Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Battery Positive Voltage (B+)
| 1
| 1
| --
| --
|
Ground (DLC, Terminal 5)
| --
| 1
| --
| --
|
High Speed GMLAN Serial Data (+)
| 1
| 2*
| 1
| --
|
High Speed GMLAN Serial Data (-)
| 1
| 2*
| 1
| --
|
* An open between the data link connector (DLC) and the first splice will only effect the communication with the scan tool. The vehicle modules will still communicate.
1. No communication on any high speed GMLAN module
2. An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules
|
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 buses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial data bus 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 cargo area and the other is internal to the ECM.
Diagnostic Aids
| • | 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. |
| • | This test is used for a total high speed GMLAN communication malfunction. 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. |
| • | Some 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 module output
voltage circuit is shorted to ground before replacing the module. |
| • | An open in the data link connector (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. |
| • | 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 |
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 Reference
Control Module References
for scan tool information
Circuit/System Verification
Attempt to communicate with all modules on the high speed GMLAN bus.
| ⇒ | If any high speed module communicates and no DTC beginning with a U exists, refer to
DTC U0100-U0299
for diagnostics. |
Circuit/System Testing
High Speed GMLAN Initial Test
- Test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
- Disconnect the X200 inline harness connector at the DLC.
- Ignition ON, attempt to communicate with the fuel system control module.
| ⇒ | If communication is established refer to DIAGNOSTIC 2. |
| ⇒ | If communication is not established, refer to DIAGNOSTIC 1. |
DIAGNOSTIC 1
- Connect the X200 inline harness connector.
- Remove the 120 ohm terminator resistor.
- Test for 108-132 ohms between terminals A and B of the terminator resistor.
| ⇒ | If not within the specified range, replace the resistor. |
- Connect the harness connector at the terminator resistor.
- Ignition OFF, disconnect the X3 harness connector at the BCM.
- Ignition OFF, test for less than 2 ohms between the DLC serial data circuit terminal 6 and BCM serial data circuit terminal 8.
| ⇒ | If greater than the specified range, test the serial data circuit for open/high resistance. |
- Ignition OFF, disconnect the X2 and X4 harness connectors at the BCM.
- Test for less than 5 ohms between the following ground circuit terminals and ground.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
- Ignition ON, verify a test lamp illuminates between the following B+ circuit terminals and ground.
| ⇒ | 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 B+ output circuits for a short to ground. |
- Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
| ⇒ | If less than the specified value, test the serial data circuits for a short to ground. |
- Ignition ON, test for less than 1 volt between the following serial data circuits of the DLC and ground.
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. |
- Ignition OFF, test for infinite resistance between the DLC serial data circuit terminal 6 and terminal 14.
| ⇒ | If less than the specified value, test for a short between the serial data circuits. |
- Connect the X2, X3 and X4 harness connector at the BCM.
- Ignition OFF, disconnect the harness connector at the rear differential clutch control module.
- Ignition ON, attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If communication is established, replace the rear differential clutch control module. |
- Ignition OFF, disconnect the harness connector at the terminator resistor.
- Ignition ON, attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If communication is established, replace the terminator resistor. |
- Ignition OFF, disconnect the harness connector at the fuel system control module.
- Ignition ON, attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If communication is established, remove the terminator resistor and test the following serial data circuits between the fuel system control module and the terminator resistor or the fuel system control module and the rear differential clutch control
module for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the fuel system control module. |
| • | Fuel system control module terminal 21 |
| • | Fuel system control module terminal 22 |
| • | Fuel system control module terminal 21 and 22 |
| • | Terminator resistor terminal A |
| • | Terminator resistor terminal B |
| • | Terminator resistor terminal A and B |
- Ignition OFF, disconnect the X1 and X2 harness connector of the vehicle communication interface module (VCIM).
- Ignition ON, attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If communication is established, test the following serial data circuits between the VCIM and the ESC module for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the VCIM. |
- Ignition OFF, disconnect the X1 harness connector at the electronic power steering (EPS) module
- Ignition ON, attempt to communicate with the EBCM. Communication should not be available.
| ⇒ | If communication is established, test the following serial data circuits between the EPS module and the VCIM for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the VCIM. |
- Ignition OFF, disconnect the X3 harness connector at the BCM.
- Ignition OFF, test for infinite resistance between the following serial data circuits and ground.
| ⇒ | If less than the specified value, test the serial data circuit for a short to ground. |
- Ignition ON, test for less than 1 volt between the following serial data circuits and ground.
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. |
- Ignition OFF, test for infinite resistance between the serial data circuit terminal 16 and terminal 17.
| ⇒ | If less than the specified value, test for a short between the serial data circuits. |
- If the circuits test normal, replace the BCM.
DIAGNOSTIC 2
- Connect the X200 inline harness connector.
- Ignition OFF, disconnect the appropriate harness connector listed below at the ECM.
- Ignition ON, attempt to communicate with the EPS module. Communication should not be available.
| ⇒ | If communication is established, replace the ECM. |
- Ignition OFF, disconnect the harness connector at the TCM if applicable.
- Ignition ON, attempt to communicate with the EPS module. Communication should not be available.
| ⇒ | If communication is established, test the following serial data circuits between the ECM and the TCM for a short between the serial data circuits, short to ground or a short to voltage. If the circuits test normal replace the TCM. |
| • | RPO MH2 or MH4 - terminal 2 |
| • | RPO MH2 or MH4 - terminal 12 |
| • | RPO MH2 or MH4 - terminal 2 and 12 |
| • | RPO MN5 - terminal 37 and 38 |
| • | RPO ME7 - terminal 6 and 7 |
- Ignition OFF, disconnect the harness connector at the EBCM.
- Ignition ON, attempt to communicate with the EPS module. Communication should not be available.
| ⇒ | If communication is established, test the following serial data circuits between the EBCM and the TCM for a short between the serial data circuits, short to ground or a short to voltage. If the circuits test normal, replace the EBCM. |
- Ignition OFF, test for infinite resistance between the following serial data circuits of EBCM and ground.
| ⇒ | If less than the specified value, test the serial data circuit for a short to ground. |
- Ignition ON, test for less than 1 volt between the following serial data circuits of EBCM and ground.
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage. |
- Ignition OFF, test for infinite resistance between the serial data circuit terminal 11 and terminal 14.
| ⇒ | If less than the specified value, test for a short between the serial data circuits. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Diagnostic Instructions
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
High Speed GMLAN Serial Data (+)
| 1
| U0100-U0299*
| 1
| --
|
High Speed GMLAN Serial Data (-)
| 1
| U0100-U0299*
| 1
| --
|
Ground (DLC, terminal 5)
| --
| 1
| --
| --
|
* No communications with one or more high speed GMLAN modules. An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules. An open between the data link connector (DLC) and the first splice will only effect
the communication with the scan tool. The vehicle modules will still communicate.
1. No communication with any high speed GMLAN module
|
Circuit/System Description
The serial data is transmitted on two twisted wires that allow speeds up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the engine control module (ECM) and the other can be a separate resistor in a connector
assembly or in another control module. The resistors are used as the load for the High Speed GMLAN buss during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-)
are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) circuit and subtracts one volt from the high speed GMLAN serial data bus (-) circuit.
If serial data is lost, control modules will set a no communication code against the non-communicating control module. Note that a loss of serial data DTC does not represent a failure of the module that set it.
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 Reference
Control Module References for scan tool information
Circuit/System Testing
Note: Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:
| • | Control modules the vehicle is equipped with |
| • | High speed GMLAN serial data circuit terminating resistors |
| • | Control module locations on the high speed GMLAN serial data circuits |
| • | Each control module's high speed GMLAN serial data circuit terminals |
- Attempt to communicate with all control modules on the high speed GMLAN serial data circuit, refer to
Data Link References. Communications should not be available with two or more control modules on the
high speed GMLAN serial data circuit.
| ⇒ | If only one control module is not communicating, diagnose that control module only; refer to
DTC U0100-U0299. |
- Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
- All access doors closed, ignition OFF for 60 seconds, test for less than 10 Ω between the ground circuit terminal 5 and ground.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
- Ignition ON, test for less than 4.5 V between the serial data circuits listed below and ground:
| ⇒ | If greater than the specified range, test the serial data circuit for a short to voltage; refer to Testing the Serial Data Circuits for a Short to Voltage. |
- Ignition OFF for 60 seconds, test for greater than 100 Ω between the serial data circuits listed below and ground:
| ⇒ | If not the specified value, test the serial data circuit for a short to ground; refer to Testing the Serial Data Circuits for a Short to ground. |
- Test for 50-70 Ω between the serial data circuits terminal 6 and terminal 14.
| ⇒ | If less than 35 Ω, test for a short between the serial data circuits; refer to Testing the Serial Data Circuits for a Short between the Circuits. |
| ⇒ | If 35-50 Ω there may be a third terminating resistor between the serial data circuits. This can happen if the incorrect control module is installed. Some control modules are available with and without the terminating resistors installed
to reduce the need of terminating resistors in the wiring harness. |
| ⇒ | If greater than 70 Ω but less than infinite, test the serial data circuit for an open/high resistance; refer to Testing the Serial Data Circuits for an Open/High Resistance. |
| ⇒ | If infinite, test the serial data circuits between the DLC and the first connection to the serial data circuit for an open/high resistance. |
Testing the Serial Data Circuits for a Short to Voltage
- Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module.
- Ignition ON, test for greater than 4.5 V between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V.
| ⇒ | If all serial data circuits are less than the specified range, replace the control module that was disconnected. |
- Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to voltage.
- Ignition ON, test for greater than 4.5 V between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V.
| ⇒ | If all serial data circuits are less than the specified range, replace the control module that was just disconnected. |
- Repeat step 3 until one of the follow conditions are isolated:
| • | A short to voltage on the serial data circuit between 2 control modules |
| • | A short to voltage on the serial data circuit between a control module and a terminating resistor. |
Testing the Serial Data Circuits for a Short to Ground
- Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module.
- Ignition OFF for 60 seconds, test for less than 1k Ω between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k Ω.
| ⇒ | If all serial data circuits are greater than the specified range, replace the control module that was disconnected. |
- Disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to ground.
- Ignition OFF for 60 seconds, test for less than 1k Ω between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k Ω.
| ⇒ | If greater than the specified range for all serial data circuits, replace the control module that was just disconnected. |
- Repeat step 3 until one of the follow conditions are isolated:
| • | A short to ground on the serial data circuit between 2 control modules |
| • | A short to ground on the serial data circuit between a control module and a terminating resistor. |
Testing the Serial Data Circuits for a Short between the Circuits
- Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
- Ignition OFF for 60 seconds, test for less than 35 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 35 Ω.
| ⇒ | If each pair of serial data circuits is greater than the specified range, replace the control module that was disconnected. |
- Connect the harness connectors at the control module that was disconnected.
- Disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the circuits shorted together.
- Ignition OFF for 60 seconds, test for less than 35 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 35 Ω.
| ⇒ | If each pair of serial data circuits is within the specified range, replace the control module that was just disconnected. |
- Repeat step 3 until one of the following conditions are isolated:
| • | Serial data circuits shorted together between 2 control modules |
| • | Serial data circuits shorted together between a control module and a terminating resistor |
| • | A shorted terminating resistor |
Testing the Serial Data Circuits for an Open/High Resistance
- Ignition OFF, disconnect the harness connectors with the high speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
- Ignition OFF for 60 seconds, test for greater than 100k Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 100k Ω.
| ⇒ | If each pair of serial data circuits is less than the specified range, replace the control module that was disconnected. |
- Connect the harness connectors at the control module that was disconnected.
- Disconnect the harness connectors with the high speed GMLAN serial data circuits at another control module, in the direction of the open circuit.
- Ignition OFF for 60 seconds, test for greater than 100k Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 100k Ω.
| ⇒ | If each pair of serial data circuits is less than the specified range, replace the control module that was just disconnected. |
- Repeat step 3 until one of the following conditions are isolated:
| • | An open/high resistance on the serial data circuit between 2 control modules |
| • | An open/high resistance on the serial data circuit between a control module and a terminating resistor |
| • | An open/high resistance terminating resistor |
Repair Instructions
Perform the
Diagnostic Repair Verification after completing the repair.
