Scan Tool Does Not Communicate with Low Speed GMLAN Device. Cadillac STS 2006

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 2006 🢒 STS 🢒 Vehicle Control Systems 🢒 Computer/Integrating Systems 🢒 Scan Tool Does Not Communicate with Low Speed GMLAN Device

Circuit Description

Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

A current DTC U2100 71 or U2100 00 may be retrieved only from instrument panel module (IPM).

A partial malfunction in the low speed GMLAN serial data circuit uses a different procedure from a total malfunction of the low speed GMLAN serial data circuit. The scan tool communicates with the following modules on the low speed GMLAN serial data circuit:

•	Audio amplifier

•	Communication interface module (OnStar)

•	Digital radio receiver (DRR)

•	Driver door module (DDM)

•	Driver door switch (DDS)

•	Driver position module (DPM)

•	Head up display (HUD)

•	HVAC control module

•	Inflatable restraint sensing and diagnostic module (SDM)

•	Instrument panel cluster (IPC)

•	Left rear door module (LRDM)

•	Passenger door module (PDM)

•

Radio

•	Rear integration module (RIM)

•	Remote control door lock receiver (RCDLR)

•	Right rear door module (RRDM)

•	Steering column lock control module (SCLCM)

•	Television module

An open in the low speed GMLAN serial data circuit between the DLC and instrument panel module (IPM) will prevent the scan tool from communicating with any module on the low speed GMLAN bus. This condition will not set a DTC.

Step	Action	Yes	No
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List
1	Did you perform the Diagnostic System Check - Vehicle?	Go to Step 2	Go to Diagnostic System Check - Vehicle
2	Important: Make sure the CANdi module works fine. When functioning properly, CANdi's LED flashes. In the event of a problem, the LED will be constantly illuminated. Refer to the Test Description for the list of modules that communicate with scan tool on low speed GMLAN bus. Did the scan tool communicate with any module on the low speed GMLAN serial data circuit?	Go to Step 5	Go to Step 3
3	Does the scan tool communicate with instrument panel module (IPM)?	Go to Step 4	Go to Scan Tool Does Not Communicate with High Speed GMLAN Device
4	Did you retrieve DTC U2100 71 and/or U2100 00 set as current?	Go to DTC U2100	Go to Step 7
5	Did you record any DTCs in the range of U2100 to U2199?	Go to DTC U2105-U2199	Go to Step 6
6	Diagnose the non-communicating module by using the DTC U2100-U2199 procedure for the module which is not communicating. Refer to DTC U2105-U2199 . Did you complete the action?	Go to Diagnostic System Check - Vehicle	--
7	Turn OFF the ignition. Disconnect the scan tool from the data link connector (DLC). Inspect for poor connections at the DLC terminals 1 and 5. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	Go to Diagnostic System Check - Vehicle	Go to Step 8
8	Test the DLC ground circuit at terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	Go to Diagnostic System Check - Vehicle	Go to Step 9
9	Disconnect the instrument panel module (IPM). Inspect for poor connections at the low speed GMLAN serial data circuits of the IPM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	Go to Diagnostic System Check - Vehicle	Go to Step 10
10	Repair the low speed GMLAN serial data circuit between the DLC and the IPM for an open. Refer to Circuit Testing and GMLAN Wiring Repairs . Did you complete the action?	System OK	--