket and ratchet
- Flathead screwdriver (for hose clamps)
- Drain pan
- Funnel
- Toyota SLLC coolant (pink)
- Shop rags
Step-by-Step
- Let the car cool completely. Even though this is the inverter system (not the hot engine coolant), give it 30 minutes after driving.
- Open the hood. The inverter coolant pump is on the passenger side, close to the firewall, near the inverter/PCU. It's a small black cylindrical pump with two coolant hoses and an electrical connector.
- Locate the inverter coolant reservoir — a small overflow tank usually near the pump. Note the coolant level before draining.
- Place a drain pan under the pump area. Loosen the lower coolant hose clamp and slide the hose off — coolant will drain out. Have rags ready.
- Disconnect the electrical connector from the pump (press the tab and pull).
- Remove the upper hose the same way.
- The pump is held with 2–3 bolts (10mm). Remove them and lift the pump out.
- Install the new pump in the same position and orientation. Bolt it down snugly — don't overtorque.
- Reconnect both coolant hoses. Make sure the clamps are tight and seated past the bead on the hose barb.
- Reconnect the electrical connector.
- Refill the inverter coolant reservoir with fresh Toyota SLLC coolant. Fill slowly — the system needs to purge air bubbles.
- Start the car in Ready mode. The pump should run immediately — you can hear it. Check for leaks around both hose connections.
- After 5 minutes running, recheck the coolant level and top off if needed.
- Clear any OBD2 codes and do a short test drive.
Bleeding the System
After refilling, air bubbles can get trapped in the inverter cooling circuit. The system usually self-bleeds over a few drive cycles. To help it along:
- With the car in Ready mode, gently squeeze the coolant hoses to work air bubbles toward the reservoir
- Top off the reservoir as needed
- After your first 2–3 drives, check the coolant level again and top off if it dropped
Toyota Recall / Technical Service Bulletin
Toyota issued recalls and TSBs related to the inverter coolant pump on Gen 2 Prius vehicles. If you haven't already, check whether your VIN is covered before paying out of pocket:
Check your VIN first. Some owners had this repair covered fully or partially under a Toyota recall or goodwill warranty extension. It takes 2 minutes to check and could save you the full repair cost.
Notes from the Field
March 23, 2013: Engine warning light came on while driving around 7PM. Brought the car into Lipton Toyota the next morning at 1PM. Diagnosed as the hybrid water pump showing signs it could fail. Total repair cost: $307. Parts alone were $50–$120; labor and shop time made up the rest. Repair took 75 minutes.
This is the repair that genuinely earns its preventive label. At 100,000 miles, replace this pump regardless of whether anything seems wrong. It's the same logic as replacing a timing belt — you replace it on schedule, not when it snaps.
The pump makes a faint hum when running normally. If you start hearing grinding or the hum becomes loud and labored, the pump is on its way out. Don't wait for the red triangle — by then you may have already overheated the inverter.
The OEM Toyota pump is worth the extra $50–$80 over cheap aftermarket options. This is a part that runs continuously whenever the car is on. This is not the place to save $50.