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Stan, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3526
Experience:  Technical support engineer
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I have a 2002 Mercedes A170cdi. the central locking has

Customer Question

I have a 2002 Mercedes A170cdi. the central locking has stopped working (all doors), by both remote and key. It will unlock by remote (if you lock it manually) but will not lock. The drivers door and boot will lock by key.

When you drive above 5mph it locks but as soon as you slow down to stop it unlocks again. Any idea what I could try. The hazard warning lights work, the remote when pressed flashes the indicators, the vacuum unit in the boot is dry and clean. George

Submitted: 3 years ago.
Category: Mercedes
Expert:  Stan replied 3 years ago.
Stan :

Hello George,
Please try to disconnect the vacuum unit for few minutes. It seems that a vacuum leak has been detected and only one central locking function is not working.
If this will reset the system- either there is a vacuum leak, or the vacuum unit itself is aged and too weak.

JACUSTOMER-k7p46btt- :

Hi Stan

JACUSTOMER-k7p46btt- :

Hi Stan
I have disconnected the vacuum unit for about 30 minutes and then reconnected and is has made no difference. When the car is moving the central locking turns on and off quite well so the vacuum pump works sometimes. My Mum had a problem with the central locking on her Audi and it was cured by replacing the hazard warning/ central locking switch so I have ordered one off ebay ($10) on the off chance that it will cure the problem but I am not confident.

Stan :

Hi George,
The speed-dependent locking can be deactivated by holding the the central locking switch for longer than 5 seconds when ignition is on in the unlocking mode. When button is held for closing for 5 seconds- this function is re-activated. Check what is happening when this automatic locking is deactivated. It is not likely that replacing the hazard warning switch will cure this. This function is performed by pneumatic pump module, depending on the speed signal from instrument cluster.