This is for a 2008, G35x sedan.

I have been having this issue for a while, so I do not really know when and why it started. To keep note, the only things I have done electrical wise is I have an amp power cable that travels past the BCM to the trunk, and I tapped a fuse under the steering wheel, Meter (BAT), to power some auxiliary lights through a switch, and I am not completely sure if this is effecting the fob or not.

Anyways, my issue is that most of the time my car would not detect the key fob. Sometimes it does, but says that it has low battery, very rarely this doesn't happen at all. This issue is occurring on both my key fobs. I have changed batteries multiple times and adjusted the contacts and flipped the battery many many times to no avail.

I usually have to insert the key into the key slot to start the car, as moving the key around the cabin does not seem to do much in some cases. The main thing I noticed is that the car has the most difficulty opening via the door buttons, as well as the trunk button. The key buttons work often, but at a noticeably less range. Going along with this, I usually press lock and unlock multiple times by habit by now, but in some cases it does not detect at all. Sometimes I do actually get better response moving the key closer to the dash, and even better from the passenger seat or rear seats, but definitely the most trouble in my pocket drivers seat. Oddly enough, it does not detect at all anywhere in the car if a door is open, so I usually have to close all doors before being able to try to turn the car on.

I have tried changing the antenna that is under the head unit, but it did not change at all, I also tried changed the keyless entry module behind the glove box, but I don't believe that did anything either. Any ideas besides swapping the BCM?

 

It could be intermittent power in the FOB itself.
Try cleaning the battery contacts with an eraser, bending the contact pins, or try a new FOB.

 

Appreciate the suggestion, but as I mentioned, I tried bending the pins, but both my spare and regular fob are experiencing the same issue.

 

How exactly did you tap power for that amp. If you used a C tap that could be the issue. Solder/splice probably not the issue but the electronics associated might be the issue.

Try unplugging the amp and see if it's still malfunctioning.

I would try one more CR battery, buy a new one from a store, just to rule out that maybe you ended up putting a discharged battery back into both fobs. Especially if you already had these batteries and they came from the same package. Sometimes you just get a bad batch of batteries especially those trash "Amazon Basics" ones...

 

The amp is wired directly to the battery, it is not taped to anything. The wire I have tapped to the METER fuse is taped via a T-tap or a quick wire splice tap. This wire is connected to a switch, which goes to some auxiliary lights (halos and demon eyes on the headlights). And I am very sure that the battery is not the problem for the fobs.

 

What fuse is the "Meter" fuse and is it always powered or only when the ignition is on?

The problems you describe would normally point to the fob as the cause. But because both of your fobs are effected, and it is both the fob buttons and the car's "call and response" door button communications, this seems unlikely. Unless as Mike suggested, somebody sold you a case of already weak cr2032 batteries...?

I believe the lock / unlock fob buttons communicate to a specific "remote keyless entry module" which in turn tells the BCM what to do. And the door buttons and ignition fob sensing antennas work directly with the BCM. At least that's my understanding.

So that makes me wonder if it's some kind of radio frequency interference? Some LED lighting has been found to transmit rf hash which can interfere. Also some cigarette-lighter power supplies have been known to cause this kind of weirdness. But these devices should not be powered until the ignition is on so they shouldn't interfere with unlocking the doors

I agree with everybody else and suggest you temporarily disconnect the power running to your amp and/or that tapped-off extra lighting power just to see if the car suddenly becomes more responsive to the fobs. Do you have a radar detector or dash cam attached to your rearview mirror?

Let us know what you figure out.

 

Alright so couple things, some good ideas. I have LED lights everywhere, glove box, map lights, car doors, etc.

I have both a radar detector and a dash cam attached to the windshield. I also had a cigarette lighter dual output charger, but none of that should be on until the car is on.

I am totally unsure what the METER fuse is for, when I yank it out, the cars electrical acts really weird, I forget what exactly happens, but its weird. I tapped this wire because I am able to power the extra lights WITHOUT turning the car ON or ACC. So it is always powered.

I will try pulling the ground for that connection, as well as the power for the amp tomorrow and I will see if it changes anything.

 

I unplugged pretty much everything. Took all my LEDs out, took out the grounds for all the wiring I did, and unplugged all the things in the car, dash and radar detector. I also tried taking the METER fuse out, and the key still is not working right.

 

D'OH! Sorry to have sent you on that goose chase but it sure sounded promising... You disconnected the power amp too, right? LED map (dome) lights? Could you humor us and try a fresh cr2032 battery in the fobs while your electrical system is temporarily back to "stock"? Can you remember when the fobs started acting weird, like after any specific mod? Or was it always like this?

I'm scraping the bottom of the barrel for ideas now, sorry. Maybe cleric has more?

 

Yea so, this is kind of wack. My door LED's were indeed the one's interfering with the key fob. I was rocking these UV lights from some website, and that was a big problem for the key fob apparently.

Also, very wild to me. When I said the battery was good, I was using a volt meter to check it, and it was showing 3V. I assumed that since it is a 3V battery, 3V is good, but actually it needs to be at ~3.7V for it to run correctly, so I got new batteries for both fobs and they are both good now.

 

Sometimes doing the simple stuff works.

With those batteries (and most batteries) it always has to be higher .

Just like your main 12V battery . At 12 volts it's dead . It has to be higher.

 

Thanks for the followup. Wow, so you did find some interfering LEDs after all. Well done.

And the fob battery thing is irritating, but your car will let you know when the fob battery is low. I can't find an '08 book right now ... but from '09 on it would display a message directly on the LCD screen with a picture of a key and a low battery indicator.

Thanks again for letting us know you fixed it.

 

I should have updated this a while ago, but it was not the LED lights, I have turned off the ones in the doors and the problem is still occurring.

Though, I have new info, the car does not detect the key until I turn it on, then it says key battery low, then the warning goes away after about a minute.