Intermittent Keyless Entry Problem

[dfh]

I have a 2013 CMAX SEL with factory keyless entry that has worked reliably for the two years I have owned it.  As of a year ago, a Ford dealer assured me that all software updates have been installed, even though the liftgate doesn’t always open with a single swing of the foot or triggering the hand activation system (a problem I read which others have reported).  

 

However, recently the keyless entry system sometimes fails, even though the 12-volt battery is charged.  When it happened yesterday, I made sure to verify that none of the four door handles would unlock the vehicle.  However, the liftgate did respond when I depressed the pad under its handle, which also unlocked all four doors.

 

Sometimes, when I have used the mechanical key to open the driver’s door, a beeping starts as the door is opened.  Once, the beeping ended with the horn sounding; another time when I quickly positioned the fob near the start button, the beeping stopped without the horn sounding.

 

Still another time the doors unlocked when I touched the mechanical key to the metal where it is supposed to be inserted, perhaps the result of static electricity transfer to the vehicle.

 

Other times, the doors unlock when I grasp the driver’s door handle.

 

The 3-volt CR2032 battery in my only fob measures 2.96 volts.

 

It hasn’t rained during the period of keyless entry failures, so water intrusion into the hardware is not a candidate culprit.

 

Does anyone have any troubleshooting tips or has anyone had similar CMAX behavior?

[Mike G]

I think that your fob battery is due to be replaced. I just checked the voltage on a new CR3032 and it measures 3.21 volts.

[stolenmoment]

Yes, mine was behaving like that as well, the fob button range got progressively smaller, and then the door-handle unlock started failing, etc.  Replace the battery, it's easy.

[dfh]

Thanks for the replies.

 

Replacing the battery has apparently solved the problem, though I am surprised that it did so because of the following observations:

 

1.  Once the door was unlocked with the mechanical key at the being of the day, then the presence of the fob would lock and unlock the doors normally.  Why would it take a stronger battery to perform the first opening of the day but not subsequent openings?

 

2. After the first opening with the mechanical key I tried using the buttons on the fob to lock and unlock the doors, first when I was next to the vehicle, and then repeatedly as I walked away from the vehicle.  They were still operational when I was 36 feet away and out of space for a longer unobstructed path between fob and vehicle.  Assuming the fob's broadcast antenna is unidirectional, the intensity  of the radio signal decrease as 1/distance squared.  It hard to understand why the fob buttons still worked with a mildly discharged battery when I was 36 feet away unless the keyless entry signal is different from the button signal (which is possible, since it broadcasts continuously and the energy stored in the battery is limited).

 

The next time my keyless entry system fails, I'll try the fob button to unlock or lock the doors, not the mechanical key.

[stolenmoment]

I suspect that the keyless entry works via near-field signalling (like a card you tap or wave rather than insert somewhere), rather than the fob broadcasting anything, but it may be amplified by the fob's battery (guessing). It *may* have a different voltage threshhold before it works properly.  Guessing!  I'm a software guy who does little bits of electronics as part hobby work.

Edited June 27, 2021 by stolenmoment