Faulty central locking control unit

[hawaiian Floyd]

Hi,

Had my 1998 Passat 1.8T (44,000 miles) in the garage for a service and MOT. Asked the mechanic to check out a central locking fault I have. Key fob only opens the boot.

If I open the driver door with the key it opens ok - non of the other doors unlock. I can also unlock the passenger door with the key. Same with locking, if I use the key to lock the driver door, only that door locks.

Just had the car in for a service and MOT and asked the mechanic to check out the central locking problem. He found about 4mm of water under the carpet in the passenger footwell. Wiring looms were wet and also bottom of the Central locking control unit (located in a black box). Mechanic reckons I need a new Control unit and quoted £170 + VAT.

Read some very useful threads about diagnozing were the leak came from - very usefeul but I would like some advise on the central locking control unit as I'm not sure if I need a new one.

I removed the unit and it was quite dry inside bar from the WD40 I think the mechanic has sprayed into it. Few of the contacts had a sort of powdery blue deposit on the which I've cleaned up.

I've connected the unit back up and tested. I can hear the relay going in the control unit when I press the key fob to lock the doors. The boot locks ok but none of the doors. I can actually hear the lock mechanism working in 3 of the doors (the 4th door does actually need a new lock and had done for a while) but the doors dont actually lock.

Any advice welcome as I dont want to sped over £200 on a unit that isn't faulty.

Many thank.

[gresty]

Check wiring to ccm. Possible that a few of the splices in the loom have corroded and this can cause the fault.

[hawaiian Floyd]

Check wiring to ccm. Possible that a few of the splices in the loom have corroded and this can cause the fault.

Hi,

Thanks for your reply. Could well be as you describe above but I can actually hear the lock mechanism trying to work in all of the doors (bar the knackered one). It's almost as if it hasn't got enough oommph for want of a better word to actually open / close the lock.

Not sure if it's electrical or pneaumatic on a '98 passat.

[hawaiian Floyd]

Check wiring to ccm. Possible that a few of the splices in the loom have corroded and this can cause the fault.

Many thanks, you were spot on. Also had a bad earth too.

Central locking now working without having to fork out for a new ccm. Carpets dried out, drains under the battery unblocked and seal fixed.