Re: Engine Immobilizer and Key Battery

On 6/3/2020 7:34 PM, Wade Garrett wrote:
> On 6/3/20 5:56 PM, Darryl Johnson wrote:
>> On 2020-06-03 5:07 p.m., Wade Garrett wrote:
>>> Got a 2017 Forester with remote keyless entry but NOT push button start.
>>>
>>> If the battery in the key cap drains so low that the key push buttons 
>>> won't lock/unlock the door, can the engine still recognize the 
>>> immobilizer chip in the key and still start/run?
>>
>> When the battery in my Audi's key got too low, the car started, but 
>> wouldn't keep running. Plus I couldn't use the remote to lock/unlock the 
>> doors.
>>
>> Fortunately, it was a simple job to replace the button battery in the fob.
>>
>> Obviously, an Audi is not a Subaru, and things may well be completely 
>> different, but I wouldn't take the Subie too far away from alternate 
>> transport until you get that battery replaced if I were you.
> 
> Mine isn't a fob. It's a metal key you insert into the ignition switch on 
> the steering column and twist to start the car.
> 
> It looks like an ordinary key but with a big plastic head that has lock, 
> unlock and emergency horn-blow buttons and a button battery inside.
> 
> I guess my question really is does the immobilizer system require the key 
> battery to still have a charge...

Well, chipped keys are common and many (most?) of them don't have a battery 
or buttons and they still manage to work because the car's ignition lock 
has a coil around it which signals to the chip circuitry in the key body. 
This is called a transponder IIRC. The big question is does your key use 
this basic method for this single purpose or does it combine all of the 
electronic functions into one. I know for certain that my 2018 OB with 
keyless start and remote buttons on the fob still has the transponder 
function built in and the manual says that to start the car when the fob's 
battery is dead you need to actually use the end of the fob to physically 
press the button (so that the car and fob transponder are oriented 
properly, I presume).

I guess one sure-fire way to find out would be to remove the battery and do 
the test, being careful not to lock yourself out somehow.

-- 
Bodger's Dictum: Artifical intelligence
can never overcome natural stupidity.