T-SB-0172-09 Combination Meter - Intermittent Display

Friend of me has this problem on her 2005 or 2006, I forget. So, I bought a failing combination meter on Ebay cheap and looked at the circuit around the TLE4278 LDO and watchdog for the Fujitsu processor. I was able to easily reproduce the problem by powering the combination meter from a 12V supply (GND pin 14 and +12V pin 21). If I interrupted the power supply for a short moment (slightly less than 1 sec) then the Fujitsu processor did not boot up quickly enough to reset the watchdog in time, so the board got into a funk of trying to reboot several times per second repeatedly until you either interrupted the power supply again to stop the watchdog longer on power-on and allowing the Fujitsu to start properly resetting the watchdog, or I could also get the board out of the funk by touching the Gate of the 12V power switching FET1 (marking J377) which is controlled by transistor TR3 which receives its control from the Fujitsu. Weird that, since the Gate is controlled by relatively low resistors R4 (15k) and R3 (10k to +12V).
Anyway, the time-delay for the Watchdog is controlled by the capacitor C5 which is likely the minimum 47nF as suggested in the datasheet, which gives a watchdog trigger time of between 35 to 61ms. To check if my theory of speed of startup of the Fujitsu is correct, I added a 100nF capacitor in parallel to C5 (from TLE4278 pin 6 to ground) and after that I could not reproduce bringing the board in the "Funk" state where it repeatedly rebooted, apparently the Fujitsu is now fast enough to boot before the watchdog bites.
NOTE: this experience suggests that the 12V ignition power to the Combination Meter has a short interruption while starting the car, this will allow the watchdog to reset the Fujitsu (due to undervoltage) but keep the watchdog circuit alive enough to immediately start biting as soon as the power returns, preventing the Fujitsu from starting fast enough to start triggering the watchdog.
It seems that a simple and cheap 100nF cap soldered parallel to C5 and increasing the trigger timing likely be a factor 3 will take care of this problem and make the Combination Meter work normal again.
Tomorrow I will install this modified Combination Meter and we will see how it behaves in daily operation!

 

Patrick, I added the picture to the original post, as to have everything in one place. You see the blue 104 (=100,000pF = 100nF) capacitor soldered from C5 to ground.

 

Awesome work. I haven't experienced this problem yet but this is very good of you to share with others because the time limit has now run out on the Toyota customer service campaign for this issue.

 

Here is another picture of a second Combination Meter that I fixed. It used to fail about once every 5th time starting and after adding the 100nF capacitor next to IC1, from C5 to ground, I powered it up (from a 12V supply) and after about 100 times powering up correctly I installed it back into the car and asked my friend to let me know if it ever fails again!

 

Exactly - that is my main reason to dig in and share, I recognised that people (like my friend) are beyond the warranty for the Combination Meter, so now they need another solution, preferably available from a local repair shop.
BTW, I took about an hour and a half to take the dash apart, remove the Meter from the dash, fix it and put everything back together after watching the following Youtube video (it was my first time taking the dash apart (!):

 

It appears that the simple fix (add a larger time constant capacitor on the watchdog) is not a perfect solution, or the value may not be perfect yet, as I got report that the 2005 of my friend needed one more reset since installing the fixed unit. But normally the car would need to be reset every other time it was turned on, so she is now avoiding the hassle of two dozen resets (unplugging the 12V battery) between the occasional recurrence of the failure to start up.

 

Hi EV_Cor, you might want to peruse this thread: combination meter repair - DIY and maybe move your discussion there. That thread has all the information you should need to make a lasting repair.

Post #71 (on page 4) has a nice summary of what needs to be done.

hope this helps.

 

Interesting! Though I don't agree with a couple things said there
and I have an idea of my own that would better explain what is under the black goop that is potted on the repaired boards.
Here is the text of an email that I just sent to discuss with one of the other Prius Technical Stuff members:

I read from others that it makes sense to replace the 3 electrolytic caps around
the 5V regulator. Personally I am not convinced that it makes any difference with the
exception of the output cap on the 5V line C3 (100uF 16V), since that is the only one spec'ed in the
datasheet to require to have ESR below 5 Ohms (and I heard it must also be *higher* than a minimum, probably 1 Ohm)

The first thing that I am going to try however is to add a ceramic cap to the *input*
of the 5V regulator, since the datasheet is pretty clear that there should be a 470nF
cap across the chip's power input while I can't find anything directly attached to pin 13
other than 2 vias to a trace on the back, which connect to another 2 vias which connect to the
large electrolytic cap C2 and curiously to the series-connection of C4 and C67.
I do not understand why anybody thought that instead of a ceramic cap immediately between
pins 13 and 12 it would be better to have a length of trace, double set of vias and then
double the impedance by having two caps in series. Weird stuff, right there.

So, I am going to remove by parallel cap on C5 to make it fail 1 in 5 times again,
then add the ceramic cap on the input and check if that makes a difference in
how often it fails, if it still does then swap the output cap for a low ESR one
and verify once more. After that I might still put the parallel cap on C5 back
just in case, but I strongly suspect that input and output caps are what makes
this regulator an oscillator and causes the meter to fail... To Be Continued

 

OK, in order to find out what has the most impact on the operation of the 5V regulator IC1 (TLE4278) and to verify my suspicion of the input capacitance having influence, I removed my fix of the 100nF cap parallel to C5 and verified that the Combination Meter again failed approx every 5 times power-up, which it did.
I then added a ceramic capacitor from pin 13 to ground which had no effect, it was still failing to start up approx every 5 times. So then I added a low ESR cap on the 5V output, pin 9 to ground in parallel to C3. After that I could not make the meter fail again, so I suspect that indeed the 100uF 16V capacitor on the 5V output is marginal and allows the regulator to oscillate too much, causing theprocessor to fail to start up properly and since the processor boot-up is not fast enough to trigger the watchdog in time (C5 is too small) a failure during boot-up is a permanent failure until power down. The increase of C5 should allow the processor to boot up unless the oscillation of the regulator affects the processor too much. That may be why simply increasing the value of C5 works most of the time but not always, so I recommend replacing C3 with a low ESR capacitor, the other thread suggested this one: http://www.mouser.com/ProductDetail/Nichicon/UUD1C221MCL1GS/
as well as adding 100nF parallel to C5.

I also think that I found what pEEF hinted at for the electro-mechanical problems in the board. This does not affect the startup of the meter and the car will continue to work normally, but the display itself may become intermittent due to the transistor TR10 that is bolted to a small heatsink, which is held to the board with a screw that also attaches a plastic shroud and thus there is mechanical stress on its legs and eventually it will try to pull its legs out of the solder pads. I tried to take a picture of the cracks developing around its legs but had a hard time to try and capture it, so in the end I simply re-soldered the pins to make sure they are well attached to the board.
Below some pics that go with the text: (NOTE that the last pic still shows the ceramic cap on the 12V input which is not needed, besides the black SMD Polymer capacitor on the 5V output)

 

I have a few questions for all you Combination Meter gurus here on PC:

• Does my (2008) Prius count miles while my dash is blacked out?

• My dash has barely been on for the past year or more and I suspect it hasn't counted all the miles I have driven, but I could just be wrong and terrible at tracking my mileage.

​

• When my dash is blacked out from a failed combo meter boot, are all of the braking systems operating normally or does the car revert to a 'safe' mode or conservative generic control scheme?

• Also, does anybody in California know if my car will fail smog inspection if my combo meter happens to not turn on when they check out my car as long as my check engine light is off and my ecu's all read out passing results?

• I know the failed combo meter sets DTC B1271 in Gateway ECU, but I don't think that code causes CEL to illuminate, does it?

​

 

Regarding your last question, I don't know for sure but I have a couple of coworkers that are smog techs. I can ask about this next Tuesday when we are back at work.

I did ask some people about whether any code would cause you to fail (because I also own a Jeep that has some electrical issues) and the consensus was that only codes that light the CEL would cause you to fail smog.

I can see one additional problem; I don't know if they can pass you if they can't verify the mileage. I will ask about that as well.

 

Maleko,
When the combination meter is blacked out there are no miles being added to the odometer. Expect that any Prius that has spent much time with a bad meter will not have a 100% accurate odometer.

If your car is an 08' and you've been having this problem for a year why haven't you had it fixed for free by Toyota? The early 08's are starting to go out of warranty by now but anytime last year you should have been good to go.

Matt

 

Regarding California smog check- the tech does not need to be able to read the mileage for the vehicle to pass, but must verify that the CEL lights up when in Ig-on ( key on not running for non hybrid) and that the CEL goes off when Ready (engine running for non hybrid)

 

The "short" answer is because I got a little screwed and confused when my local Toyota dealer basically didn't want to deal with me and told me a ridiculous set of requirements in order to get combo meter addressed "for free".

Bottom line there, was after a single interaction with their service department I decided I trusted them 0% not to screw me with unnecessary work trying to be passed off as the cause of my problem which I was knowledgeable of at the time and that it was a common issue with 2G but they did not care.

Ive been my own mechanic since I can remember and was raised on computers so I'm a bit skeptical, especially after having worked for Ford in a lube house briefly.

Also, raising a first toddler and only having one family car to get us through 1000 miles/week commuting makes it tough to give up your wheels and count on somebody else not to take advantage of you just because of proprietary computer BS and requirements put in place by Toyota / dealers.

They wanted $100 or more just to read codes which I refused to pay regardless of the issues that popped up. Also at this time I was aware of Techstream but just hadn't gotten around to purchasing the hardware and setting it up yet.

Fast forward until recently when I got a P0420 code right before our first ever required smog on the car. That prompted me to get Techstream setup and become familiar with it. Then I got on the horn to find a more reputable dealer or garage in the Bay Area to do the work (since our car had less than 150,000 miles on it) .

Found the dealer, coaxed a free cat out of them, had a great (night and day) experience with them and they took care of me even if a bit begrudgingly. Unfortunately by this time it was sadly too late for our meter to be replaced for free. They wanted $700 or some .

I would rather just buy one online preprogrammed to my mileage and change it myself. The cost of living out here is ridiculous and we survive on a single income so I've got to be crafty where I can. All said, I think we still got the better end of the deal for being patient.

Also, called Toyota corporate to see what they could make happen. I emphasized my night and day experience between two of their neighboring dealers and they offered me ~$450 credit for service through them any time in the future- parts or service. It's a shame it had to come to all of this and take this much time for everybody, but like I said, I feel like Toyota corporate did their part to help me out and correct their dealership's reputation.

Posted via the PriusChat mobile app.

 

I see that you can repair a touch screen. I have an 08 and it won't respond to touch. All of the other functions work just no response to touch. Please advise and thank you for the assistance.

 

So the dealer is charging me about $550 for parts and labor and is strangely mandating that my car stays in the shop, while the part is being shipped "so that the odometer record stays accurate". While I don't care to drive a car without a dashboard and have accepted a Gen4 Prius for $35/day, I think this policy is completely crazy because they can read the odometer from the OBDII port when I bring it in for the exchange. Supposedly this installation "can only occur at a dealer" and "the part isn't available independently".

Anyone heard of this before?

 

Good price for a dealer.

There are two things which make this policy not crazy.

1. While the CM is black, no milage is accumulated, so reading the ODBII will not show the increase in milage. Further;
2. When the new CM is ordered, the current milage is sent so that it can be programmed into the new CM. Therefore, any further miles added between ordering and installation will not be reflected. The programming of the CM is done at the factory, not the service center. This effectively puts the car off the road while the repair is done.

This is correct, Toyota is the only source of a new CM. Any CMs out in the wild that are sold are used and are harvested, either, from wrecks, or by way of an exchange programme with those that do repairs. You also can send your own CM for repair to these 3rd party repairers, which would involve DIY removal and reinstall.

hope this helps.

 

Thanks for explaining this, is there a law about this or is it Toyota USA, or individual dealer policy?

 

There's no law that states you must have a part replaced at the dealership. What they probably meant was that the only source for a new meter is thru Toyota and that is true. You should be able to buy the part and put it in yourself. If your dealership doesn't want to sell you a combination meter there are several dealers who sell parts online that would be happy to do business with you. As I recall the new meters are around $400 so the price they quoted you isn't bad as long as it includes labor.

We sell rebuilt meters programmed and ready to install for $150 and most owners do their own installs.

Matt