P1116 turmoil and a loose wire

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Jared Roth, Oct 6, 2025 at 1:42 PM.

  1. Jared Roth

    Jared Roth New Member

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    Hello all,

    I've got a 2009 prius with 225k in Oregon. I've got a persistent p1116 that will not go away. Heres the background on it. Last year I got the red triangle of death while driving and in limp mode I took it to the closest mechanic(which ended up being a big mistake). My memory is foggy but I recall it throwing P1121 and P1116 at that time. The mechanic said he owned a gen 2 and was sure it was the ECU. I was very dubious but I'm not a mechanic and he said he was sure. Quoted about $2000. I asked if he could go used and they did order and install a used one. Got it back, it threw the same codes on the way home. Took it back. He said it was the heater control valve, and replaced it. The p1121 cleared after that. But p1116 came up with sloshing noises being heard under the hood. I told them I thought air was in there and they tried THREE different times to clear it and the slosh finally went away. But p1116 came back soon after. They had my car on and off for 2 weeks and I had enough of them so I just started driving it. That was about 10,000 miles ago and other than than the CE light the car has driven great, no issues. Now its time for smog and its an automatic fail due to the CE. I took it to a new mechanic and he is saying its your inverter pump(very expensive). Before I throw another 1-2k dollars at this old girl, can I get some advice? *I'm guessing this is not related but I just found this loose wire with a... prius 1.jpg prius 2.jpg ring terminal that originates under the air filter housing. Any clue what it is? THANK YOU all!
     
    #1 Jared Roth, Oct 6, 2025 at 1:42 PM
  2. PriusCamper

    PriusCamper Senior Member

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    Any chance you're in the Northern part of Oregon? I'm a bit over an hour north of Portland and I can't stand to see people get overcharged a fortune for easy repairs and would like to help. I only charge $48 an hour for labor and online support is free.

    Alternatively, do you have a friend or family member who has experience working on cars? We could walk them through all the repairs...

    In the meantime, remove the plastic cover in front of the engine to reach the radiator cap and when the car is cold each time before you drive top off the coolant in the radiator and see if that addresses the sloshing sound you're hearing.

    I'll offer more replies once you reply...
     
    #2 PriusCamper, Oct 6, 2025 at 7:21 PM
  3. Jared Roth

    Jared Roth New Member

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    Thanks for your response! The sloshing/air has not occurred in a very long time as I mentioned. I'm an amateur mechanic and have the tools. If you have ideas I'd greatly appreciate them! Thanks again.
     
    #3 Jared Roth, Oct 6, 2025 at 10:32 PM
  4. Jared Roth

    Jared Roth New Member

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    ...and I live in Ashland, Oregon.
     
    #4 Jared Roth, Oct 6, 2025 at 10:32 PM
  5. Hayslayer

    Hayslayer Member

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    A P1116 has NOTHING to do with the inverter coolant system, so any mechanic telling you the inverter cooling pump is the culprit is lost or brain dead. If he's an experienced Gen 2 Prius guy, he's an embarrassment to the community. You already got railed for an ecu, get away from that guy asap. These codes are very BASIC and COMMON gen 2 prius stuff. You need to find a mechanic with a clue.

    The p1116 is for a problem in the coolant temperature sensor circuit of the engine/heat storage system. The p1121 is telling you there is a problem with the multiway valve that controls flow into and out of the heat storage system. Both of those systems are for the ENGINE cooling loop, not the inverter/electronics cooling loop. NEITHER will cause problems for actually driving the car.
     
    #5 Hayslayer, Oct 7, 2025 at 9:48 AM
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    The loose wire is an engine "ground". The ring terminal should be attached to the body somewhere near the radiator.

    The US spec Gen2 Prius has a Coolant Heat Storage system. When you turn the car off, it pumps a couple quarts of hot coolant into a thermos tank - which can keep it hot for 2-3 days.

    When you turn the car on the next day (or three), that still hot coolant is pumped back into the engine. This reduces engine warm up time - and cold run tailpipe emissions.

    The "3-way" coolant control valve (the part that usually causes P1121 code) directs flow in or out of the CHS tank.

    P1116 sets when the ECM doesn't like "something" about what it sees from the coolant temperature sensor at the base of the CHS tank. My first guess is that the CHS pump doesn't work - could be the pump itself, or the pump relay & wiring.

    Or it might be that the 3-way valve hoses are not hooked up correctly.

    You would need someone with a capable scantool to test the system. Does the pump run after shutdown and before startup? What does the CHS ("water outlet") temperature show vs Engine Coolant Temperature?

    FYI, these Gen2 have four coolant pumps. 1 mechanical on the engine, 1 electric for CHS, 1 electric for heater (all part of engine cooling system). Then there's 1 electric that's only for the separate inverter system.

    Posted via the PriusChat mobile app.
     
    #6 mr_guy_mann, Oct 7, 2025 at 11:08 AM
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    The loose wire is an engine "ground". The ring terminal should be attached to the body sheetmetal somewhere near the radiator.

    Yes, make sure that the engine cooling system is full - check the level in the radiator when everything is cold.

    The US spec Gen2 Prius has a Coolant Heat Storage system. When you turn the car off, it pumps a couple quarts of hot coolant into a thermos tank - which can keep it hot for 2-3 days.

    When you turn the car on the next day (or three), that still hot coolant is pumped back into the engine. This reduces engine warm up time - and cold run tailpipe emissions.

    The "3-way" coolant control valve (the part that usually causes P1121 code) directs flow in or out of the CHS tank.

    P1116 sets when the ECM doesn't like "something" about what it sees from the coolant temperature sensor at the base of the CHS tank. (Yes, there are specific criteria for what SHOULD be setting this code, but I have seen several cases where "the book was wrong").

    My first guess is that the CHS pump doesn't work - could be the pump itself, or the pump relay & wiring.

    Or it might be that the 3-way valve hoses are not hooked up correctly.

    You would need someone with a capable scantool to test the system. Does the pump run after shutdown and before startup? What does the CHS ("water outlet") temperature show vs Engine Coolant Temperature?

    FYI, these Gen2 have four coolant pumps. 1 mechanical on the engine, 1 electric for CHS, 1 electric for heater (all part of engine cooling system). Then there's 1 electric that's only for the separate inverter system.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, Oct 7, 2025 at 11:09 AM
    Last edited: Oct 7, 2025 at 11:16 AM
  8. mr_guy_mann

    mr_guy_mann Senior Member

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    True enough, but the OP needs the check engine light "off" in order to pass state inspection.

    Posted via the PriusChat mobile app.
     
    #8 mr_guy_mann, Oct 7, 2025 at 11:11 AM
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