Opening and starting car with dead key battery (KEYED ignition)

I have a 2014 Chevy Sonic with a keyed ignition. I’m not clear on whether I have a transponder or not. I have a switchblade key in the fob.

The other day the remote failed to open the car door. I used the physical key to open the door and start the engine. The alarm sounded when I opened the door with the key. The alarm stopped when I started the car. The remote is now back to working normally.

I’m going to replace the key battery in case it’s failing. This incident may also have had something to do with recent hard rain followed by a flash freeze—the doors were frozen solid. I thawed the doors with a hair dryer and drove a couple of times with the remote working properly. This time there was no reaction at all when I pushed the door button on the fob, as if the key battery was dead.

Question: Can I always count on being able to open the door and start the engine with the physical key if the key battery is dead?

I ask this because I also have a valet key that usually works to open the door if I’ve lost my keys, but on one occasion it failed to open the door. This makes me think that door locks are more than just mechanical and they can fail if something goes wrong electronically. I don’t want to get stranded in some remote place and be unable to get into my car with a physical key.

My question is about the regular switchblade key, not the valet key. I know the valet key cannot be used to start the car.

Wrong , the valet key will open the door and start the vehicle . It will not open glovebox or trunk .

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No. The lock could be frozen up from disuse. The car could be broken so you can’t count on the physical key. You can count on the physical key if the battery in the fob fails… which is really what you want to know.


My particular valet key will not start the car. Maybe valet key is the wrong word. It’s a spare that is intended only to open the door—a cut blade, not attached to a fob, not programmed.

Then something is wrong with the key . Don’t you have 2 remotes ? Do both of them work or not work .

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Well, true, there are conditions that would prevent the key from opening the door, like ice in the lock. So yes, I mean can I count on the physical key when the key battery is dead?

If I’m away from home, I only have one remote on my person. I would only be able to test the second remote if I happened to be at home when the first remote failed.

If you have not put new batteries in either FOB do that as they are 8 years old .

The physical key is for opening the door if remote does not work . I don’t know why you are so worried about it . You might have a lock smith lubricate the door lock if it makes you feel better .

I am out of here .

Asked and answered…

I suspect that this varies somewhat from one make to another, but if my key fob battery goes dead, the Owner’s Manual directs one to extract the physical key from the fob, open the door with that key, and then hold the key fob against the “Power” button on the dashboard while pressing that button.

Mine is obviously not a “keyed” ignition, but it might be helpful for those with keyless ignitions when they run into a problem.

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Most owner’s manuals cover this situation specifically. Does yours not?


I would be extremely surprised if it did not.

Ha, so it does: “The key that is part of the remote keyless entry system can be used for the ignition and all locks.” Thanks for that reminder.

Someone asked why I’m so worried. I spend time in remote places in all seasons. I need to make sure I’m as protected as I can be against key failure.

The transponder in the key and the ignition do not rely on the battery in the keyless entry transmitter, energy is sent from the immobilizer antenna to the key to enable verification. You can remove the battery, the ignition immobilizer will still allow the engine to start.

The intrusion alarm will sound if you unlock and enter the vehicle without using the RKE transmitter, but this is a separate system and as you saw, the alarm is disarmed after the ignition is switched on.

Since this information is in the owners manual and everyone except George has immobilizer keys, everyone should be able to explain this.

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All I will say is guard your fobs like they are gold and don’t lose them. Fobs wear out and at least one is needed for programming new ones. But the physical key should always work. I change fob batteries once a year. You can not rely on getting a message that they are low. Costs a few dollars and ten minutes. I change all my batteries around the lull in the new year. Easy to remember.

I recommend that people invest a few bucks in a Faraday Box for the storage of their key fobs. My car “recognizes” me when I approach it in the garage while carrying the key fob, but then I experimented and found that it also “recognized” me when the key fob was sitting about 10 feet away, in my home.

When the vehicle “recognizes” me it turns on the interior lights and the lights inside the exterior door handles, and I quickly realized that this would run-down my car’s battery, and likely also the key fob batteries. For ~$20, I got a decent-looking Faraday box, plus two smaller soft Faraday cases, and I verified that even if I am standing next to the vehicle with the fobs encased in the box or the soft case, the car doesn’t “recognize” me.

This precaution also helps to prevent theft if my car is sitting in the garage with the garage door open.

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On my Lexus, the fob can be turned off by pressing the unlock button twice while holding the lock button, which is quick and easy, so that’s another option for any cars having a similar feature.

What model year is your Lexus?
I’m not sure that this will work on a 2022 model, but I will give it a try.

I have a large Tesla coil i built some years ago. We should test to see if your Faraday box would block against that radiation. :wink: