Re: Engine Immobilizer and Key Battery

On 6/4/20 5:00 PM, John McGaw wrote:
> 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.
> 
Good idea, I think I'll do just that.

Yesterday I called the service departments at a few dealers and asked 
the same question.

Two said no battery required, one said he thought it was, two said they 
weren't sure. I appreciated the IDK answers- rather than just making 
something up!

-- 
Never underestimate the power of stupid people in large groups