Scan Tool Does Not Communicate with Low Speed GMLAN Device Buss 1
Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Low Speed GMLAN Serial Data
| 1
| 2*
| 1
| --
|
Ground (DLC, terminal 5)
| --
| 1
| --
| --
|
* An open between the data link connector (DLC) and X 203, or DLC ground terminal 5 will only effect the communication with the scan tool. The vehicle modules will still communicate.
1. No communication on any low speed GMLAN module
2. No communication on a specific low speed GMLAN module
|
Circuit/System 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 when the ignition switch is in any position other than
OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses JX 300 (splice pack comb)
as a common connection between some modules and the DLC.
Diagnostic Aids
| • | Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these
can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would
most likely be attributed to one of these scenarios: |
| - | A control module on the data communication circuit was disconnected while the communication circuit is awake. |
| - | Power to one or more modules was interrupted during diagnosis |
| - | A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold. |
| - | Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time. |
| - | If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to
replace a part. |
| • | Do not replace a control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication issue. |
| • | 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. |
| • | An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed. |
| • | The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus. |
| • | Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN communications with the scan tool. |
| • | The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus. |
| | These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment
of one or more of the following concerns: |
| - | Vehicle will not crank. |
| - | Vehicle cranks but will not start. |
| - | Vehicle stability enhancement system warning lights and messages. |
| - | PRNDL gear indicator position errors. |
| - | Tire Pressure Monitor (TPM) system warning lights. |
Reference Information
Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool References
Control Module References for scan tool information.
Circuit/System Testing
- Ignition OFF, test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
| ⇒ | If greater than specified, test the ground circuit for open/high resistance. |
- Disconnect the X2 harness connector at the BCM.
- Install a 3A fused jumper wire between the BCM serial data circuit terminal 55 and the DLC terminal 1.
- Ignition ON, attempt to communicate with the BCM. Communication should be available.
Important: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not.
| ⇒ | If no communication, test the serial data circuit terminal 55 of the BCM for a short to ground, short to voltage, or an open/high resistance. If the circuit tests normal, replace the BCM. |
- Ignition OFF, install a 3A fused jumper wire between the BCM serial data circuit terminal 37 and the vehicle control interface module terminal 1.
- Disconnect the X1 harness connector at the radio, if applicable.
- Ignition ON, attempt to communicate with the theft deterrent control module (TDM), communication should not be available.
| ⇒ | If communication is established, test the radio serial data circuit terminal B10 for a short to voltage or a short to ground. If the circuit tests normal, replace the radio. |
- Ignition OFF, disconnect the X2 harness connector at the HVAC control module, if applicable.
- Ignition ON, attempt to communicate with the TDM, communication should not be available.
| ⇒ | If communication is established, test the HVAC control module serial data circuit terminal 1 for a short to voltage or a short to ground. If the circuit test normal, replace the HVAC control module. |
- Ignition OFF, disconnect the harness connector at the TDM.
- Ignition ON, attempt to communicate with the instrument panel cluster (IPC), communication should not be available.
| ⇒ | If communication is established, test the TDM serial data circuit terminal 6 for a short to voltage or a short to ground. If the circuit test normal, replace the TDM. |
- Ignition OFF, disconnect the harness connector at the IPC.
- Ignition ON, attempt to communicate with the BCM, communication should not be available.
| ⇒ | If communication is established, test the IPC serial data circuit terminal A8 for a short to voltage or a short to ground. If the circuit test normal, replace the IPC. |
- Ignition OFF, disconnect the X3 harness connector at the VCIM, if applicable.
- Ignition ON, attempt to communicate with the BCM, communication should not be available.
| ⇒ | If communication is established, test the VCIM serial data circuit terminal 7 for a short to voltage or a short to ground. If the circuit tests normal, replace the VCIM. |
- Ignition OFF, remove the 3A fused jumper wire from the BCM terminal 37.
- Ignition ON, test for less then 1 volt between the BCM serial data circuit terminal 37 and ground.
| ⇒ | If greater then the specified range, test the serial data circuit for a short to voltage. |
- Ignition OFF, test for less the 1 ohm between the BCM serial data circuit terminal 37 and ground.
| ⇒ | If greater than the specified range, test the circuit for a short to ground. |
- If all circuits test normal, replace the BCM.
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the repair.
Scan Tool Does Not Communicate with Low Speed GMLAN Device Buss 2
Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Low Speed GMLAN Serial Data
| 1
| 2*
| 1
| --
|
Ground (DLC, terminal 5)
| --
| 1
| --
| --
|
* An open between the data link connector (DLC) and X 203, or DLC ground terminal 5 will only effect the communication with the scan tool. The vehicle modules will still communicate.
- No communication on any low speed GMLAN module
- No communication on a specific low speed GMLAN module
|
Circuit/System 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 when the ignition switch is in any position other than
OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses JX 300 (splice pack comb)
as a common connection between some modules and the DLC.
Diagnostic Aids
| • | This test is used for a total low 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. |
| • | An open in the low speed GMLAN serial data circuit between the splice pack (comb) and a module(s) will only effect the specific module(s). This type of failure will set a loss of communication DTC for each module effected, and the other modules will
still communicate. |
| • | 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. |
| • | An open between the data link connector (DLC) and X 203 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start. |
| • | The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit. |
| | The following conditions may cause a total loss of low speed GMLAN data communication: |
| - | The low speed GMLAN serial data circuit shorted to ground or voltage. |
| - | A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit. |
| - | An open in the DLC ground circuit. |
| • | Use the DMM MIN/MAX function to capture/locate intermittent conditions. |
Reference Information
Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool References
Control Module References for scan tool information.
Circuit/System Testing
- Ignition OFF, test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
| ⇒ | If greater than specified, test the ground circuit for open/high resistance. |
- Disconnect the X2 harness connector at the BCM.
- Install a 3Amp fused jumper wire between the BCM serial data circuit terminal 55 and the DLC terminal 1
- Ignition ON, attempt to communicate with the BCM. Communication should be available.
Important: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not.
| ⇒ | If no communication, test the serial data circuit terminal 55 of the BCM for a short to ground, short to voltage, or an open/high resistance. If the circuit tests normal, replace the BCM. |
- Ignition OFF, disconnect the X1 harness connector at the BCM.
- Ignition OFF, install a 3 Amp fused jumper wire between the BCM serial data circuit termial 55 and the inflatable restraint sensing and diagnostic module (SDM) terminal 2.
- Disconnect the X1 harness connector at the folding top control module, if applicable.
- Ignition ON, attempt to communicate with the SDM, communication should not be avaiable.
| ⇒ | If communication is established, test the folding top control module serial data circuit terminal 2 for a short to voltage or a short to ground. If the circuit tests normal, replace the folding top control module. |
- Ignition OFF, disconnect the harness connector at the digital radio receiver (DRR), if applicable.
- Ignition ON, attempt to communicate with the SDM, communication should not be available.
| ⇒ | If communication is established, test the DRR serial data circuit terminal 5 for a short to voltage or a short to ground. If the circuit test normal, replace the DRR. |
- Ignition OFF, disconnect the harness connector at the RCDLR.
- Ignition ON, attempt to communicate with the SDM, communication should not be available.
| ⇒ | If communication is established, test the RCDLR serial data circuit terminal 2 for a short to voltage or a short to ground. If the circuit test normal, replace the RCDLR. |
- Ignition OFF, disconnect the harness connector at the SDM.
- Ignition ON, attempt to communicate with the BCM, communication should not be available.
| ⇒ | If communication is established, test the SDM serial data circuit terminal 32 for a short to voltage or a short to ground. If the circuit test normal, replace the SDM. |
- Ignition OFF, remove the 3 Amp fused jumper wire from the BCM terminal 55.
- Ignition ON, test for less then 1 volt between the BCM serial data circuit terminal 55 and ground.
| ⇒ | If greater the the specified range, test the serial data circut for a short to voltage. |
- Ignition OFF, test for less the 1 ohm between the BCM serial data circuit terminal 55 and ground.
| ⇒ | If greater than the specified range, test the circuit for a short to ground. |
- If all circuits test normal, replace the BCM.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the repair.
