Dash Warning lights - how to test?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by bharral, Aug 10, 2021.

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  1. bharral

    bharral New Member

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    Hello to All,

    First Post. I recently purchased a 2008 Prius base model. The car starts and drives fine. The 12v battery remains at 14v even with the headlights on. The Cruise Control engages and holds the set speed.

    Howver, the READY light has never illuminated, nor has the CRUISE indicator ever lit when the cruise control is engaged.

    The speedometer/odometer/trip and gear indications work fine - the board/display providing those functions was said to have been replaced previously.

    Turn signal, parking brake, and door open indications all work.

    So I appear to have some problem with at least some of the warning illuminators to the right of the speedometer module. I do see the Headlight indications, and I have a occasional MIL light which I have traced to a coolant control valve, which I intend to replace shortly.

    I think I recall reading that ALL warning lights are illuminated briefly during the transition to READY, but I do not observe that on this vehicle.

    Has anyone experienced these symptoms and resolved the issue?
    Is there any way to force illumination of all of the Warning indicators to verify the lamps/leds/etc. themselves?

    I am concerned that some critical warnings such as low oil pressure may not be functional.

    Blake in Arizona
     
  2. dolj

    dolj Senior Member

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    Put the car in IG-ON. All lamps on the combination meter illuminate with the exception of the master warning light (MWL) which is the big red triangle with the exclamation mark(!).

    The low (or actually no) pressure warning comes up on the MFD, and you don't want to be relying on that warning coming up to prompt you of low oil. Get in the habit of regularly checking the oil dipstick and top up as required.


    Prius power cycle modes:
    Mode
    Action​
    1 ACC
    • With the car in OFF; and the foot OFF the brake; press the start button once.
    2 IG-ON
    • If the car is in OFF; with the foot OFF the brake; press the start button twice.
    • If the car is in ACC mode; with the foot still OFF the brake; press the start button once more.
    3 READY
    • With foot ON the brake; press the START button once; this can be done when the car is in any other mode.
    4 OFF
    • If the car is in READY; press the START button once; it does not matter whether the foot is on or off the brake.
    • If the car is in ACC mode; with the foot OFF the brake; press the start button twice.
    • If the car is in IG-ON mode; with the foot OFF the brake; press the start button once.
     
    #2 dolj, Aug 11, 2021
    Last edited: Aug 11, 2021
  3. ChapmanF

    ChapmanF Senior Member

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    I think if you use Techstream, choosing Combination Meter from the system select screen and then Active Tests, you can turn individual warnings on and off.

    Like the power-on test, this mostly tests the meter and warning lights themselves. If you're concerned about the external circuits that trigger them, there can be other checks you could do to learn more.

    The oil pressure warning circuit is pretty simple, because when you're just ON and the engine isn't running, there is no oil pressure, so the warning should light up; they don't need any special test provision to make it light for the self test. (What they do need is a special gate to suppress it when your car is in READY and the engine happens to be off!)

    If the oil light is on when you are in ON mode, but it goes out if you unplug the oil pressure sensor under the hood, then you've confirmed that circuit end to end.
     
  4. bharral

    bharral New Member

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    Good Morning to All,

    Thanks for the replies. None of my warnings illuminate in IG-ON. I am told the Combination Meter has been replaced on this vehicle. That makes me wonder if perhaps a connection to Warning Panel was disturbed during that process. I can see the headlight and MIL indications (although not at when transitioning to IGN ON), so the panel has at least some function.

    I will try to acquire Techstream/cable. Seems to be several options - if there is any updated HW/SW to simplify installation on Windows 10, I would appreciate a pointer. I do have some old Win7/8 computers that I can use if necessary.

    I suspect the Determination/Detection circuits are working - If the Prius was not actually in READY, I'm sure it would not start - All posts I have searched for no READY indication state the the vehicle will not start. So my current theory is a bad warning board and/or faulty connections to this board (I am assuming it is a circuit board, but I don't know).

    I watched several videos of Combination Meter Replacement, hoping to get a glimpse of the Warning indicator board, which is just to the right of the CM and closer to the driver. However, I was not able to get a good look. I also searched Toyota parts diagrams to find same, but was unsuccessful. Any pointers to that information or P/Ns would also be appreciated.

    I understand the cautions about Oil Pressure. I checked the Oil level in the car at purchase - It is clean and full. I do not rely solely on warning lights to make sure a car is healthy.

    The car is drivable as is, but everything else on the car is working, and these issues will continue to bug me until resolved.

    Thanks again,
    Blake in Arizona
     
  5. dolj

    dolj Senior Member

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    Two things. 1) if you want to install it on Win10 make sure you get a cable that explicitly says it has a 64-bit driver. 2) If the Win10 device is your main computer I would strongly suggest that you install Techstream in a VM.
    There is a good thread pinned to the top of this forum called 'Combination meter repair - DIY'. This contains some good pics and info. Have a read of that and see if that helps.
     
  6. sam spade 2

    sam spade 2 Senior Member

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    Others are helping with your main problem.......so I will offer just a bit of clarification that might be helpful in the future.

    That voltage is NOT the battery voltage but is the CHARGING voltage while the car is running (READY).
    To measure the actual battery voltage, everything must be OFF.
     
  7. bharral

    bharral New Member

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    Thanks for the reminder about 12v battery check. With everything off it shows 12.6, drops to 12.2 with headlights on. I think that should be good enough?

    I read the entire thread on the CM, but still don’t understand if it drives the warning/info lights to the right of the fuel gauge (ABS,VSC, etc.), and if there is a separate electrical connection that drives these. I would like to have a better idea before tearing apart the dash (the CM thread does have pretty good info on how to do that.

    Thanks to all,
    Blake in AZ
     
  8. bharral

    bharral New Member

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    Adding more information discovered at another Prius sight.

    The warning light panels to the left and right of the combination meter appear to be driven by the combination meter itself. Reviewing the CM thread here, these ribbon cables are clearly shown (and in fact detached/reattached during CM repair). So it now appears obvious in retrospect that the ribbon cables attach the CM to the back of the Warning modules, which contain LEDs. Since LEDs are quite reliable, I suspect a bad ribbon cable or cable connection. Another possibility might be a bad CM itself, but all the indications on the CM Itself are fine, so I’m thinking CM is OK.

    Maybe the CM repairman just failed to seat the ribbon cable properly…

    I think I have enough info to justify tearing apart the dash when I get the time to do so.

    Thanks for all the help.

    Blake in AZ
     
  9. sam spade 2

    sam spade 2 Senior Member

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    Yes should be.
     
  10. mr_guy_mann

    mr_guy_mann Senior Member

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    Or the CM repair wasn't done properly and it's still faulty.

    Posted via the PriusChat mobile app.
     
  11. mr_guy_mann

    mr_guy_mann Senior Member

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    On a Gen2, the CM has no self diagnostic capabilities via the OBD port or a scantool, at least Techstream doesn't show the CM at all.

    Does the Prius even have a dedicated oil pressure warning dash light? I read somewhere on the forum that it has a warning message that pops up on the MFD- but that never shows as part of any "bulb test". If you go into engine data on Techstream, you can monitor engine oil pressure switch status- "on" (low or no pressure, ie the warning "light" should turn on), or "off" (some pressure).

    Posted via the PriusChat mobile app.
     
    #11 mr_guy_mann, Aug 14, 2021
    Last edited: Aug 14, 2021
  12. RRxing

    RRxing Senior Member

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  13. ChapmanF

    ChapmanF Senior Member

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    Well, not so much a message. It looks just like the usual oil-can icon for a warning light, but it's just an icon that gets drawn on the MFD.
     
  14. sam spade 2

    sam spade 2 Senior Member

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    That procedure does not specify if you should leave the lights ON or turn them back OFF before taking that measurement.
    The values given will likely NOT be seen if the lights are still ON.......unless maybe you have a brand new fully charged battery.
     
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