B1497 - Communication Malfunction (Bus IC) - need help

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Starship_Enterprius, Jul 3, 2020.

  1. Starship_Enterprius

    Starship_Enterprius Active Member

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    Wasn't sure if I should start a new thread as there are lots of related posts here in Priuschat. But I've also seen replies in those thread saying to start another thread as they are old and will not be seen. So mods let me know or just merge with other thread and i'm ok with it.

    Anyway, i have had B1497 since winter but since it was stuck in heater position I postponed opening until summer. Finally opened the dash this week and sure enough all my all dampers/flaps (air inlet, air outlet, air mix) are stuck in 1 position. From the internet I found Toyota lists 2 causes:

    B1497 BUS IC Communication Malfunction
    1. Air conditioning harness
    2. A/C amplifier

    I checked all the fuses under the dash and in the engine bay, except the fuse inside the inverter and the connector to the compressor as the AC is working. As cold air blows until the engine warms, then the heat overcomes the cold. But the AC keeps on working and continuously blows ice cold air anyway, so obviously only the dampers are in the wrong positions

    I disconnected the Air mix servo, disassembled the unit, and tested the motor with a 9v battery (just to eliminate the possibility) and sure enough the motor is working, all gear teeth intact and turning. So those are out of the way.

    So here is where I need help, because my electrical knowledge is limited to testing fuses only LOL! The harness seems the next cheaper/easier to test. Google says one way to check is by sticking the positive of a multimeter into the harness and the negative into the car body. So...

    I tried sticking wire clips into the connector like this and testing with the multimeter and got nothing Servo connector.jpg

    But I wasn't also sure if the pin connected well, or I stuck into the wrong holes.
    So I disassembled the servo motor, identified the positive...
    Servo motor connectors.jpg
    and connected them to the harness so I was surer I had the positive terminal. So far I got nothing.
    Harness test 2.jpg


    So my question is, was my test good enough to conclude I need to replace the harness? Or did I need to have the car running to run the test? (LOL!...like I said, my electrical knowledge is quite limited).

    Any help would be appreciated. Thanks!
     
    #1 Starship_Enterprius, Jul 3, 2020
    Last edited: Jul 3, 2020
  2. ChapmanF

    ChapmanF Senior Member

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    See this post for an explanation of what you're looking at there. That harness isn't just wires, so I'd be a little cautious about how to test it.

    [​IMG]
     
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  3. Starship_Enterprius

    Starship_Enterprius Active Member

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    Wow, thanks Chapman. That explains why i saw the same wires connected to all 3 servos. Unfortunately i just changed my front brake pads and lubed all my brake pins (more than 2 hours disconnected batteries). So that battery reset trick is not going to work for me like the Prius C mentioned from your link.

    Hmm....I think it's time to get the amplifier tomorrow, see if i can pry it open (if possible) and eyeball anything burnt. Worse case i will just have to buy some used cheap amplifier.
     
  4. ChapmanF

    ChapmanF Senior Member

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    I don't know if your problem is the same as the person was having with the c.

    Your amplifier is actively reporting trouble codes to do with the servo harness. The person with the c did not seem to be getting trouble codes (if I remember right), it was just that the system seemed to lose track of where the servos were, and needed a power cycle to figure it out again. (Which could also totally be a problem with the harness, just some different problem that the amplifier doesn't recognize and have a code for.)

    I guess if you find an amplifier for cheap, it's worth a try to replace that first, just because it's so much less work than getting to the harness. (Oh, wait, you've already got the dash out. Nevermind...) But I'd give maybe even odds that the amplifier is healthy and telling you the truth and maybe that harness is the culprit.
     
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  5. Starship_Enterprius

    Starship_Enterprius Active Member

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    I agree... i'm just waiting for the amplifier I got from ebay. At only US$25 plus $16 delivery it was still cheaper than a new harness at US$82. The open dash was a non factor. I had that open in about 25 minutes, and could probably snap it back in 5.

    Something curious though after I made my order. I went back to the car and tried with the harness disconnected, and the codes didn't change. Since that didn't really prove anything (as the problem could still be the harness or the portion of the ampli circuit dealing with the harness), I tried with the ampli disconnected and something ran inside the engine bay which sounded like the compressor or the radiator fan. I didn't really take time to confirm tho as I switched off quickly. I was so shocked i wasn't even sure if I switched in accessory power mode only, or i actually stepped on the brakes and that thing ran instantly before the engine could start. I don't think that observation helps in my situation, but for a noob I just found that strange.

    Anyway, I will update once I get the part sometime around the 20th. Thanks
     
  6. Prius3 newbie

    Prius3 newbie New Member

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    Hi Starship, I bought my car about 8 months ago. Only recently I've noticed that my heaters are stuck on cold and dont go hot. I have the same fault codes u had. Only difference is urs was stuck on warm where mine is cold.

    I am planning to get at the actuators and test them, but couldn't find no diy videos. This is where I stumbled upon ur thread. Did the amplifier solve ur problem? Does the dash have to come out to check the actuators or can I get at them from under the dash. Also where is this amplifier located?

    Ur help would be much appreciated.

    Tia
     
  7. Starship_Enterprius

    Starship_Enterprius Active Member

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    Hi Tia. Sorry, replacing the amplifier nor replacing the harness didn't work for me. I'm guessing my problem goes much deeper. Maybe the communication bus, or worse. I suspect someone tried to boost my car while I was not around, and fried some electronics.
    Since this was getting beyond my noob abilities and I probably will be replacing within 2 years I gave up. I now simply open or close the dampers manually during fall and spring. I figure in the 2 years I have it, I only need to do that 4 times lol. But your case may be different so don't give up yet.

    The amplifier is just a couple of inches above the floor, to the right to the gas pedal (for left side drivers). It is held up by a single screw and is very easy to disconnect/replace. I'll see if i can post a picture of it later.

    For the lower actuator, you don't need to remove the dash. Just the glove compartment and some flimsy plastic in the foot well. There are threads here in Priuschat showing how to do it.

    The 2 upper ones does though, so I'll post my DIY files if I can find it. Stay tuned lol.
     
    #7 Starship_Enterprius, Dec 22, 2020
    Last edited: Dec 22, 2020
  8. Starship_Enterprius

    Starship_Enterprius Active Member

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    I pulled out the amplifier (don't worry, I never screwed it back so it was easy) and laid it over the gas pedal. It's quite dark in my garage, so I had to over expose:

    20201222_074602.jpg
     
    #8 Starship_Enterprius, Dec 22, 2020
    Last edited: Dec 22, 2020
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  9. Starship_Enterprius

    Starship_Enterprius Active Member

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    This is someones vid i followed to remove the dash (this is only if you want to replace the harness, or access the upper servos). I took screen shots and made a quick guide for myself which is why it went quickly for me. But Priuschat complains it is too large to upload. So just watch this a couple of times and you'll be ok.

     
    #9 Starship_Enterprius, Dec 22, 2020
    Last edited: Dec 22, 2020
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  10. Prius3 newbie

    Prius3 newbie New Member

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    Thank you for the quick reply.

    I am in the UK rhd so I'm assuming for me it will be on the right. Looks straight forward to get to the amp. Is the bottom servo to control the heat? I'm guessing one of the upper 2 servos controls air flow direction. All I need is warm air and air to hit the windscreen to stop it steaming up. So as long as I can accomplish that I will be happy for now lol. Is there any way to test the amp before I purchase 1 of ebay? I've already replaced the control unit on the dash as I was told that the fault code means theres an internal fault with control unit. Im now thinking maybe they meant the amplifier.

    Thanks
     
  11. ChapmanF

    ChapmanF Senior Member

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    The communication bus in question just is that harness, so if both that harness/bus and the amplifier that talks to it have been replaced, I don't think there's very much left. Whatever's still going wrong, when found, probably won't turn out to be "much deeper", but more likely something kind of forehead-smacky. (Do those things ever happen to you? They do to me.)
     
  12. Prius3 newbie

    Prius3 newbie New Member

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    forehead smacky does happen to me too.

    Starship thanks. Found the amp, very simple. On rhd drivers side left to the park brake. I also think u cant be far off to solving yours as u have done pretty much everything. Maybe a faulty part from Ebay?

    I noticed there seem to be 2 servos above that, I unscrewed the easiest 1 to get to and carried out a function test hoping it would wind back and forth. I dont know which flap it operates so activated all servos 1 by 1. No movement unfortunately.

    I managed to find target and actual data on my diagnostic machine. Actual pulse data for all the servo positions are maxed out. Way off compared to target data. So my thinking is if I'm pushing the buttons on the climate control and the target data is responding accordingly that means a pulse is being climate control to the amp. But no pulse from amp to servo maybe? My toes were starting to freeze so I called it a day otherwise I was hoping to check continuity of the wires from the amp to the servo.

    Btw, my names Mo lol tia meant thanks in advance
     

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  13. Starship_Enterprius

    Starship_Enterprius Active Member

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    Yes, the lowest flaps control the heat...you need to push those flaps open. You can reach those by removing the white air duct that bends down to direct heat to your feet. But you also need to detach the servo motor shown in your pics to disengage the gears. It's a bit tight tho, but there is a thread here in priuschat that describes how they removed the servo and the air duct.

    The top flaps control the upper air vents. If your getting air from them, you should be ok. Otherwise the entire dash has to come off. I just jambed a piece of wood to keep mine open for now.

    I kinda remember having similar readings. So I'm guessing those are the default values. I also tried to change the target values via tech stream and the actual values never changed. Since the harness I got was brand new, the amp is probably the problem (or the control unit which I haven't replaced like you). I did pry open the amp but could not detect any burnt parts. I also don't know how to test it either.

    But if you can find another prius and test by swapping amps, you might not have to do all of these. I highly doubt it's the harness.
     
    #13 Starship_Enterprius, Dec 23, 2020
    Last edited: Dec 23, 2020
  14. Prius3 newbie

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    I did remove the bottom servo (circled in pic) and torn the cog by hand but it didnt seem to make any difference to anything. Is this the 1 u are saying controls the heat?If it controls the heat maybe I need to let the engine warm up a bit more and try again. That's y I assumed it's probably for air recirculation flap.

    I have no air going to the windscreen so may be dash off job. But I will wait until I have tried another amplifier.

    Will keep u guys updated once I try it.
     

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  15. ChapmanF

    ChapmanF Senior Member

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    This harness isn't just wires: it contains the ICs at each servo connector end that recognize each servo's address and may be involved in remembering its position pulse count.

    I'm not sure offhand the best way to dive into troubleshooting a situation quite like you describe, but whatever ideas are in the Repair Manual about it are probably as good as any.
     
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  16. Starship_Enterprius

    Starship_Enterprius Active Member

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    Yes that's one.
     
  17. Starship_Enterprius

    Starship_Enterprius Active Member

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    I found my old HVAC diagram.

    I think I may have been mixing the 2 flaps. I did do both the top and the bottom the same day and is why I am getting confused.

    Do try waiting until your engine is fully warm before opening your dash as i kinda remember playing with the lower flaps and getting hot or cold air, before opening up the upper flaps. It could save you all the effort to make sure.


    Prius HVAC.png
     
    #17 Starship_Enterprius, Dec 23, 2020
    Last edited: Dec 23, 2020
  18. Prius3 newbie

    Prius3 newbie New Member

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    sorry for the late reply. Got interrupted by xmas and the new year. Hope everyone had a nice xmas and a happy new year!

    Thanks for the diagram, strange that for rhd the air mix solenoid position is same as lhd.

    The amplifier has arrived and I will be trying it tomorrow. However the part numbers are different. Pretty sure it has to be exact same part numbers?

    Starship another thing I thought of ur issue is could it be a coincidence that all 3 solenoids have packed up? Is there a way to remove the bottom solenoid and power it up with 12v to c if it actually works Chapman? Or a way to check a pulse/power coming to the solenoids from the connector with a multimeter?

    I dont have any wiring diagrams but would be nice to get hold of some so we can check what kind of readings we should have at the connector
     
  19. Prius3 newbie

    Prius3 newbie New Member

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    Hope everyone had a nice xmas and happy new year.

    I've posted a few replies but they dont seem to publish lately.

    Thanks for the diagram.

    My amp has arrived so will be trying it today. I have noticed the part number is different, surely I should have matching part numbers. If they dont match will it be an issue

    Also I was thinking it could be possible all 3 servos have packed up. Is there any way to test 1 by powering it up with 12v Chapman? Or any way of checking for power/pulse on the connector to the servo Chapman? Where could we get access to a wiring diagram to show what output should be
     
  20. Prius3 newbie

    Prius3 newbie New Member

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    Update.

    New amplifier is a waste of time due to wrong part no. Its bought up an error for no communication to ecu. However the original fault code is still current in there so I dont think the amplifier is the issue. I've removed lower solenoid and turned the flap cog fully clockwise ran the engine for a bit and have hot air (yaay).

    Will now attempt dash removal to get air hitting the windscreen as I'm in need to get it back on the road asap.

    What's baffling me is what else could it be? Something as simple as a fuse maybe?
     
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