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Low Speed GMLAN Circuit Description

WARNING: This page is about a different car, the 2015 Buick LaCrosse. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Low Speed GMLAN Block Diagram
GM3635791Courtesy of GENERAL MOTORS COMPANY
Callout Component Name
UQS SPEAKER SYSTEM: PREMIUM AUDIO BRANDED WITH SURROUND AMPLIFIER
UEU SENSOR INDICATOR: FORWARD COLLISION ALERT
UFL LANE ACTIVE SAFETY: DEPARTURE WARNING
UD7 PARK ASSIST: REAR
BTM SWITCH: ENGINE START, KEYLESS
ATH LOCK CONTROL, ENTRY: REMOTE ENTRY, EXTENDED RANGE, PASSIVE ENTRY, ALL DOORS
CW1 COUNTRY: KOREA
CZ2 COUNTRY: CHINA
UFG SENSOR INDICATOR: REAR CROSS TRAFFIC ALERT
UFT SIDE ACTIVE SAFETY: OBSTACLE DETECTION
A45 MEMORY: SEAT ADJUSTER, MIRROR, POWER, DRIVER, PERSONALIZATION
KA1 HEATER SEAT FRT: DRVR and PASS
UE1 COMMUNICATION SYSTEM: VEHICLE, ONSTAR
UWG ENTERTAINMENT PKG: RR SEAT, DUAL DISPLAY, REM CONTROL, AUX JACK, 2 WIRELESS DUAL CHANNEL HEADPHONES
UWJ ENTERTAINMENT PKG: RR SEAT, DUAL DISPLAY, REM CONTROL, AUX JACK
T3 T3 Audio Amplifier
K109 K109 Frontview Camera Module
K41R K41R Rear Parking Assist Control Module
K84 K84 Keyless Entry Control Module
K85 K85 Passenger Presence Module
A13 A13 Rear Audio Control Module
B218L B218L Side Object Sensor Module - Left
K40 K40 Seat Memory Control Module
K73 K73 Telematics Communication Interface Control Module
X84 X84 Data Link Connector
S136 S136 Infotainment Control Touchpad
K33 K33 HVAC Control Module
A11 A11 Radio
P16 P16 Instrument Cluster
P17 P17 Info Display Module
A26 A26 HVAC Controls
K9 K9 Body Control Module
A33 A33 Media Disc Player
K36 K36 Inflatable Restraint Sensing and Diagnostic Module

Low Speed GMLAN Bus is used in applications where a high data rate is not required which allows for the use of less complex components. It is typically used for operator controlled functions where the response time requirements are slower than those required for dynamic vehicle control.

The Low Speed GMLAN Serial Data Network consists of a single wire, ground referenced bus with high side voltage drive. During on road vehicle operation data symbols (1's and 0's) are transmitted sequentially at the normal rate of 33.3 Kbit/s. For component programming only, a special high speed data mode of 83.3 Kbit/s may be used.

Unlike the high speed dual wire networks, the single wire low speed network does not use terminating resistors at either end of the network.

The data symbols to be transmitted over the bus are represented by different voltage signals on the bus. When the Low Speed GMLAN Bus is at rest and is not being driven, there is a low signal voltage of approximately 0.2 V. This represents a logic "1". When a logic "0" is to be transmitted, the signal voltage is driven higher to around 4.0 V or higher.