Keys will not lock/unlock 2003 ML350

This can happen if you leave the key in the ignition, then it won't let you lock the doors electrically, you may be able to lock them manually, but then you will lock your keys inside.

if your key is not working to unlock door==try turning key over and then try to unlock door. I have had keys made for replacements and they sometimes don't work quite right one way but work just fine the other way.

to unlock hood with out being able to get inside; you need to reach up from under car and pull/yank on cable to unlock hood.

did you replace battery in remote fob, and do you keys have integrated circuits -- if so replace batteries.

Go through the sequence carefully.

- Sit in the car with all the doors shut and windows up with your key fobs (all your fobs need to be done at the same time)
- With one of your keys turn the ignition on then off and remove the key
- Press and hold the unlock botton and then press the lock button 3 times.
- Release all buttons and the locks will bounce up and down.
- Repeat this with the other key/keys (press and hold unlock and press lock 3 times, locks will bounce)

Note: Only switch your ignition on once, doing so again while programming will reset the process and you will have to start again.

the key should snap open. Once the battery is changed, insert the key into the door, while holding the lock key down press the unlock key five times.

Then hold the unlock key down and press the lock button five times

this should do it, if not, insert key into ignition and repeat the procedure

Programming
When
Key added or replaced. System malfunction.
How -

98MY
Keys can only be programmed using diagnostic equipment.
NOTE: A maximum of 4 keys can be programmed.
How - 99MY

Switch ignition ON. Insert key to be programmed into driver's door lock. Lock vehicle manually. Press lock or unlock button. Wait at least 1 second. Press lock or unlock button again. Vehicle horn sounds to indicate correct programming. Keys can also be programmed using diagnostic equipment
Above is how to re-programme a replacement key/remote

buy new remotes then have the keys/remotes reprogrammed.as your celica has a rolling code once done, only you can start it with your remotes/keys.(a rolling code means that every time you lock the car with the remote one of the two codes in the remote changes,so only you can start the car)

I never thought about this before, it may be normal on some vehicles. I have been able to lock/unlock my 2003 without the key in ignition since it was new.

Initialize keys. Have all keys for the car with in reach. Get in car and close all doors. Put 1 key in the ignition and turn it to the key on engine off position and quickly turn it off and remove the key. With in 5 seconds press and hold the unlock button while pressing the lock button 3 times, after the 3rd press release the unlock button. If successful the door locks will lock then unlock. For the remaining keys you do not need to cycle the ignition just press the buttons as mentioned before.