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Low Speed GMLAN Circuit Description

WARNING: This page is about a different car, the 2017 Cadillac ATS. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Low Speed GMLAN Block Diagram
GM3631344Courtesy of GENERAL MOTORS COMPANY
Callout Component Name
IO6 RADIO: INFOTAINMENT SYSTEM - UPLEVEL HMI, ENHANCED CONNECTIVITY, EMBEDDED NAVIGATION
UE1 COMMUNICATION SYSTEM: VEHICLE, ONSTAR
V2S TRAILER PROVISIONS: WIRING HARNESS
UGN COLL IMMINENT BRK: VEHICLE FORWARD MOVEMENT, BRAKE PREFILL and INTELLIGENT BRAKE ASSIST
UVZ SENSOR: COLLISION AVOIDANCE and MITIGATION, VEHICLE REVERSE MOVEMENT
A45 MEMORY: SEAT ADJUSTER, MIRROR, POWER, DRIVER, PERSONALIZATION
UD5 PARK ASSIST: FRONT AND REAR
UD7 PARK ASSIST: REAR
UFT SIDE ACTIVE SAFETY: OBSTACLE DETECTION
ULS STEERING COLUMN LOCK: MECHANICAL
UFL LANE ACTIVE SAFETY: DEPARTURE WARNING
UGN COLL IMMINENT BRK: VEHICLE FORWARD MOVEMENT, BRAKE PREFILL and INTELLIGENT BRAKE ASSIST
K31 K31 Navigation Control Module
K73 K73 Telematics Communication Interface Control Module
K68 K68 Trailer Lighting Control Module
K9 K9 Body Control Module
K84 K84 Keyless Entry Control Module
T3 T3 Audio Amplifier
K124 Active Safety Control Module
K40D K40D Seat Memory Control Module - Driver
K85 Passenger Presence Module
K41 K41 Front and Rear Parking Assist Control Module
B94L B94L Side Object Sensor - Left
X84 X84 Data Link Connector
P16 P16 Instrument Cluster
K33 K33 HVAC Control Module
K109 K109 Frontview Camera Module
A11 A11 Radio
P17 P17 Info Display Module
K60 K60 Steering Column Lock Module
K36 K36 Inflatable Restraint Sensing and Diagnostic Module
B218R B218R Side Object Sensor Module - Right

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.