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I have a 2006 Prius and the dash lights keep going out! I know how to get them to go back on by resetting the 12v battery but the problem is becoming more frequent! Why are the dash lights going out in the first place?
 

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I have a 2006 Prius and the dash lights keep going out! I know how to get them to go back on by resetting the 12v battery but the problem is becoming more frequent! Why are the dash lights going out in the first place?
Alan it happened to me first time on my '06 yesterday. And it wouldnt shut off unless I held the start button several seconds, then the charge computer and the radio stayed on until I removed the key fob. So no speedometer or gas gauge w/ lights out. How did you reset the 12v?
 

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Alan it happened to me first time on my '06 yesterday. And it wouldnt shut off unless I held the start button several seconds, then the charge computer and the radio stayed on until I removed the key fob. So no speedometer or gas gauge w/ lights out. How did you reset the 12v?
...and this am all is normal.
 

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...and this am all is normal.

This is my first post, just joined.
Hi Everyone!

I am quite familiar with this particular phenomenon, so i figured i would use this opportunity to chime in. i had a 2006 that had this exact problem where the dash, also known as the Combination Meter or Dash Cluster would, depending on its mood, decide if it wanted to work that day or not. sometimes cycling the power button would coax the dash to come back to life, but as time went by, the issue got worse and worse.

Turning off the car when the dash isn't working was an equally frustrating trial and error experience as trying to convince everything to turn on and behave. Eventually i figured out that, to turn the car OFF, you would have to hold the brake pedal down, and then press and hold the Power Button, that forces the car to go straight into Accessory Mode. Then let go of the brake pedal and Power Button, and press the Power Button twice, not too fast, not too slow, and it should shut off the car completely. if the MFD display is still on, the car is still on (in Accessory Mode), and you'll need to try again to turn it off.

This problem is a relatively common issue with the 2nd Gen Prius dash, and there was even a Recall on the dash cluster, but most of us never heard about it until the Recall expired, and in my case, the Dealership was relatively useless and clueless to help, until it was too late to make a claim.

Back to the problem at hand:
There are actually two possible issues that can cause the dash to "ghost" as i call it, and go blank, leaving you with an otherwise functional car but sans speedometer, gas gauge, cruise control, backup camera, and sometimes a few other features, that could eventually strand you or get you into trouble if you accidentally run out of gas or drive too fast and garner unwanted attention from the men in blue with shiny badges.

The first thing to check is your rear 12v start battery, located on the right side rear corner of the car under the cargo area. if the start battery (which is responsible for firing the electronics to "start" the car, and allow the main traction HV battery to take over) is too low, it has been reported that it can prevent the proper initializing of the dash. even if the car otherwise has always started up every time, it may be tired and low of charge and nearing the end of its life, and this is just an early symptom of imminent failure. some of the more complicated electronic boards tend to be temperamental and finicky and want full voltage and amps to turn on successfully every time. so getting the battery tested is easy, relatively simple and quick, to determine if this is possibly the culprit. i would disconnect the battery to get a more accurate read of the voltage and amps it is putting out.

The second possibility is by far less pleasant. the circuit board that is the Combination Meter is failing. give it time, it will eventually completely fail and the ratio of how often it works vs how often it stays off when you start the car will gradually and frustratingly go up until almost every time it will remain blank when you start the car. Toyota put several larger capacitors on the board, rather than opting for more reliable micro capacitors running lower power requirements, to save a few cents in production cost. over time and thru normal operation, these more power hungry capacitors wear out and fail, causing intermittent failure of the board function, preventing the display from working, and keeping you in the literal dark. this is a known issue with computer motherboards and flat panel televisions, the capacitors (aka caps) sometimes will visibly show failure and their otherwise flat silvery metal tops will bubble or swell subtly and become dome-like to the touch.

Unfortunately, tho the repair is relatively simple if you can solder electronic boards, and capacitors only cost a few dollars each, it is not a small task to dismantle the entire dashboard to get to the dash cluster. if you look online, you should be able to find a multitude of videos that have a walk-thru of how to remove and reinstall the dash cluster.

If you search around, you should also be able to find an online trusted merchant who specializes in repairing or replacing the cluster. Note, that often they will ask you to send in your part and they will send out a previously repaired unit (not a brand new part), and they will ask you some questions, including what your mileage currently is, so that the replacement module can be properly programmed to match the accurate odometer reading of your vehicle. it's important to be completely honest and accurate, and leave nothing to chance. i recommend taking pictures of when the dash is on for your records of odometer readings, prior to removal of the old dash cluster and prior to ordering a replacement module, justin case anyone questions the repair or odometer reading, any time in the future.

2004-2005 are one configuration of dash display, and 2006-2009 are a slightly different updated dash display. the only real difference is that the gear position info and the fuel info position are swapped, otherwise the part is completely interchangeable, but some people might get annoyed if they choose the opposite one and suddenly the gauge info feels wrong and backwards to what they are used to seeing.

The last time i checked, a few months ago, the new dash display part can be had for under $200 total, just don't expect a brand new part installed at the dealership, they'll quote you easily a $1200 bill for that repair. if you are automotive mechanically handy, comfortable with working on electronics and have the time and courage, you might be able to do the part swap yourself in a weekend. it is a daunting task tho, and even an experienced guy who has done it before might take the better part of a day. and many things can go wrong or not work after it is all reassembled, requiring that it all be taken back apart again to see what step or wire was missed, so i would recommend finding someone who knows what they are doing that can perform the task correctly and in a timely manner.

If you can live with the dash out issue, there is no harm to other parts of the Prius. Toyota designed everything to work discretely, you just won't have certain functions and reported info available to you. But the problem will only get worse, not better. and running out of gas can do harm to the car, to say nothing of the inconvenience of getting stranded until you get gas. so i recommend looking into addressing the problem sooner rather than later. not having a gas gauge is a guaranteed way to run out of gas, i know from personal experience.

Oh, just to share the knowledge, if you ever do run out of gas on a 2nd Gen Prius, and you turn it off, you need to add at least 5 gallons to the tank before attempting to start the car.

And Very Importantly: you only have 3 chances to successfully start the vehicle before it goes into lockdown and will not start even with a full tank of gas.

If the car is attempted to be started with insufficient amount of gas to trigger the gauge to change from zero for the car to realize that you added fuel and it is ok to try to start the fuel pump, minimum >3 gallons, 5 to be on the safe side... the car won't tell the fuel pump to operate and the car won't start. fail 3 times and you have one of two recourses: either disconnect the 12v start battery, let the car sit for a day or two until the computer clears that hidden safety code protecting the fuel pump from damage trying to dry start repeatedly, or have it towed to a Toyota dealership who will happily clear the code and charge you for the service, on top of the tow bill you just incurred.

So plan accordingly, and choose wisely if you want to risk that scenario. your Prius can drive on pure battery power after running out of gas and screaming at the driver with a scary triangle of death on the MFD, for maybe two or 3 miles max, assuming the battery was mostly full when the gas tank depleted, and depending on your speed, hill terrain, driving style, if you don't turn off radio and a/c and slow down etc, and how much of a lead foot you are. so don't bank on limping far on electrics only.

and BTW, running the main HV battery down to near zero is a very VERY bad idea, it will stress and damage it, and severely shorten its life. and replacing the traction battery is quite an expensive endeavor. the main traction battery is not designed for such deep cycling the way a 3rd Gen PiP (Plug-in Prius) is, that can drive 10 to 20 miles in EV mode. the 2nd Gen Prius is an amazing hybrid, so know its capabilities, treat it right, and it will last a very long time.

Hopefully your issue is just the 12v battery, i was not so lucky. if you have any questions, i can do my best to answer them :)
 
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