OK, this has happened a few times. My '14 RX starts just fine, THEN the message 'key not detected' pops up. The first couple of times I turned the car off, restarted it & the message went away. Happened again today after starting the car and then after about a minute it went off. I had changed the battery in the FOB after the first few times, just wondering if anyone else has had this type of problem.

 

I had a similar issue a while back in my RX350 when my key fob battery was weak. I swapped batteries and it still happened because my replacement keyfob battery was weak as well. Sometimes those batteries can be duds out of the package if too old or defective.

I would try using another fresh battery in your key fob. If possible check the keyfob battery voltage with a battery tester; that is how I found out my replacement battery was dud.

 

Battery tests ok, I've switched FOBs & see if it continues. If not I will have the FOB checked out.

 

The fob's circuit board and electrical contacts may need cleaning with alcohol and a Q-Tip. I have had to do this with a couple of our previous vehicles as they aged.

 

I cleaned the circuit boards on both FOB's, made sure they both still worked and left for a doctor appt. Started the car, no problem. Was parked for about an hour, and started the car up, again no problem. As I was backing out of the space got the 'key not detected' with the orange triangle message. Lasted for a minute or two then went away. Very strange. Called my local shop that has done work on our vehicles & they stated that was not something they were equipped to handle. Not real keen on taking to the dealership if I can avoid it but don't want to get stranded someplace. Oh, also checked the new FOB batteries just to make sure they were good & both pulling 3V which they were.

 

I don't want to be too technical but a 3V lithium coin battery read 3V is very weak! We need to eliminate all the basics first.

 

New Duracel batteries and just tested to make sure they were good, tested over 3v exp 2032 (which we know would be dead by then!). I had actually just replaced the batteries earlier this year but went ahead & bought new a few weeks ago and put those in- just in case. It is just strange, nothing has changed, no new phone or parking situation, etc. where electronics could interfere. It can happen anywhere but only on for a minute or two after the car is started. Example a few days ago happened in the garage, started the car & looked at the dash- no message. As I went to back up, it came on but then went off before I finished backing up. Today with a different key fob/new battery, it happened it a parking lot. Came on & finally went off after driving maybe a 100 feet. No issues in starting the vehicle so far just don't want to end up stranded at some point.

 

Well, you may have an wireless key radio module issue.

It seem like you may have to take your RX350 to an dealership and have it replaced since it may require programming related to your RX350 VIN number.

 

This may be helpful; after we purchased this car took the 2 car fobs into the local Lexus dealership and parts gal there replaced fob batteries for free and said to bring them back anytime for courtesy battery replacement if either stopped working correctly. Same day upgraded the car battery to an aftermarket AGM which is supposedly easier on sensors and bulbs and haven't had any electronic or bulb issues so far.

 

Checked around and found an indie shop that was highly recommended that worked on Lexus. Went & spoke with the tech & he said since it is so intermittent to basically not to worry about it at this time. He could run diagnostics but chances are nothing would show & would be a waste of money at this time. If it comes on & stays on or comes on each time vehicle is started to bring it in so they have something concrete to work with. Nice to see someone honest & not spend a couple hundred with no results I know the Lexus dealership would have taken it & billed for checking most likely telling me they can't find anything.

 

Wondering if you've performed a soft or hard electronics reset on the car by disconnecting car battery and following the sequence for either ?

 

No I haven't. Is there a different way to do this other than disconnecting the battery? I know when disconnected I believe I have to 'retrain' the windows, etc...

 

Both soft and hard reset involve disconnecting the car battery, when I recently replaced this car's battery and disconnected positive and negative connections for about 5 minutes the only item that had to be reprogrammed was the clock and no problems with windows and likely considered to be a soft reset. After starting car the first time after replacing battery the car stopped by itself but restarted by pushing starter button again without issue. Anyway either types of resets may get rid of electronic glitches and this just offered as a suggestion as something to try to remedy your problem, interested to know what the solution is though. Following video gives instruction for battery replacement soft reset;

 

you might have a signal Bluetooth interruption try to keep your keys away from wireless headphone cases or magnets or phones in the same pocket

 

I've always put the keys in the spot next to the cupholders. Also have same phone for couple of years in a holder up on the dash, as this just started within the past few weeks. Still have to do a reset with the battery and see if that works...it's just that it doesn't happen all the time, just every now & then-very strange.