check engine light + soft whirring noise

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Danica, Jul 30, 2026 at 6:22 PM.

  1. Danica

    Danica Junior Member

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    Vehicle:
    2007 Prius
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    Hi everybody,

    2007 Prius, just under 130,000 miles on it, still on the original hybrid battery, had the 12 volt battery and inverter pump both replaced last year. I live in the Coachella Valley where it is HOT right now.

    Last Wednesday, July 22, my check engine light came on just as I was returning from dropping off my broken cell phone at the phone repair shop. The phone was not fully fixed until Monday so I couldn't call my usual mechanic, but I did stop by Auto Zone to get the codes read. It showed the codes were P1121 and P1122. Indicating an issue with the coolant flow control valve.

    I drove the car on Friday and it was driving fine but that's when I noticed the soft whirring noise recurring constantly as I drove. The whirring noise lasts about 4 seconds and recurs about every 5 seconds. I did some internet searches and it seemed like the noise could be connected to the faulty coolant flow control valve.

    On Tuesday morning I finally dropped off my car at the mechanic shop. They called me later to confirm the problem was the coolant flow control valve, and he quoted me a total price of $930 to take care of it (including a $150 diagnostic fee). I agreed, and picked up the car this morning. But I have two problems:

    1. The invoice they gave me is inconsistent. Under Labor, it clearly says "coolant flow control valve, remove & replace" but under Parts it lists "engine auxiliary water pump" which -- according to several internet searches -- is definitely NOT the same thing.

    2. On the drive home, the car is still making the exact same noise as before!

    I did call the repair shop again (worth noting they are extremely busy these days) but I did not talk to the same guy I had been dealing with before, and he seemed confused. He tried to tell me that the coolant flow control valve and the auxiliary water pump are basically the same thing because they are part of the same system, but I'm not so sure.

    Can anybody out there help me understand what the heck is going on with my Prius?
     
    #1 Danica, Jul 30, 2026 at 6:22 PM
  2. ChapmanF

    ChapmanF Senior Member

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    IV
    That is what those codes were about.

    Ehhhh, maaaybe, but that valve usually sounds more like a washing machine agitating, or an old floppy disk drive seeking back and forth, if you're old enough to have heard that.

    Whirring for a few seconds and recurring every so many seconds would be a description much more often seen for the hydraulic pump in the brake actuator, which would be completely unrelated to the cooling-system parts. It's not at all unheard-of for a car to develop a couple different problems that really aren't related to each other.

    That also makes me lean toward thinking brake actuator. But you could make a recording and post a link.

    You're right to be skeptical. The gen 2 Prius engine cooling system is extra funky for the number of pumps it has: the belt-driven one, an electrical one at the coolant thermos, and yet another electrical one near the cabin heater core to keep the hot coolant flowing there when the engine is stopped. And there's also the flow control valve, which is not any of those other things.

    Also, the car has yet another electric pump that is mounted near the coolant control valve but has nothing to do with the engine cooling system at all. That pump is for cooling the inverter.

    So there are all kinds of things the shop might have replaced. Did the invoice show a part number?
     
    #2 ChapmanF, Jul 30, 2026 at 7:05 PM
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