Why Is Your Prius' Check Engine Light On?

If you drive a late-model Prius and the check engine light just came on, it's not time to panic just yet. Check engine lights can typically indicate any number of issues, and the most common error codes are rarely expensive. With early generation Priuses, cooling system-related failures are one culprit you can expect to see.

Which Trouble Codes Indicate a Cooling System Problem?

If the check engine light is on in your Prius, your first step should be to read the OBD-II trouble codes from the computer. You can do this yourself with a cheap tool, or you can have an auto parts shop or mechanic read the codes for free. The OBD-II specification lists many possible cooling system error codes, but P0A93 and P1121 are typical when dealing with older Priuses.

Code P0A93 is specific to hybrid models since it relates to the inverter water pump. The inverter on a hybrid vehicle is what allows your high-output batteries to power your electric motors without destroying them. This component requires an independent cooling subsystem, including a separate water pump.

Note that P1121 is another code that can have various manufacturer-specific meanings. For example, many manufacturers use this code to indicate a throttle position sensor issue. On the other hand, Toyota uses this code on the Prius to alert you to problems with the coolant control valve. This valve directs coolant between your engine, hot tank, and interior heater core.

What Can You Do to Clear Your Check Engine Codes?

Issues with the inverter cooling system are potentially severe, so you should never ignore a P0A93 code. Although this code triggers when your inverter's water pump shuts down, this doesn't always mean a pump failure. Other potential causes include coolant hose failures, wiring issues, and a system that requires bleeding.

On the other hand, you will almost always need to replace your 3-way coolant valve if you receive code P1121. Fortunately, this is a less critical issue than an inverter cooling failure. Although a stuck 3-way valve will impact your vehicle's overall efficiency and likely cause you to fail any emissions tests, it won't leave you stranded or cause additional damage.

In either case, you should have your vehicle diagnosed by a professional. Since both of these codes are manufacturer-specific, working with a mechanic with experience on Priuses is usually the best option for an effective and permanent fix.

If you need Prius engine repair, contact a local auto service.