Savana 2500 V8-6.6L DSL Turbo (2008)
Circuit/System Description
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating
information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The high speed GMLAN serial
data circuits must be operational for the vehicle to start due to body control module (BCM) and engine control module (ECM) communications. The
vehicle theft deterrent (VTD) module and ECM exchange information using the BCM as the gateway module allowing communication between the high
and low speed serial data busses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial
data buss uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is in the rear
fuse block and the other is internal to the ECM.
Diagnostic Aids
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Communication may be available between the BCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition
is due to the BCM using both the high and low speed GMLAN systems.
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Use the Data Link References to identify the high speed GMLAN serial data modules.
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This test is used for a total high speed GMLAN communication failure. If only one module is not communicating and sets no DTC, ensure that the
vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
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An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with
the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module
detected" and will not communicate.
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The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
The following conditions may cause a total loss of high speed GMLAN data communication:
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A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
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Any of the high speed GMLAN serial data circuits shorted to ground or voltage
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A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
Circuit/System Verification
Attempt to communicate with all modules on the high speed GMLAN bus.
If any high speed module communicates and any DTC beginning with a U exists, refer to Diagnostic Trouble Code (DTC) List - Vehicle. See: Testing
and Inspection/Diagnostic Trouble Code Descriptions
If any high speed module communicates and no DTC beginning with a U exists, refer to DTC U0100-U0299. See: Testing and Inspection/Diagnostic
Trouble Code Tests and Associated Procedures/U Code Charts/U0100
Circuit/System Testing
High Speed GMLAN Initial Test
1. Test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
‹› If greater than the specified range, test the ground circuit for open/high resistance.
2. Ignition OFF, disconnect the harness connector (splice pack comb) at JX250.
3. Install 3 amp fused jumper wires between the following JX 250 terminals.
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Terminal K and terminal A
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Terminal C and terminal M
4. Attempt to communicate with the BCM.
5. If communication is established refer to DIAGNOSTIC 1.
6. If communication is not established, refer to DIAGNOSTIC 2.
Diagnostic 1
1. Ignition OFF, test for 108-132 ohms between terminals B and L of JX250.
‹› If greater than the specified range, test the serial data circuits between the ECM and JX250 for an open/high resistance. If the circuits test
normal, replace the ECM.
‹› If less than the specified range, test the serial data circuits between the ECM and JX250 for a short together. If the circuits test normal, replace
the ECM.
2. Verify a test lamp does not illuminate between B+ and the following JX250 terminals.