The D156 error on 39x trucks applies to display problems.
it may be:
Connector 6x1 - defect
Connector X15 - defect
The whole display defect.
If the error occures, you should have the following LEDS on:
H1 (Oil temperature)
H4 (Electric circuit problem)
H5 (Engine tempertaure)
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.