alarm fault please help

[beermonsterblack]

hi my 1990 gsi has a alarm fault (factory fitted) basicly it keeps sounding forno reason so I read the codes and had 29 and 38

29 Ultrasonic sensor passenger side - open circuit or incorrect voltage
38 Ultrasonic's caused an alarm condition

so I replaced the sensors and all seemed well for a good 4 hours then at midnight off she went again so rechecked the codes and I know only get
38 Ultrasonic's caused an alarm condition
does anyone have any ideas coz it is doing my head in just as a side note sometimes when I lock the car the locks go mad up down up down and sometimes when I unlock the car the lock turns but nothing happens after about 3 goes it will unlock

[btcctroy]

Faulty central locking module.
Or ingress of moisture

[beermonsterblack]

is that the little black box in drivers kick panel

[humbucker]

Yup. It has "Klikert" or similar printed on it.

[beermonsterblack]

ok thanks guys would that cause the code 38