combination meter repair - DIY

I would imagine that the handshake would still be an issue if I extract the PCB and just replace it? How are people able to order replacement PCBs and get it to work if that is the case?

 

I don't know the details, but since we know they must program in the odometer reading my best guess is that they also program in the VIN, or some cryptographic hash of it. There is also the possibility that there is no such VIN checking and something is wrong with the (re)installation, like a loose or omitted cable connection, or the replacement combination meter might be defective.

 

I had this problem with my 2008 Prius in February, this year. So, I replaced all three capacitors. The problem went away. Now, it has returned. Could it be the same three capacitors again, or something else? How would I diagnose the issue?

 

It could be the replacement capacitors, especially if you used old capacitors (long past manufacturing date, or recycled from another device ) or piggy backed them on the originals and left those in. To show definitively that the capacitors are bad you would need test equipment to measure the capacitance and the ESR. Bet you don't have either - I don't. You would probably have to take at least one pin out of the board to test them, and at that point, you might as well just put new ones in, as even top of the line ones are not expensive at that size. There is a remote chance that the capacitors might have bulged or burst, but having that happen in under a year would be really, really, really unusual, even for a really poorly made capacitor.

I would also suggest carefully inspecting the board near where the work was done to make sure there isn't a stray blob of solder, a pad lifting up, a scorched component from an errant soldering iron touch, or that sort of thing.

 

OK, thanks. I have the replacement capacitors in hand. I also got the voltage regulator. Just need to set aside a day to do this.

I was wondering if a low 12V battery could also cause this issue? When I tested it, it was a bit low. 11.8V. It dropped to 11.1V when the headlights were turned on. Then, with the engine running, 13.8V. Since it is due for replacement, maybe I just do it, and see if the speedometer display issue improves.

 

This was measured at the battery or the jump post with a voltmeter? 11.8 V is pretty low for this battery type. They seem to lose capacity easily when discharged that far. Oddly though, 13.8V when the motor is on indicates a not so bad battery. The 12V in my car has maybe 7Ah capacity, and when the car is running it reads 14.10 V once it settles down. (It starts at 14.5 or 14.4 then drops to 14.3 then 14.2 then finally to 14.1 over 10 seconds or so. The higher that voltage the worse the 12V, so by that metric, your battery is in better shape than mine. I recently had a chance to measure battery voltage on my car when it was sitting unlocked and unused (other than the back doors opening a couple of times each day, left the hood unlatched the whole time) and it was losing about .05V per day. It would probably lose more if it was locked, as the built in alarm system would then also be active.

I'm trying to think of why the battery would matter for the display once the car is going. The combination meter will be seeing that 13.8V, which should be plenty. The only thing I can think of would be the combination meter electronics going into a funny state when the 12V is low when the car first turns on and never coming out of it. Possible, but seems unlikely.

If you have access to a battery charger it would be a good idea to charge this one up. If you want the car to do it it might take hours to get to a full charge. Easier to let it charge overnight, assuming you have the equipment and a place to do this.

 

I measured the voltage using the built-in check, via the combination display. Is it not accurate?

I do have a battery charger. How do I charge the battery? Via the jump start terminal under the hood?

 

No, if anything it helps to hide the issue.

I don't know why exactly, but observations by many people over several years demonstrate the higher voltage of a new battery exacerbates the CM start-up failure.

 

OK, thanks. Interesting thing this morning. So, the combo meter was blank this morning, as it has been consistently whenever it gets cold. I immediately turned off the car and connected a battery charger to the jump start connector. The combo meter was illuminated when I started the car again. Perhaps it would have been the same if I hadn't connected the charger. No way to know. I'll keep running this experiment every morning. If it repeats, then it may just be a low 12V battery.

 

In theory either at the jump start or on the terminals at the battery. In practice the Battery Tender Jr. and Harbor Freight 4A battery charger (63350) I own both give up far too early at the jump point on my 2007. I have no idea why. So I use them directly on the battery terminals, usually with the wires that plug in at the gizmo on the positive post disconnected. Then they both work like they should.

Note, with these chargers and probably many others it is essential that the surface charge be removed before starting to charge or they misinterpret the high voltage as the battery being more charged than it actually is. In some cases they will go straight to "maintenance mode" without doing any real battery charging. If charging is interrupted for any reason the surface charge has to be removed again.

 

This morning, I connected the battery charger and started the car. Dark combo meter. So, battery level doesn't appears to be the root cause. It does seem to contribute somewhat in that the combo meter came on after a couple of tries. Without the battery charger, it would have stayed dark until it's fully warmed up, like in 10 minutes of driving.