jcb JS300 Service Manual page 530

Section C - Electrics
Engine and Power Control
Engine Automatic Warm Up
increases the engine speed in 300 rpm steps at three
minute intervals up to the maximum of 1800 rpm.
After three minutes of running at 1800 rpm the engine revs
will return to the hand throttle setting.
If during the automatic warm up sequence the required
conditions change i.e. engine water temperature reaches
50 ºC or the operator selects an excavator service the
MECU will cancel the automatic warm up sequence. If the
operator selects the one touch idle function 6 or moves the
hand throttle 5 the MECU will cancel the automatic warm
up sequence
C005450GB-2
Fig 43. Example of auto warm up cycle if machine is
started at idle
C-105 9813/5100-1 C-105