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Generation 1, P1636 error

Discussion in 'Generation 1 Prius Discussion' started by John B., Jul 2, 2017.

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  1. John B.

    John B. Junior Member

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    Sorry, I did not see a Generation 1 forum. I have a 2003 Prius that has error code code P1636, indicating that the HV ECU is not communicating. Car was running and starting great before this. now it will not even attempt to start. The traction battery display indicates that the battery is down to one bar. I have cleared the error and the cat will still not start. The error code does return when I turn the ignition to the on position, so something is clearly bad.

    Has anyone replaced the HV ECU before? Are there any fuses or relays that could be causing the issue? could a low traction battery cause this error?
     
    #1 John B., Jul 2, 2017
  2. Brian in Tucson

    Brian in Tucson Active Member

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    Do you have the manuals?
     
    #2 Brian in Tucson, Jul 3, 2017
  3. John B.

    John B. Junior Member

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    I have a hayes manual, which does not cover the hybrid system very well.
     
    #3 John B., Jul 3, 2017
  4. ChapmanF

    ChapmanF Senior Member

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    In my 2001 manual, P1636 is a code reported by the Engine ECU, saying that it's having trouble communicating with the HV ECU. The troubleshooting steps are to pin down whether it's one or the other of those ECUs at fault, or the wiring between them. It's only two pages in the manual, but suggests an oscilloscope to eavesdrop on the HV-to-ECM pair and see if the HV ECU is making its usual chatter. (If it is, that's a sign the engine ECU is the one with an issue.)

    What are you reading codes with? There are a lot of generic scantools that are able to connect to the Engine ECU in a Gen 1 but not to the HV ECU, so you might only be getting one side of the story. If you were to connect with Techstream (or even with a ScanGauge II, Torque app, etc., if you load the custom NHW11 PID files), you might get an earful from the HV ECU also, and have a better idea what's going on.

    -Chap
     
    #4 ChapmanF, Jul 3, 2017
  5. ericbecky

    ericbecky Hybrid Battery Hero

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    The hv Ecu inside the battery case can have corrosion on that travels from the battery connections itself.
    Then the pins on the computer become corroded. I have even seen corrosion on the boards inside the Ecu.

    It's not fun getting to it, but it's a doable project. Just wear some high voltage safety equipment. Also be careful when torqueing down any of the small 8mm bolts. It's easy to overtorque or cross thread them.
     
    #5 ericbecky, Jul 3, 2017
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  6. ChapmanF

    ChapmanF Senior Member

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    Just a reminder that in Gen 1, the ECU inside the battery case is called the Battery ECU. The Gen 1 HV ECU is beneath the carpet at the front passenger's feet, while the Engine ECU (a/k/a ECM) is behind the glove box and to the right, and the P1636 is about those two, not the battery ECU.

    -Chap
     
    #6 ChapmanF, Jul 3, 2017
  7. ericbecky

    ericbecky Hybrid Battery Hero

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    Good reminder chap.
    I read this way too quickly.
    Gotta stop responding when I've been working such long days.

    Logging off and heading to bed!
     
    #7 ericbecky, Jul 3, 2017
  8. John B.

    John B. Junior Member

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    Okay, I haven't done anything on this for a while as the plan was to sell it until it wouldn't start. I don't have thousands of dollars in testing equipment, so I usually just replace what is logical and cheap. I replaced the ECU, the one on the floor board, and now my error is gone! Unfortunately, it still will not start. I don't get a ready light at all. Not really sure what to do next.
     
    #8 John B., Jul 21, 2017
  9. JAM2017

    JAM2017 New Member

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    John,

    I am kinda in the same boat but in a much worse situation than yours with my family owned Prius. They have a flooded Prius that has a wet HV ECU. They replaced it and it won't start because HV ECU and immobilizer ECU doesn't recognize each other. I think there is a procedure for the mating ritual the ECUs to establish the link again although it does not work for them. It won't hurt to give it a try though.

    James
     
    #9 JAM2017, Jul 21, 2017
  10. John B.

    John B. Junior Member

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    I know that there is a flashing processes that you have to do with a lot of ECUs when you install them, but that involves special equipment that I would not have. I thought that it was not necessary to flash the 2003 Prius ECU as long as you got the same ECU model number you were replacing.
     
    #10 John B., Jul 30, 2017
  11. John B.

    John B. Junior Member

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    Anyone have any suggestions? Pretty much lost on this one. Does the CPU need to be flashed? I never get the ready light, but the security light goes out, so I am assuming it recognizes my key. Are there any fuses or relays that could be causing the issue? At this point there are no errors, but the traction battery is down to one bar. Could that keep it from starting?
     
    #11 John B., Aug 3, 2017
  12. John B.

    John B. Junior Member

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    Okay, still looking for answers. I pulled the cap off of the output from the traction battery and tested across the leads and got zero volts with the key on and also in the start position, which leads me to think that their is something wrong with the HV battery CPU. No error codes at all. Has anyone had to replace one of these units? What are the symptoms of them being bad? Hate to keep throwing parts at things, but I don't have thousands of dollars in testing equipment either.
     
    #12 John B., Aug 5, 2017
  13. ChapmanF

    ChapmanF Senior Member

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    One of the things enclosed in the battery case is the System Main Relay, which is completely controlled by the Hybrid Vehicle ECU (that's the one under the carpet at the passenger's feet, not the Battery ECU inside the battery case). The Battery ECU has three wires to the SMR to monitor it, but the control of it is from the HV ECU.

    You will always measure zero volts at the output if the SMR isn't energized, and if the HV ECU does not think every single box is checked for safety to go READY, it will not energize the SMR.

    So, all signs still point to your HV ECU under the passenger carpet, just where the P1636 pointed in your first post. Not necessarily that the ECU is bad or needing replacement (ECUs can go bad, but it doesn't happen all that often), but at the very least it is unhappy about something and trying to tell you by codes that you might not see with a generic scantool, or there is some wiring or connection damage preventing it from communicating.

    Pinning that down is the same next step it was a month ago. I'd suggest starting by making sure you have a tool that can get codes from the HV ECU (lots of posts on here about "mini VCI", though that's not the only option), and see what codes you get. If you get no HV ECU codes, or even no connection to the ECU, then that will point more toward a wiring/communication issue, or the unlikely problem with the ECU itself. Otherwise, you look up the codes you get, and do what da book says.

    -Chap
     
    #13 ChapmanF, Aug 5, 2017
  14. John B.

    John B. Junior Member

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    Okay, I did replace the ECU under the floorboard and that took care of my error code P1636. I can not hear a click in the traction battery case when I turn on the key, but I never get a ready light or the car to start. Since I replaced the ECU and cleared the errors, I am assuming that the issue is somewhere beyond the ECU.

    My tester is a Innova 3160d. I am not sure what it is capable of reading on my Prius.
     
    #14 John B., Aug 5, 2017
  15. ChapmanF

    ChapmanF Senior Member

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    Just to make sure I'm following ... did you mean to write "can not hear a click and never get a READY light", or "can hear a click but never get a READY light" ?

    I assume you meant not, and.

    My working assumption at the moment is that it just doesn't see any codes from the HV ECU, and that's why, at first, the only code you could see was an engine code (any scantool can read those) that only meant "hey, something's up with that other ECU".

    An easy check, if you're not sure, could be to look through the list of HV ECU possible codes to find one you could easily cause (by unplugging something, say), then do that, and see if your Innova reads the code.

    Whenever you change an HV ECU, you have to turn the ignition ON (only ON) and let half an hour pass (put a charger on the 12 volt battery so it doesn't poop out part way), so the new HV ECU and the existing immobilizer can get acquainted. If that hasn't happened, it certainly won't let the car go READY. Have you done that?

    -Chap
     
    #15 ChapmanF, Aug 5, 2017
  16. John B.

    John B. Junior Member

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    I can now hear a click from the traction battery when the ignition is in the on position, and I do not get the error code. I could not hear a click before I changed the front ECU.

    I had no idea about leaving the key on for half a hour to mate the new ECU. I did leave it on for 15 minutes or so, but I was afraid to go much longer for fear of killing the batteries. Thanks for the input.
     
    #16 John B., Aug 5, 2017
  17. John B.

    John B. Junior Member

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    Update: I had the traction battery out of the vehicle, so I gave all the cells a quick charge, put it back in and let it sit with the key on for 45 minutes, which of course killed the tiny 12 volt battery. I put the 12 volt battery on the charger hit the key and it started right up.

    Chap, thank you very much for the insight. So glad to have the Prius running again!
     
    #17 John B., Aug 7, 2017
  18. John B.

    John B. Junior Member

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    Okay, more problems that I don't see on this forum. Now I am getting a new error code: P1600: 1. X Manufacturers control P16 computer and auxiliary outputs 2 ECM BATT Malfunction. Any clues what that means?
     
    #18 John B., Aug 22, 2017
  19. John B.

    John B. Junior Member

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    still having issues, and have no clue what to try next. The Error code P1600 is now gone, but the P1636 is now on all the time instead of randomly. Also, for some reason the engine cooling fans are both running whenever the car is in the on position. I completely removed the ECU under the floor on the passenger side and they still were running! Could a temperature sensor be going bad and that is stopping power from getting to the ECU?
     
    #19 John B., Aug 31, 2017
  20. John B.

    John B. Junior Member

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    I have an update and another issue. First off, the communication problem that I was having turned out to be a relay that went bad. It is the middle blue one in the small fuse box attached to the middle of the firewall. I believe it is labelled Hydro Motor 2. I tapped it with a screwdriver and the cooling fans shut down, and the prius started right up. Yahoo!

    Unfortunately, I am still getting the P1600 error code that indicates that the live 12 volt feed to the ECU in not getting voltage. ( P1600: 1. X Manufacturers control P16 computer and auxiliary outputs 2 ECM BATT Malfunction.) Everything I have read indicates that this keeps all the codes in the ECU after the car is turned off. Anyone have any idea where to start? The only thing I could find was something about it was to check the EFI fuse, which I did, even though it makes no sense to, because if it was bad the car wouldn't start, right?

    Hopefully the information about the relay will help someone else.
     
    #20 John B., Sep 25, 2017
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