Sky L4-2.4L (2007)
Information Bus: Symptom Related Diagnostic Procedures
Symptoms - Computer/Integrating Systems
Symptoms - Computer/Integrating Systems
Important: The following steps must be completed before using the symptom tables.
1. Perform the Diagnostic System Check - Vehicle before using the symptom tables in order to verify that all of the following are true:
* There are no DTCs set.
* The control modules can communicate via the serial data links. See: Testing and Inspection/Initial Inspection and Diagnostic
Overview/Diagnostic System Check - Vehicle
2. Review the system operation in order to familiarize yourself with the system functions. Refer to:
* Data Link Communications Description and Operation
* Body Control System Description and Operation
Visual/Physical Inspection
* Inspect for aftermarket devices which could affect the operation of the systems. Refer to Checking Aftermarket Accessories. See: Testing and
Inspection/Component Tests and General Diagnostics
* Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
Intermittent
Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections.
See: Testing and Inspection/Component Tests and General Diagnostics
Symptom List
Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom:
* Scan Tool Does Not Power Up
* Scan Tool Does Not Communicate with High Speed GMLAN Device
* Scan Tool Does Not Communicate with Low Speed GMLAN Device
Scan Tool Does Not Communicate with High Speed GMLAN Device
Scan Tool Does Not Communicate with High Speed GMLAN Device
Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications on the high speed GMLAN network during
normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC
U0001 or U2100 will be set. These DTCs can be retrieved as history only.
Diagnostic Aids
The high speed GMLAN serial data buss uses two 120 ohms terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits.
One of the resistors is connected at the data link connector (DLC) end of the link and the other is at the engine management module, engine control
module (ECM) or powertrain control module (PCM), end of the link. The DLC terminating resistor resides internally in the BCM. When testing for a
short between high speed GMLAN (+) and (-) with the engine management module removed, a reading off 120 ohms is normal. However, to completely
analyze the buss the body control module (BCM) should be temporally removed when testing for shorts between the high speed GMLAN (+) and (-)
while also making sure that all modules and the scan tool are disconnected from the buss. A normal reading across the high speed GMLAN buss with the
terminating resistor at the DLC remove and all module and scan tool disconnected is infinite ohms. Make certain to reconnect the BCM after testing, it is
necessary for proper vehicle powermoding.
The engine will not start when there is a total malfunction of the high speed GMLAN serial data circuits while the engine is not running. 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
