Possible causes

– Faulty Transmission Control Module (TCM)
– TCM harness is open or shorted
– TCM circuit poor electrical connection

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)

U0101 Description

Modules connected to the high speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

U0101 Information for specific makes

U0101 FORD
U0101 BUICK
U0101 CADILLAC
U0101 CHEVROLET
U0101 GMC
U0101 PONTIAC
U0101 SATURN