Remote Key Issue

I'd try replacing the battery in both keys first. It's a cheap diagnostic.

 

Sorry to revive an old thread, but I'm having the same problem as the original poster with my 2013 Prius C 2. I replaced the battery in my key, but it still won't lock/unlock. Anyone have any ideas?

 

Hello Brady B, Portax,
Did you manage to resolve the issue?

It looks like I'm the third one with exactly the same problem.

Based on the description, I recently got exactly the same problem with 2014 Prius C One. I have 2 regular metal keys (not smart ones) with remote door opening function. The symptoms are the following.

1) Have 2 keys with remote open/close buttons. One stopped working at once. The other gets gradually worse with time.
2) Spare key (usually not used) stopped working completely.
3) The key car usually is driven with works intermittently. Sometimes doesn't work at all for days.
4) Found a sequence of actions needed to make it work for some time. If the car is unlocked and left with a door opened for ~10mins or driven for some time then locked and left alone, the key starts working ~ 30mins to a couple hours later. And keeps working for a few hours. The next morning it usually doesn't work and the procedure needs to be repeated.
5) Aux battery voltage 12.6V.
6) Totally dead key battery voltage 3.3V.
7) Intermittently working key voltage 3.045V.
8) TPMS system (which I believe is also used for remote door opening) seems to be at least partially functional at least at the level needed to read tire pressure sensors. No tire pressure indication solid or blinking has been observed.
9) I tried sniffing car's CAN bus at OBD2 port while pressing key lock/unlock buttons.
When car responds, there is a number of messages all starting with "40 80 11 01 0F 0F 0F..." on the bus.
But when the car ignores the key, there is no communication over CAN bus at all no matter which key is used.

Based on that, my belief is either
1) TPMS stopped working (unless it sends messages not over the CAN bus but in some other way).
2) Yes, two keys stopped working simultaneously.


Did anybody manage to resolve the issue?

Is there any way to test if a key actually emits any radio signal?

Among simple things to try I'm considering disconnecting AUX battery for some time to let all the modules to reboot.

I'd appreciate any advices/ideas! Thank you!

 

Ok, for my personal case the problem is resolved.

I "load tested" 12V AUX battery and both remote key batteries.

For 12V AUX battery normally voltage is 12.6V. If I turn head lights on with key out of ignition, voltage drops, but not too far.

For both coin batteries I used a 100 Ohms resistor across battery terminals and measured current flowing through it.
For intermittently working key (works after the car is driven for a while) the voltage with no load is 3.046V. With load applied it drops down to 1.6V and the current flowing through is 16mA.
For the spare key which wasn't used for 6 years the voltage with no load is 3.334V. With load applied it drops down to 0.46V with current flowing through of 4.6mA.

For me it is still very counterintuitive that for a battery with higher voltage with no load (3.334V) the current with load applied is 4 times smaller than for a battery with lower voltage (3.046V).

So, it is the complicated battery chemistry issue here. For the spare key, even though the battery wasn't used much and it's preserved its original voltage, it's lost the ability to provide any significant current.

As for the key which works intermittently, my explanation is the most likely reason is the temperature variations. When the car is driven (in California central valley) the temperature is well over 100F. The key heats up. After the car is locked and left sitting, the key cools down in my pocket. It probably gives its chemical composition a little "boost" and it makes it working for some time.

I've replaced 2018-type 3V batteries in both key remotes. It made them work. I hope it may help to resolve someone's trouble.

 

I have a 2015 Prius C 2....This past Friday, I had my tires rotated and balanced and one of the tires reseated...Somehow with the reseating the tire, the TPMS system had to be reset. This morning (Tuesday) I discovered both my keyfobs (only has lock/unlock/panic buttons) did not work on my car....I manually unlocked the drivers door, then cycled the lock/unlock buttons on the door. Opened/closed the 4 doors and hatch. Keyfobs are now working...

 

check the 12v health

 

This only worked temporarily.....I actually had to change the batteries in both keyfobs before either would work...now both work fine (after dozens of locks/unlocks).