The door locks on my Mercedes 420 SEL lock

Probably has 3 or 4 of them in the exhaust from the header down past the catalytic converter. Your check engine code should have stated which one. Anyway, an easy fix, might need special tool, check it out, Hope this helps.

I've never heard of a car without at least a key lock on the driver door. Unless it's a custom car, but they usually have a hidden button to push to open the doors. The only way to get in, other than calling a locksmith or breaking a window, is to use a "burglar bar", or as some call it, a "slim jim", to try and hook the opening or door lock mechanisms inside the door.

sounds like the battery in the remote is old and dead and needs to be replaced. ( could also be the electric door lock fuse ).
if you are also experiencing trouble with your door locks themselves turning - then try and spray some teflon or silicone base lubrication in all the locks to wash out any dirt or debris.

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If its never been done, just due to age it would be good to due it and guides before any issues developp.

This could be caused by a faulty Crank position sensor. The computers are expensive for this and not something that commonly fails on these. Have the fuel pumpchecked for operation and pressure. Check for spark at the plugs. Then we can procede further if you would like.

Central locking fuse or pnuematic pump under rear seat has gone bad.

15486372 With the number on thru 4 cylinders on the right bank and 5 thru 8 on the left bank as seen from the drivers seat.

Needs a New Flasher. This is located in the center console somewhat near the ashtray.

Call the Mercedes I-800 number on the sun visor. Give them the Vin number and they will give you a 4 digit number assigned to that Vin. Input code in radio unit through (1-0 radio buttons)... Press "seek". Simple

hi friend,

go to
www.Books4Cars.com
or
www.DataManuals.net
or
www.autosmanual.com/.../mercedes-benz-operator’s-manual-ml-320-se-420-sel-500-sel-pdf.html -

thank u for using fixya

regards,
sivaranjini