"key not detected-insert key into slot" or something to that effect. We JUST put a new battery in the FOB last week and all was good for a few days. Now we are having trouble with the car recognizing the key, doors not opening without actually clicking on the unlock button on the FOB, etc.
Any ideas?

ETA: BTW, fresh car battery as of about a month ago. No other electronic issues.

 

what's the voltage reading of the FOB battery? Have you tested it? Sometimes the tangs in the fob are in a state of constant connection and drain the FOB battery. If it were me, I'd start there.

 

Thanks, I will check it out.

 

I have found that discount/generic CR2032 batteries don't cut it, also name brand ones from Amazon I have had struggle. I only buy them at a brick and mortar store to ensure tighter supply chain so they aren't old or counterfeit. And definitely not the dollar store!!! I had persistent issue with my Fob and low battery warning until I changed my buying habits.

 

You have a 2007 XK, so no doubt your Smartkey fobs have had the batteries changed many times. After 14 years, it's likely that copper prongs in the battery compartment have stretched and are not making good contact with your new CR2032 battery.

Don't try to bend the prongs, as they are fragile and if they break you'll need to buy a new Smartkey.

Instead, buy a new CR2035 battery. It's identical to the CR2032, except that the CR2035 is slightly thicker, 2.35mm compared to 2.32mm. That additional thickness should make better contact with the prongs, and won't interfere with closing the case.

You should also keep a spare CR2035 battery in your glove box, just in case. I buy my fob batteries locally from national chain stores so I can check the expiration date and know that the brand is authentic, and not a cheap Chinese knock-off.

Good Luck!

 

So you guys seem to think this is a key FOB battery issue. Interesting, considering the buttons on the FOB work flawlessly from long range i.e. trunk unlock, doors unlock and lock, etc.

 

Not necessarily. It's just the quickest cheapest thing to eliminate. I assume you only have the one FOB.

Any new devices in or around the car that may be giving off a radio signal? Could be interfering with the FOB.

 

We have two, but the spare has been dead for a while. Need to put a new battery in it and try it. Just too busy. I would be much more motivated if it were MY daily driver.... hehehe.... I need to get on the stick and solve this for my dear wife.

 

I made exactly the same experience.
Many issues with a new cheap no-name C2032, changed it for a branded one that did cost 5 times as much, problem solved.

 

my ipod used to interfere with key detection (yeah, who knows) but it was sporadic and i haven't seen it happen in a very long time. i think the ipod cable was just loose due to how the contents of that compartment were arranged.

 

Take the Smartkey out of your pocket, put it on the dashboard near the speedometer and try to start the car. You might get lucky (but I doubt it). If that doesn't work, watch this video.

Although it's a Land Rover, it shows what the technician went through to pinpoint why "Key Not Found" and it wouldn't start.

Worth watching:

 

Just an update for everybody. I went to Lowes and purchased a 4-pack of Duracell 2032s (they did not have 2035s, and I question their existence after doing an online search). I cut out two disks of heavy duty aluminum foil to build up the thickness of the battery. Did that for each of our 2 key FOBs (so, 4 pieces of foil, total). They both now work flawlessly.

 

You are right! I searched extensively online and it appears that CR2035 is no longer being made. CR2050 is available, but I don't know if it will fit under the cover.

 

For nearly any CAR problems; IT'S THE BATTERY!!!
For nearly any KEY problems; IT'S THE BATTERY!!!

 

It's always the first place to start because it's the easiest and cheapest fix, if it works. But when it doesn't ... It takes SDD, knowledge, experience, and a bit of Sherlock Holmes to figure it out, as demonstrated by the video in my Post #11, above.

 

Even dealer supplied and fitted (dont worry they were FoC) are rubbish and only.lasted 3 months.

Then googled 'best keyfob battery', it came up with comparison testing stuff and the top was the brand I boughr, 18 months later they're still working

 

Changed batteries 2 years ago on both fobs. They both stopped working yesterday, changed to new Vartas and all good.:-)

 

The early Smartkey design was improved with a re-design to the back of the case. The problem with the original is it doesn't hold the battery firmly against the contacts. The updated casing resolved this.

I replaced the casing on my 2007 XK and have a note of the P/N's as follows:

Case back - C2P17158
Button pad - C2P15135
Chrome trims - C2P15136

Your aluminium foil solution probably has the same effect as the more rigid case back.

Graham

 

in your efforts you should have found that even if the battery is dead in the fob, by placing the fob in the slot provided in the centre console, the vehicle will respond and start. If the car does not respond, there is another issue at hand. Glad it was as simple as a fob battery for you.

 

The keyless system seems to be very particular. Like the OP, my key would work flawlessly externally, from button pushes to unlocking/locking the door via the handle sensors. But once in the car it would be consistent low battery warning messages and/or require that you put it in the slot to start. For me it was easy fix, buy a better battery. Took a while to land on that solution, I had tried multiple changes from my pack of generic batteries before figuring out that they all were not a good match for the Jag key.

Fortunately for me I am in the KISS category (Keep It Simple Stupid) and always try the easiest most direct solution first, if not I would have been down a rabbit hole of new fob and/or internal module analysis!