W126 power lock gremlin - motor in boot won't stop cycling!

[kraz]

Hello all:

My 1984 500 SEL W126 has a new problem with the power locks, which previously worked fine. The small motor which lives in the spare wheel well in the boot continuously cycles. Click, whir, click, whir...

I'm not sure if this is a compressor or a vacuum pump, but I assume it powers the locks in the four doors and boot lid up and down.

Question: is this likely to be a failure of a triggering switches in the driver's door lock or boot lock, or in the unit itself? Or somewhere else?

Any other suggestions for how to tackle this new and exciting electrical failure? For the moment I have disabled the motor by removing the 3-pin electrical connector.

Thanks in advance for any tips!

 

[Andy]

W126 power lock gremlin

Hi Jef,

The first thing you need to acertain is is there a leak. Check the petrol flap cell first, its fairly easy to get to, but you may need to check them all to acertain which is causing the motor to work all the time.

To answer your question about is it a compressor or vacuum pump. Well its both. As it sucks when you lock and blows when you open.  The central locking lines are easier to diagnose than the earlier 116 models as there is only one line around the vehicle.

Hope I've been some help.

Regards

Andy @ www.mercedesservicing.com

 

[kraz]

W126 power lock gremlin

SO then...

This type of malfunction can only be caused by a leak, not an electrical/electronic problem?

It seems to me that if there was a leak, the locks wouldn't go up and down...Moreover, when the pump is cycling endlessly, if the locks are down, and you try to raise the passenger door lock with the key, you must fight the very strong suction to keep the lock open. That doesn't feel like a leak either.

I think the question is what tells the pump to stop blowing or sucking at the end of a locking or unlocking operation: is it the position of the master lock, or is there some sort of logic chip?

I assume to check the individual cells, you pull off   the boot lining and the door panels. Can a leak be heard, or do you have to execute a test?

Thanks for any additional information which would help me diagnose the problem.

Regards,

Jeff in Boston

 

[Andy]

W126 power lock gremlin

Hi

If your saying there is no leak. Then it is more than likely the pump. The front door switches and boot lock tell it when to open & close. You could try disconnecting it for 10 mins or so and see if it resets itself.

Regards

Andy @ www.mercedesservicing.com