Missing key fob battery - will car start?

[rpdm]

Hi,

This is referring to key fobs with remote unlock / keyless start, like this one: https://www.transpondery.com/keys/ford/ford-intelligent-key.html 

My son got a 2nd hand Ford B-Max and the key was dodgy (intermittently worked) so I had 3 new non-OEM keys programmed by a reputable Auto Locksmith.  All work fine (unlock/lock/start car), but I thought I'd check that they work ok without a key fob battery (to pretend the battery was flat) in the backup key position.  They didn't.  I then tested 2 other Ford cars we have:

2011 Ford Galaxy = will not start if battery missing from key fob (backup position under removable cap on steering column).
2013 Ford B-Max = will not start if battery missing from key fob (backup position on side of steering column).
2019 Ford Ecosport = will start (but key fob is completely different design).

Being electronically minded, I used the original Ford (dodgy) key fob and measured the AC voltage present across the key fob's inductive charge coil (the round thing on the PCB in the link above) when in the above places.

2011 Ford Galaxy = around 0.4v
2013 Ford B-Max = around 0.7v
2019 Ford Ecospot = a whopping 18v!

So my question is whether the older Galaxy / B-Max should have started with a missing battery?  If so, then I guess both of their backup key inductive-charging positions are faulty - which is unlikely.

Personally, I think that the older key fobs rely on a dead (low voltage) battery to be a slight capacitor, or perhaps a 'boost' for the voltage from the backup position's inductive charger.

Does anyone know if the 'backup' keyless-start system uses the same codes as the 'normal' keyless-start system?  (I.e. Same codes, just the backup position provides the power, rather than getting power from the 3v CR2032 battery.)

Either way, the B-Max is in for timing belt replacement (1.0L Ecoboost = ouch!) in a few weeks, so will ask the Ford dealer then.

Looking forward to any comments, in particular if anyone tries out removing their key fob battery to see if the car will start without it.  (Note to also press a lock or unlock button after removing the battery, to get rid of any residual charge, to make the test valid.)

Thanks!

[StephenFord]

15 minutes ago, rpdm said:

Looking forward to any comments

One of my 'factory' supplied keys does not have a battery! It's a simple key only (no 'remote' functionality) , but as with all keys, if they start the car they'll have a built in chip which is passive, and the proximity of it to the ignition barrel will deactivate the immobiliser...

[unofix]

I suspect the keys that will not start the car with the battery removed are both missing the passive PATS transponder chips.

In Ye Olde days the Ford keys had two separate and fully independent parts. (a) The passive transponder chip, and (b) the active transmitter for the remote lock/unlock. Neither function had anything to do with the other.

When the lock/unlock button was pressed on the keyfob the transmitter, powered by the battery would send a signal to the cars receiver and the doors would lock or unlock as requested.

When the key was placed in to the ignition barrel then an inductive loop would read the passive transponder chip that was embedded in the key, no battery power required.

Now we have to fast forward  to the 21st century and the advent of keyless entry and more importantly keyless ignition. The new keyfobs still have a passive transponder chip for emergency use but for 99% of the time it's never used. Now the keys use a rolling code generated by the key which is transmitted to the vehicle each time the key is inside of the car. This does use the battery inside the keyfob and it happens automatically. The receiver picks up the code from the keyfob and allows the car to start. The built in passive transponder chip is not required and is not read.

In the event of the keyfob battery being missing or totally flat then the keyfob has to be placed in the emergency location. Then like in the Ye Olde days the inductive loop picks up the code from the transponder chip and allows the car to start.

[rpdm]

1 hour ago, unofix said:

I suspect the keys that will not start the car with the battery removed are both missing the passive PATS transponder chips.

The Galaxy key is original and looks exactly like the one in the link.  The replacement keys from the Auto locksmith look almost identical inside as well.  So I don’t think they’re missing any vital components, but possibly two chips are merged into one. 

From what I know the main “code” chip on the PCB handles both the active lock/unlock buttons and the passive keyless start. So there’s only one chip for this on both the original Ford key and the replacement keys.

As I understand it, lock/unlock is sent over a UHF link (433MHz) and the passive keyless start over a low frequency (and therefore low power) link (possibly receiving a LF request for a code and then transmitting via UHF). 

Would be interesting to know other people’s experience of this (if they fancy removing the battery). 

[unofix]

3 hours ago, rpdm said:

but possibly two chips are merged into one. 

No, they are two separate items.

3 hours ago, rpdm said:

The Galaxy key is original and looks exactly like the one in the link.

Has the PATS identity of the key been coded in to the car assuming that the transponder chip is present ?

3 hours ago, rpdm said:

From what I know the main “code” chip on the PCB handles both the active lock/unlock buttons and the passive keyless start. So there’s only one chip for this on both the original Ford key and the replacement keys.

That is correct. One chip handles both the remote locking and the keyless start.

 

 

[rpdm]

On 3/11/2023 at 11:22 PM, unofix said:

Has the PATS identity of the key been coded in to the car assuming that the transponder chip is present ?

That is correct. One chip handles both the remote locking and the keyless start.

Firstly, I appreciate all the info you're providing - but I'm still a bit confused.

The genuine Ford key fobs (Galaxy & B-Max) should have the transponder to allow the key fob to be placed into the backup location if the key fob battery is dead.  It's mentioned in the manual and various places on the internet, so should be there.

Inside, they only have 2 chips - one I'll call the transponder chip, and the other is the UHF transmitter chip.  From what I can tell, the main chip is similar to this one:
https://www.nxp.com/docs/en/brochure/75017275.pdf 

In that link, you can see that the chip should have a built-in backup transponder.  It's not a separate transponder chip for this purpose.  That link's schematic matches the PCB for all the key fobs I have (OEM & non-OEM), as it has the 3x inductive low-frequency coils, the main transponder chip, the UHF transmitter (for long-range unlock/lock), plus battery etc.

Apparently, when the Auto Locksmith added keys to the B-Max, it adds two 'codes' for each key fob - one for keyless entry, and one for keyless start (the latter of which must surely be the Passive Anti Theft System PATS code you're referring to).

From what you're saying, there are THREE security codes, one each for:
1. Keyless entry (unlock/lock/boot).
2. Keyless start when the battery is working.
3. Keyless start when the battery is dead and placed in the backup location.

From what I understand, codes 2 & 3 are the same, they're just accessed differently (battery good vs. battery dead)?

[unofix]

3 hours ago, rpdm said:

From what I understand, codes 2 & 3 are the same,

No they are different.

The normal code that the ignition receives from a working keyfob is on a rolling algorithm and changes.

The emergency transponder chip is passive and the code never changes for that.

[rpdm]

Got a comment from my Ford dealer: "... the Eco-sport is probably using a different system hence working without the battery (keyless system) whereas the B-Max and Galaxy won't work if the battery is missing from the remote and is normal."

I'm guessing that the 'back-up' key fob locations shown in the Galaxy & B-Max manuals are nothing more than getting the remote closer to the car's antenna for the keyless start system, for cases where the battery is running low, rather than completely flat / missing.