If the above-mentioned problem is detected, one possible cause may be faulty software (engine control unit).
Despite programming the cruise control system to the desired cruising speed, this speed is not permanently maintained while driving.
In order to exclude other possible causes of malfunctioning, electrical and mechanical system tests (according to vehicle manufacturer specifications) and also an error code query using a suitable diagnostic unit should all be carried out.
If no errors are diagnosed and error codes are not stored in the engine control unit, a software update of the engine control unit is necessary and should be performed.
Finally a test drive should be undertaken in order to run a check on the repair work.
Please note that such repair work should only be carried out by an authorized specialist workshop and that the vehicle manufacturer's repair and maintenance instructions are to be observed!
Important safety note