2005 Prius – “Check connection to air conditioner” + can’t locate A/C amplifier (HVAC ECU)

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Gary Chan, Apr 27, 2026 at 4:55 PM.

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  1. Gary Chan

    Gary Chan New Member

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    Vehicle:
    2005 Prius
    Model:
    One
    I’m working on a 2005 Prius and getting the “Check connection to air conditioner” message on the MFD.
    Here’s what I’ve done so far:
    Checked all relevant fuses (A/C, ECU, HTR) – all appear good
    Removed the MFD and reflowed/soldered pin 60. This was shown on a youtube video on a Lexus LS430 2004.

    I also tested ground brown wire appears stable coming into MFD. The green wire to pin 60 appears to be data and carries no voltage. So, I'm not sure how to test it.

    Removed the radio/head unit to inspect wiring and look for the A/C amplifier (HVAC control ECU). Chat GPT said this is the next thing to check/swap.
    At this point, I’m trying to locate the A/C amplifier, but I haven’t been able to find it.
    I’ve checked:
    Driver side near the gas pedal area
    Passenger side near the blower motor / HVAC box. Passenger side carpet towards center console. Center console appears to have a semi-circular duct box and behind the the hvac box? Im unable to remove the semi-circular duct.

    I’ve searched PriusChat and YouTube but keep finding conflicting info or unclear locations. For example, there is a video showing the ac amplifier near gas pedal, or blower motor under glove box or on the passenger door foot area. But not clear for the 2nd Gen Prius.

    Main question:
    Where exactly is the A/C amplifier located on a 2005 Prius (Gen 2)? Is it buried deeper behind the dash or mounted somewhere less obvious?
    Also, if anyone has run into this specific MFD message before, I’d appreciate any guidance on what else to check.

    Thanks in advance.
     
    #1 Gary Chan, Apr 27, 2026 at 4:55 PM
  2. dolj

    dolj Senior Member

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    Vehicle:
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    So, you're chasing this down because of a message on the MDF, yes?

    The next step, then, is to read the codes your car has. You don't have a capable reader**? Don't worry, read your A/C codes by following the instructions >> here << on our blink code wiki.

    Tell us the blink codes or the diagnostic trouble codes (DTCs) you have pulled from the car. We can then give you much better advice than ChatGPT.

    You don't have a capable code reader? If it is your plan to repair your own car, then you need to have a reliable way of reading your DTCs. Read >> this post << which sums up the review thread to that point. Feel free to read the whole thread that starts >> HERE <<.

    The only reference I found in the repair manual that said anything similar to the phrase you quoted above is contained in the work-up for DTC B1262 – A/C ECU Communication Stop. Other references are in:
    • DTC – P3108-535 –A/C Amplifier Communication Circuit Malfunction
    • DTC – P3108-536 – A/C Amplifier Communication Circuit Malfunction
    • DTC – P3108-538 – A/C Amplifier Communication Circuit Malfunction
    You are aware that ChatGPT does not know everything, and when it comes up against such knowledge deficits, it just makes stuff up. It is far better to access the correct information directly from the Toyota Prius repair manual for your car. The most up-to-date information can be obtained at Toyota TIS (Technical Information System). You can read all about how to do that in this >> PC wiki article <<.

    If ChatGPT has not led you up the garden path, you can find the A/C amplifier ECU in the diagram below:

    Location of A:C Amplifier ECU.png




    ** If you tried to read the codes and your reader reported no codes found, you do not have a Prius-capable reader.
     
    #2 dolj, Apr 28, 2026 at 3:07 AM
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