My lock and unlock switch on the key fob starting having issues about a month ago. I could unlock it but not lock it. Now both buttons stopped working. Just tried troubleshooting it. New fresh pair of CR2016s from Duracell. Didn't help. My leds are both lighting up as I push the buttons. So I tried a computer reset with ground on the positive side of battery to drain computers. When that didn't work tried reprogramming. Cannot get the car to chirp in programming mode after following the procedure of trunk open drivers side open and valet 5 times. Check continuity on the valet switch and its fine, closes when the switch is pushed. The locks and alarm work fine if I use the key to lock and unlock. Chirps too when I do it.

Any more ideas? Bad key fob? I've taken it apart and looked at the little PCB board under a micro-scope couldn't find any signs of damage. I have also recently replaced the microswitches and they are working fine, checked with ohm meter and the lights are lighting up.

Update just did a quick check with SDR# and it is transmitting on the upper end of 433Mhz when I push the button which is the right frequency for my VIN which is later model one (761XXX)

 

OK I figured out the problem. First of all the car wasn't going into learning mode because I didn't have all the doors unlocked, just the drivers side. So once I got it into learning mode, it wouldn't recognize the key fob button when pushed. So I decided there was a good chance the key fob was bad. Checking ebay, I see there are few available and NOT CHEAP!

So I opened this one up and took a look again. I remember the board being clean on the top when I installed the microswitches and at the time I thought it was a single sided PCB. But it hit me there has to be a programming chip somewhere and its not top side. So I de-soldered the two battery pins in the middle and lifted the PCB out of its housing and was very surprised to find an awful looking back side that was corroded from water damage. So with nothing to lose now i scrubbed it real good with 99% ISO and a tooth brush to get most of the corrosion off, then reflowed the components with plenty of flux to try and clean up the solder joints without dropping components off the other side. Don't do this unless you are very comfortable reflowing SMD components with hot air.

Put it back together and didn't even have to reprogram, works better than before with better range now. Corrosion never really goes away so might have to do this again in a few years, but at these low voltages shouldn't damage anything.

Hope this helps someone.


What top side looked like when i replaced microswitches (and why I assumed the fob was fine):





Before back side with water damage:









And after cleaning and reflowing:







Also this is what the waterfall on SDR# using a standard cheapie RTL-SDR USB device with standard antenna and default settings should look like after pushing the buttons on the key fob a few times. A much stronger and pronounced signal as you can see.

 

Thanks for the detailed description.

I am having a similar intermittent problem. I want to eliminate the fob. The usb device for testing you mentioned. Is it something like this:



also what software did you use to measure the signal?

thanks!

 

Yes that is similar and would likely work the same as mine. The exact one I used was this:

Since mine was a later model 96 I am on 433Mhz, but I think most X300s are down around 315Mhz.