Impala V8-5.3L VIN C (2006)
Information Bus: Testing and Inspection
Scan Tool Does Not Communicate with High Speed GMLAN Device
SCAN TOOL DOES NOT COMMUNICATE WITH HIGH SPEED GMLAN DEVICE
Diagnostic Fault Information
Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and Diagnostic
Overview/Diagnostic System Check - Vehicle
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/powertrain control module (ECM/PCM)
communications. The vehicle theft deterrant (VTD) module and ECM/PCM 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 connected near the data link connector (DLC) end of the link and the other is internal to the ECM/PCM, end of the link.
The DLC terminating resistor is not internal to a module.
Diagnostic Aids
-> Use the Data Link References to identify the high speed GMLAN serial data modules. See: Data Link Connector/Testing and Inspection
-> When testing for a short between the high speed GMLAN (+) and (-) circuits (ECM/PCM disconnected), a resistance reading of 120 ohms is
normal. To test for shorts to voltage or ground in the high speed GMLAN (+) and (-) circuits ensure that all modules, resistors and the scan tool
are disconnected from the buss. A normal resistance reading across the high speed GMLAN buss with the resistors, all module and scan tool
disconnected is infinite ohms.
-> This test is used for a total high speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the
vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics. See: Testing and Inspection/Diagnostic Trouble Code Tests and
Associated Procedures/U Code Charts
-> Use the DMM MIN/MAX function to capture/locate intermittent conditions.
-> 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:
- A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
- Any of the high speed GMLAN serial data circuits shorted to ground or voltage
- A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
- An inoperative BCM
Reference Information
Schematic Reference
-> Data Link Connector Schematics See: Data Link Connector/Diagrams/Electrical Diagrams
-> Control Module References See: Testing and Inspection/Programming and Relearning
Connector End View Reference
-> Master Electrical Component List See: Diagrams/Connector Views
Electrical Information Reference
-> Circuit Testing See: Testing and Inspection/Component Tests and General Diagnostics
