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MX5 Miata Tech Forum

Keyfog not working (with new battery)

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Grouch Hal Smith
Citrus Heights, CA, USA   USA
2011 Mazda MX-5 "My Baby" ~ For Sale ! ~
My backup keyfob doesn't work, so replaced the battery. IT STILL WON'T WORK! Any suggestions (other than pay BIG money for a new one from the dealer/factory? Is there a code or something else that has to be done with it?

Edited 1 time(s). Last edit at 2018-03-15 01:47 PM by Grouch.

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davzway David W
Fort McCoy, FL, USA   USA
Have you checked the coin battery to see if 'new' battery is charged? Many battery retailers sell OLD stock until gone, and having just received 'NEW battery, CR2025 for latest Mazda Advanced Keyless system.,, NOTHING on the package of FIVE (5) batteries says anything on date,, back has copyright date of 2016 but nothing on expiration date, Will be checking CR2025 on battery tester when back from trip.. Did go nearly six years on one and seven on other keyfob for 2011 Miata before the 'fob' stopped working.

Having CHECKED EVERY FUSE (BOTH inside and outside fuse box) for bad fuse, and checking Coin Battery being fully charged, and NEW battery in car, and IF KEYLESS ENTRY SYSTEM still doesn't work, may need to go to dealer to track down the problem.

Could check if there is a 'CODE' for the keyless entry system and having the plug in TESTING Equp, might be able to check yourself, fixing another issue.

1. Battery can go bad instantly, working one minute and not the next. Same goes ESPECIALLY for KeyFob (or any electronic device), working one minute then quits, REAL bad issue is electrical problems that are INTERMITTENT ,, then it needs to NOT work while on test bench to EVEN FIND out or hope to find what is wrong.. sometimes cost of doing so. exceeds value of object having issues.
2. Key Fob battery checked, if GOOD put in Key Fob, not working try MULTIPLE battery, and IF multiple GOOD batteries still don't make Key Fob work, ODDS are problem is elsewhere, NOT Key Fob, then it's CAR SYSTEM the Key Fob should actuate... first place is FUSE,, dealer should be able to advise WHAT CIRCUIT OR COMBINATION OF CIRCUITS that the Key Fob works to turn car on etc. Even if fuses LOOK good, replace ONE or BOTH Fuses on Key Fob circuits ,, 'Key Fob not working/ turning car on or unlocking door,, .......... REPLACE FUSES A SECOND TIME. IF that still doesn't do the job, may need DEALER or Mechanic with Computer Equip to check car as replacing Key Fob is NOT very likely to be the problem

THE TECH IS GREAT WHEN IT WORKS,, MORE TECH, MR. MURPHY (of Murphy's Law fame) has more chances to mess things up, and FUBAR chances are greater. Logic and Reason, there IS A REASON behind the problem and WHY.

Edited 1 time(s). Last edit at 2018-04-05 01:37 PM by davzway.

cdice Avatar
cdice George Dice
They do stop working. Do a search on Ebay or Google. A number of sellers take the guts from a used junkyard fob and put it in a new case and sell it for much less than a dealer does.

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davzway David W
Fort McCoy, FL, USA   USA
Second Edit: CR2015 battery (5-pack): NONE were all the way over in GREEN. Four were barely in Green, One just under line Yellow/Green. A NEW Panasonic Eneloop battery PEGS itself ALL the way over into Green, showing there is a difference on Fully Charged vs Marginally Green. Have found the Marginal Green where indicator Pegs barely in the 'Green' WILL operate the dinky small Media Streamer Sony Remotes that Sony is using today,,, where flashlight or object NEEDING the juice has marginally good battery.... WORKS, just not as well as it should.

Back to BUYING BATTERY FROM VENDOR KNOWN FOR SELLING FRESH BATTERY vs OLD STOCK, especially when referring to 3v Coin battery where NONE are rechargeable (none this reviewer is aware of anyway,,, ALL battery bought now are Panasonic ENELOOP, exclusively for AAA, AA, C & D (they have C & D Adapters using AA or 'AAA' battery.. NO store batteries around here except old flea market from friend,, at $0.10 or less, don't matter).

samsonsg303 Avatar
samsonsg303 Stanley Samson
Victoria, BC, Canada   CAN
1992 Mazda MX-5 "Red Lady"
1998 Chrysler Sebring "Converti"
2004 Kia Amanti "Monty"
2012 Lexus ES "My Hybrid"
I would suggest giving the service department and ask them if they have any ideas. Could be the new battery but probably not. You could try another one.

I suppose the fob could lose it's programming but that is rare.

Then again, you assumed the fob did not work because the battery was dead, perhaps the fob died.

davzway David W
Fort McCoy, FL, USA   USA
Finally got CR2025 battery that WAS nearly full charged,, NOT working then,, bad FOB . OR.. something wrong at vehicle where SIGNAL not doing or being accepted by vehicle,, should have already checked FUSE box on car for anything related to keyless entry.. then kick tire for all the tech.

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