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07 won't start and can't read codes

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Larry Kosher, Mar 19, 2022.

  1. Larry Kosher

    Larry Kosher New Member

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    Hello, PriusChat.
    I just got this car and was never able to start it yet.
    • The 12-volt battery is fully charged.
    • No burned fuses.
    • I tried 2 different scanners - the cheapest Bluetooth adapter and $200 Innova - neither read trouble codes, while all the lights on the dash are on.
    • While a scanner is connected I can clear the error codes and the red triangle of death disappears for a second and quickly reappears
    • Overhaul it looks like a burned ECU.
    • It behaves as if it was started in accessory mode (as if the brake pedal wasn't pressed)
    • At the same time, it reacts on the brake pedal - lightens the stoplights, and even produces noises with the auxiliary pump.
    Any advice, please? How do I diagnose it?
     

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    #1 Larry Kosher, Mar 19, 2022
  2. ChapmanF

    ChapmanF Senior Member

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    While trying to get access to a scan tool that can show you your trouble codes, you can get at least some of them using the Tc to CG jumper, count warning light blinks method (you can search up many other threads with those details). That method works even when you haven't got a functioning scan tool handy.

    The codes behind the big triangle light regrettably don't have blink code versions, so those will have to wait for getting access to a scan tool that can read them. But you can at least get a head start on troubleshooting by getting the codes now from those ECUs in the car that know how to do blink codes.
     
    #2 ChapmanF, Mar 20, 2022
  3. PriusCamper

    PriusCamper Senior Member

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    It's a bit odd that you can briefly clear the codes but you can't see the codes before they're cleared?

    What OBD software are you using? Have you tried to read codes on a device that's compatible with Prius subcodes? Like Dr. Prius app?

    First step is to confirm you're using a functional OBD2 adapter... Majority of them on the market are garbage. Here's a buyer's guide: Hybrid battery diagnostic and repair tool for Toyota and Lexus
     
    #3 PriusCamper, Mar 20, 2022
  4. ChapmanF

    ChapmanF Senior Member

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    The message sent over CAN to clear codes is a standard message. A tool can send it without querying for codes first or without knowing much about the codes that are present. I think there are even some OBD-II gizmos for sale that have only a 'clear' function, and can't query for codes at all.

    It's a weird thing to do, but nothing in the system prevents it.
     
    #4 ChapmanF, Mar 20, 2022
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  5. Larry Kosher

    Larry Kosher New Member

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    Thanks, everyone for the answers. While people discuss here OBD scanners, I would like to clarify that my problem is not a faulty tool. The car actually shouldn't output codes over OBD and this is why. At the current stage of the investigation, I can confirm that the car always starts into accessory mode, as if the brake pedal was never pressed. I tried it on my other (working) Prius and if you start it with no foot on the brake pedal the dash looks the same, the LED on the start button stays orange and the OBD also reports no codes. The only difference is that it doesn't have the red triangle of death on.
    So far I did the following:
    1. replaced the stop switch - i.e. the one on the brake pedal; the car's original one was fine also
    2. replaced the IG1 relay (no problem there also) and I can sense it's clicking when I press the start button
    3. tried hooking up another ECU - that didn't change anything.
    4. there's not a single fuse out on it; not that I know of.
    The attached photos show the car dash with the lights on, the start button after I tried to start the vehicle, and also how I tried to start it with other ECUs. Is it a faulty hybrid ECU? I mean, the one inside of the battery? My current theory is that it might be a faulty connection between the IG1 relay and the ECU. Any advice is much appreciated!
     

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    #5 Larry Kosher, Mar 20, 2022
  6. Larry Kosher

    Larry Kosher New Member

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    Okay, it is not the power control module (the backbox under the box): I replaced it, that didn't help. How do I decode the TG - CG codes? I got 31 on the ABS light.
     

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    #6 Larry Kosher, Mar 21, 2022
  7. Larry Kosher

    Larry Kosher New Member

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    I solved the issue. That was the spoiler, now is the explanation.
    While searching on this site I've seen so many times when subjects like this were left abandoned, i.e. never resolved. For the sake of integrity and to give back to this helpful community (and to the potential future googlers) I'm writing this conclusion post. To begin with, a quick summary of symptoms again:
    • I just got this car *as is*, I never had it running
    • The car never displays "ready" on the instrument cluster, hence it doesn't (didn't) go into R or D
    • The LED on the START button stays orange
    • The dashboard emits a lot of light (all the warning lights are on)
    • Couldn't read the error codes - all tested scanners reported "no errors stored in the ECU"
    To my inexperienced eye, it looked like a power failure, hence I was investigating the ignition diagram and tried to follow it IRL, checking the corresponding fuses, replacing relays (I got all possible relays for gen2 Prius of a junkyard), testing connectivity, etc. Unable to detect a problem, I started to swap modules from another (working) car - I did so with ECUs, the power control module, and the brake module (the black-box next to the 12 volts battery) - nothing changed. My last idea was to swap the hybrid battery altogether, suspecting that the control unit of it might be faulty. While unhooking the safety switch of a working car battery I noticed how the switch is supposed to be properly engaged. That was the light bulb moment! I run to the faulty car, checked the switch, and there it was - while the switch was engaged (the handle of it was in an upright position) it wasn't inserted down. Therefore, there was no contact and the hybrid battery wasn't engaged! Turned it on properly and the car started immediately.
    Whatever the issue was with this car (most probably a faulty ignition relay IG1), I must have solved it in the process of this rather long and extensive diagnosis. Anyway, happy to have it running! Thanks, everyone for the input. Appreciate that!
    P.S. The attached photo shows the culprit of the startup failure.
     

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    #7 Larry Kosher, Mar 22, 2022
  8. ChapmanF

    ChapmanF Senior Member

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    The car has four distinct modes, named OFF, ACC(essory), ON, and READY.

    READY is where you normally end up after pressing the button with the brake applied. There is a green word READY on the dash and you can drive the car.

    ACCessory is where you get by pressing the power button one time without the brake. You don't get dash warnings or gauges, but you can play the radio.

    ON is where you get by pressing the power button two times without the brake. You have gauges and warning lights, but no READY indicator, and the car won't drive.

    The state you end up in if you try to go READY but the car's checks don't pass is ON. Your photo shows dash warning lights and the gauge cluster, which is what ON looks like.

    Diagnostic codes are reported in ON mode or in READY mode. (The repair manual also contains a procedure involving a certain dance with the door courtesy switch, to wake up the ECUs to report trouble codes if ON or READY can't be reached.)

    That's one of the most often reported experiences on PriusChat. In case you ever face a similar situation and have a chance to read the trouble codes, that situation is reported with code P0A0D.
     
    #8 ChapmanF, Mar 22, 2022
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