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| • | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Refer to Control Module U Code List .
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Low Speed GMLAN Serial Data | 1 | U2105-U2199 | 1 | -- |
Battery Positive Voltage Circuits | U2105-U2199 | U2105-U2199 | -- | -- |
Ignition Voltage Circuits | U2105-U2199 | U2105-U2199 | -- | -- |
Module Ground Circuits | U2105-U2199 | U2105-U2199 | -- | -- |
Accessory Wake Up Serial Data | U1814 | U2105-U2199 | -- | -- |
High Speed GMLAN Serial Data Wake Up | U2099 | U2105-U2199 | -- | -- |
1. Scan tool does not communicate with low speed GMLAN device | ||||
Control modules connected to the high and low speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the control modules. The control modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
The body control module (BCM) activates the high speed GMLAN serial data wake up and the accessory wake up serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The high speed GMLAN serial data wake up circuit wakes up the electronic brake control module (EBCM) for bus communication and the accessory wake up serial data circuit wakes up the engine control module (ECM) and transmission control module (TCM).
| • | The system voltage is between 9-16 volts. |
| • | The vehicle power mode requires serial data communication to occur. |
A supervised periodic message that includes the transmitter module availability has not been received.
The control module uses a default value for the missing parameters.
| • | A current DTC clears when the malfunction is no longer present. |
| • | A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction. |
| • | Use the DTC Descriptor list above to determine the module which is not communicating. |
| • | If there are multiple non-communicating modules choose the one closest to the data link connector (DLC). |
| • | Use Data Link References to determine if the control module uses high or low speed GMLAN serial data communications |
| • | Some control modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no control module output voltage circuit is shorted to ground before replacing the control module. |
| • | This diagnostic can be used for any control module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that control module. |
Data Link Communications Description and Operation
Control Module References for scan tool information
Note: If more than one control module is not communicating use Data Communication Schematics to determine which control module is closest to the DLC. Start diagnostics with that control module.
Terminal and connector identifiers will be different depending on the individual control module being tested. Use Schematic Reference and Connector End View Reference to determine which connector and terminal to access.| ⇒ | If greater than specified range, test the ground circuit for an open/high resistance. |
Note: Only the high speed GMLAN modules have a wired serial data wake up circuit. Refer to the module schematics to identify which control modules have a wake up circuit. If the control module that is not communicating does not have a serial data wake up circuit, proceed to step 5.
| ⇒ | If the test lamp does not illuminate, test the wake up circuit for an open/high resistance. If the circuits test normal, replace the K9 body control module (BCM). |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the control module for a short to ground. If the circuits test normal, replace the appropriate control module. |
| ⇒ | If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the control module for a short to ground. If the circuits test normal, replace the appropriate control module. |
| ⇒ | If greater than specified range, test the GMLAN serial data circuit for open/high resistance. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
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