Key not detected but the fob works!

[Ethan-tilly1]

Morning all. It's a 2017 Fiesta. The key fob has had a new battery and works to unlock the doors and boot but when I put it in the ignition it lights up the car but won't start the ignition and it reads " key not detected"

Any help much appreciated and thank you in advance
Paul

 

[tabijan]

Did you try a spare key?

Sixto
2014 SE 1.6 hatchback 135K miles

 

[Handy Andy]

Call up the console menu, see if MY KEY menu option can help you decipher this.

Why? A corrupt key code can usually signal a key fob has a bad Passcode to start the motor - but it will let you light up the dash but it can't let you start the car due to a fail in a loop-back test that tells the vehicle to allow START.

IT could mean the chip in the key-fob has failed it's not recognizing the key by the ID it emits. To fix that requires a supervisor key - so if you have a supervisor key and there is another one put away - make sure it (the other one) has fresh batteries because you may need to train the system - the system needs both Supervisor keys present and detected to reset the key and make the system recognize it.

 

[Ethan-tilly1]

Did you try a spare key?

Sixto
2014 SE 1.6 hatchback 135K miles

Yes the spare works fine. Any ideas please.thank you

 

[tabijan]

Buy a new key. I don’t know Fiesta keys specifically but typically there’s a wire coil in the key similar to the coil in an entry ID card. Doesn’t require batteries like lock/unlock features. A sensor in the car (PATS?) recognizes the coil and authorizes engine start. The coil can be damaged if you drop the key hard enough. With a working master key, what Handy Andy called a supervisor key, it should be possible to program the car to recognize a new key. Maybe get it to recognize the old key if it’s a programming hiccup.

At this point I’d check with a locksmith about a new key. You might get the old key working only to have it fail again. It might be possible to program the start aspect of a new key yourself without specialist equipment. You can program the lock/unlock features with instructions on YouTube, but that won’t start the engine. The blade of a new key will have to be cut to work with your car.

Sixto
2014 SE 1.6 hatchback 135K miles

 

[Handy Andy]

It may not have a means to turn a tumbler in the car, the key supplied with the fob can easily open the outer locks, but you need a tumbler (lock for the key to turn) to make the car start.

The issue around the fail to start is like what @tabijan is saying - the fob's ability to finalize the start process is corrupted.

So if the Car battery is fine, and another key starts the car - then any lockouts like PARK safety switch - can be ruled out as not the fault. So this goes back to the Fob itself and the ID it emits when polled - if it doesn't match whats in the cars own memory - it will not start.

To fix that requires a "Master set" of key the Owners manual and the MY KEY Menu refer to as Supervisor keys

 

[Ethan-tilly1]

Thank you all for the great feedback. Much appreciated 👏

 

[Handy Andy]

Ok, so you know...

The "Fob" itself is a transponder - meaning it responds to an inquiry from a transceiver which processes the codes received and if the key-fob has been dropped, the ID may be ok, but remember it's an RF (radio) transmitter - so if the electronics are damaged - the thing may emit a signal but if it can't transmit it correctly at the frequency its supposed to - the noise it makes the car thinks its trying to get fooled so it won't validate the response.

Door locks are one thing - keys are another.

 

[Ethan-tilly1]

Thank you.

 

[Handy Andy]

To help you more...

The key-fob itself uses those (Gosh Darn) Lithium coin batteries.

In mine they use 1 2032 - which is kinda' important due to several factors...

One - is their size...


But more important is their rated voltage at that size - for a given draw of current in mA

CR2032 can supply up to 200mA draw for a rated length of time RATED for 3 V
CR2025 can supply up to 165mA draw for a rated length of time RATED for 3 V
CR2016 can supply up to 90mA draw for a Rated length of time RATED for 3 V

So since you have a key that emits an RF signal - the 3V supply has to produce the ID and any other string of information in a manner the receiver can decode it using a receiver designed for being FM/PWM or AM or even DTMF on FM.

No matter how you look at it, if the Battery cannot supply the right amount of current - the system can trigger a fail and not start your car.

It's not a bad idea to recheck the supplier of your battery and just get another and try that one to see if it can work - I'd hate to know that this could have been fixed because the battery off the shelf was also dead or past-dated and expired - you just needed to clean and re-seat the contacts and use a new fresh battery to get your car back on the road.

The bad thing would be that the Cars Battery was good, it was the Keys Battery that was causing the fault.

So if you put in the correct ones - great, but if one goes bad or is not at 3V - it may be having higher output than 3V or less than 3V (which can be just as bad) - can cause the signal to become distorted when its sent - then the Door lock would seem to work because the PATS senses the control signal - but the START control it needs is not being recognized.