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2007 Prius won't go into ready mode

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Sean I., May 16, 2024.

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  1. Sean I.

    Sean I. Junior Member

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    2007 Prius
    Model:
    LE
    While driving to a store a couple days ago, all of a sudden the master warning light (red triangle) and brake system warning light came on. I parked the car and when grocery shopping. Came back and couldn't start the car, even with portable battery jumper. Disconnected the battery and waited a while, reconnected, and car starts fine. While driving back home, the red triangle and brake system warning light comes back on. Since then, I'm not able to start the car into ready mode unless I disconnect the battery and reconnect it.

    I've had some issues already present with my 2007 Prius with 130k miles:

    - had catalytic converter stolen in 2022, replaced it with cheap one bought from Amazon (passed emissions test)
    - I've been having trouble starting the car sometimes. Thought it was the battery, but was able to start the car using portable battery jumper.
    - TPMS warning light on: a mechanic who looked at it while doing state safety inspection said TPMS sensors are fine, and the problem might be with ECM
    - Front brake pad and rotors were replaced a couple days ago. Also parking brake cable was adjusted at the pedal, not at rear wheels.
    - CEL on: P1116, P0138, P0037; used generic OBDII reader, not mini VCI.
    - I have been sitting on CEL for years after I had P2601 (replaced coolant pump, CEL went away, came back 6 mos later. I heard coolant pump is a long standing issue for Gen2 Prius but it isn't essential in operating vehicle to I didn't bother. I'm not sure how long above 3 codes have been on.

    I searched through the forum and tried the following:

    - installed a new battery, but problem persists. Red triangle and brake system warning light comes back on and car only starts after battery is disconnected and reconnected.
    - I thought it might have something to do with recently changed brake pads and rotors. Brakes work fine. Brake light comes on when I press the pedal.
    - Key Fob battery seems ok too. I will replace it tomorrow just to be sure.

    Can anyone shed some light on this issue? What is my next move?
     
    #1 Sean I., May 16, 2024
    Last edited: May 16, 2024
  2. dolj

    dolj Senior Member

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    Your symptoms seem to describe P0AA6 fairly well. You need to get a better code reader to confirm – one that can read the HV control and battery ECUs in particular.

    This wiki article reviews several Bluetooth VCIs and their associated apps.

    Gen2 OBD2 app review
     
    #2 dolj, May 16, 2024
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  3. Brian1954

    Brian1954 Active Member

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    ^+1
    You need a code reader which can read the main trouble codes and the INF detail code like the Autel AP200.
     
    #3 Brian1954, May 16, 2024
  4. Danno5060

    Danno5060 Member

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    TPMS only:

    One of the TPMS batteries finally gave out in my Gen 3. It would work for most days, but I think it was when the weather got colder that it failed to provide enough power. In my case, the dash light would flash, then go to solid, indicating it was a TPMS sensor problem. It may be time to replace yours, but of course, read the codes out of the TPMS system to see what the real problem is.
    ​
    Read the codes out of the ABS brake controller. Since that light is on, maybe that's trying to tell you something. Especially since you recently had brake work done. Check the brake fluid reservoir. Is the fluid almost clear, or cloudy and brown? Did they flush the old brake fluid as part of the service?

    I'm confused about the parking brake adjustment. I guess the cables could stretch, but I think most of the adjustment in the wheels comes from the self-adjusters in the rear drum brakes. As they function, it also looks like they would tighten up the parking brake too.

    How were the rear drums and rotors?

    When I first bought my Gen 3, it did have some engine starting issues. The wiring to one of the oxygen sensors was pretty chewed up. I don't remember what codes it had, but it was related to the O2 sensor. After I replaced it, I've had no problems with starting, and that's been about a decade ago. Fixing your O2 sensor, or the wiring may cure 2 of the three codes as well as the engine starting issues. I'm sure when they stole your cat, they didn't do your O2 sensor wiring any favors either.
     
    #4 Danno5060, May 16, 2024
    Last edited: May 16, 2024
  5. dolj

    dolj Senior Member

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    If the sensors are indeed fine, then one of the tire pressures must be off - the ECM fails very rarely, and I'm not even sure if the ECM is responsible for monitoring the tire pressures. Pretty sure there is a TPMS ECU. Check all tires and pump them up (MR is 35 PSI front/ 33 PSI rear). If you still have the light after this, do the tire reset procedure to reset the TPMS to what the tires are now. The procedure is in the owner's manual.

    The other three engine codes you mentioned are minor (and are relatively easily resolved) at this point if you have a P0AA6 so you should confirm this before making any decisions.
     
    #5 dolj, May 16, 2024
    Last edited: May 16, 2024
  6. Sean I.

    Sean I. Junior Member

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    I do check tire pressure once a week, and the pressure has been fine. I will try the reset procedure. Thank you!!
     
    #6 Sean I., May 17, 2024
  7. Sean I.

    Sean I. Junior Member

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    The mechanic who did safety inspection told me the TPMS sensors are fine. But I think I will double check with local tire specialist.

    As for the front brake pads and rotors, I installed them myself, but didn't bother with brake fluid condition. I ordered some stuff on Amazon to flush the brake fluid. I wonder if that will improve anything. I did not check the condition of rear drums and rotors.

    I also ordered the Denso downstream O2 sensor from Amazon since it seems rather simple part to replace. I will replace this Saturday to see if it changes anything.
     
    #7 Sean I., May 17, 2024
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  8. Sean I.

    Sean I. Junior Member

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    I'm dreading that I might have P0AA6, but cannot confirm since I do not have Techstream. Still looking online to see what my best option is. The code reader I have is Autel AL529HD (
    ) and I assume this one won't catch any issues with hybrid battery.
     
    #8 Sean I., May 17, 2024
  9. Sean I.

    Sean I. Junior Member

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    New development: the car still won't go into ready mode, except there are NO other lights on on the dash except CEL. Won't go into drive or reverse. After I clear the codes using the OBDII reader, car does go into drive mode, but still no dash lights except CEL. "Problem" on the LCD screen with red car icon. What is happening..... *sigh*
     
    #9 Sean I., May 17, 2024
  10. Brian1954

    Brian1954 Active Member

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    You need to buy a Prius capable scan tool to read ALL the trouble codes. See post #2 and #3.
     
    #10 Brian1954, May 17, 2024
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  11. Danno5060

    Danno5060 Member

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    You shouldn't need any specific flush. Suck out the old brake fluid out of the master cylinder, top it off, and bleed the slave cylinders till you're getting fresh brake fluid out.

    But that's not important right now...
     
    #11 Danno5060, May 17, 2024
  12. Sean I.

    Sean I. Junior Member

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    Agreed. I ordered Autel AP200 yesterday and it should be here in two days. Like dolj said, I'm afraid I might have P0AA6 given the symptoms and the posts I've been reading up on. Thank you all for your inputs, truly appreciated. I'll share the codes once I have them.
     
    #12 Sean I., May 17, 2024
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  13. Sean I.

    Sean I. Junior Member

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    So I did get a bluetooth OBDII scanner (Veepak from Amazon) and did a scan. It did throw P0AA6 among others (Good call, dolj!). Below is the summary. I guess the next step is resolving P0AA6 issue. Time to do some more reading I guess.

    Any tips or suggestions will still be much appreciated!

    OBD-IIOBD-II
    DTCs: 4
    ----------------------------
    P0037 [0x0037]
    Heated oxygen sensor (HO2S) 2, bank 1, heater control - circuit low
    Oxygen Sensor Heater Circuit Low Input (Bank 1, Sensor 2)
    Status: Confirmed
    ----------------------------
    P0138 [0x0138]
    Heated oxygen sensor (HO2S) 2, bank 1 - high voltage
    Oxygen Sensor Bank 1 Sensor 2 High Voltage
    Status: Pending
    ----------------------------
    P1116 [0x1116]
    Engine Coolant sensor out of range/ECT Sensor Out Of Self Test Range
    Status: Pending
    ----------------------------
    P0AA6 [0x0AA6]
    Hybrid battery voltage system - isolation fault
    Status: Confirmed
    ============================
    Engine control unit #1Engine control unit #1
    DTCs: 1
    ----------------------------
    P0037 [0x0037]
    Heated oxygen sensor (HO2S) 2, bank 1, heater control - circuit low
    Oxygen Sensor Heater Circuit Low Input (Bank 1, Sensor 2)
    Status: Confirmed
    ============================
    Hybrid engine systemHybrid engine system
    DTCs: 1
    ----------------------------
    P0AA6 [0x0AA6]
    Hybrid battery voltage system - isolation fault
    Status: Confirmed
    ============================
    HV battery
    No DTC found.
     
    #13 Sean I., May 18, 2024
  14. Danno5060

    Danno5060 Member

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    I've enjoyed watching the guy from the South Main Auto YouTube channel. He seems to have a good explanation for diagnosing the O2 as well as other sensor problems throughout his videos. He shows how to track down and confirm what's going on, even though he's obviously tracked down the same problems with many other cars before.

    As to the P0AA6 Isolation fault, you're going to need to get the detail code.
     
    #14 Danno5060, May 19, 2024
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  15. mr_guy_mann

    mr_guy_mann Senior Member

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    You'll need the Autel AP200 to get the INF detail code.

    Clear codes, then ready up the car. The freezeframe data will show INF 526 (general isolation fault).

    The next time you try (and fail) to ready up, you'll be able to check again for a second INF code that should help narrow down the fault area.

    Posted via the PriusChat mobile app.
     
    #15 mr_guy_mann, May 19, 2024
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  16. Sean I.

    Sean I. Junior Member

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    I ordered the AP200 a couple days ago. It should arrive tomorrow.

    I decided to take out the HV battery and open it to see how it is. Below are some photos.

    ALL battery terminals were corroded, front and back. I took all the copper thingies and bolts are to clean them.

    I could put them back on the front side (the side facing head of vehicle) together just fine. But when I was putting them back on the back side, I keep getting sparks. The battery pack is on the ground on concrete floor. Did I do something wrong? Should I put it in the car in its original position to finish the job? How can I avoid the sparks?
     

    Attached Files:

    #16 Sean I., May 20, 2024
  17. mr_guy_mann

    mr_guy_mann Senior Member

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    Why did you take the pack out if you don't know what (specifically) the problem is? You need to put it back in before you can scan the car for the INF code.

    As far as "sparks", are you sure that you are putting the busbars (copper thingies) back in the correct positions? Did you take pictures of everything before disassembly? If you accidentally move one side of busbars over "1 stud", you end up trying to short two modules together instead of connecting them to the next module.

    Do you have a torque wrench to tighten the nuts to 48 INCH-pounds?

    Posted via the PriusChat mobile app.
     
    #17 mr_guy_mann, May 20, 2024
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  18. ChapmanF

    ChapmanF Senior Member

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    Also, a person following the Repair Manual instructions here would be making sure to use a socket wrapped in electrical tape (or dipped in Plasti Dip, etc.), to minimize chances of making sparks even with the busbars in the right places.

    The repeated sparks could be interpreted as a pointed question from the battery about whether the person doing the work has read up enough on how to do it safely yet.
     
    #18 ChapmanF, May 20, 2024
  19. Sean I.

    Sean I. Junior Member

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    So I did get Autel Maxi AP200 today.

    I put the battery back together and installed it to scan codes. AP200 threw more codes than Veepeak OBDII reader:

    C1241- 512 current: low battery positive voltage or abnormally high battery positive voltage
    C1242 current: open circuit in ig1/ig2 power source circuit

    B1650 history: occupant classification system malfunction
    B1660 history: p seat airbag active mode indicator
    B1801 history: open in d squib circuit

    C2122 current: cannot receive data from transmitter id2 (main)
    C2177 current: initialization uncompleting

    P0AA6 current -526 -613
    P0AA6 history

    B1421 current: solar sensor circuit (passenger side)



    I'm going to do research on all these codes. B1650, B1660 and B1801 are "history," do I need to be concerned about these?

    Is there a code that might be causing other codes? Which should I start first?

    Any input will be greatly appreciated!
     

    Attached Files:

    #19 Sean I., May 20, 2024
  20. TMR-JWAP

    TMR-JWAP Senior Member

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    The 613 code is the subcode you really don't want to see. That indicates the isolation fault is in the inverter output area or the transaxle itself. Complete opposite end of the car from the HV battery.

    But, the car self-troubleshooting isn't perfect. I just fixed a car last week that had the P0AA6/526/614 subcode, but the problem was tracked down to corrosion in the HV battery ecu socket. New sensor harness and replacement ecu and it was rock solid again. Maybe you'll get lucky also.
     
    #20 TMR-JWAP, May 20, 2024
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