Data Link Communication System: Diagnosis Saturn VUE I

Diagnostic Starting Point - Data Link Communications

Begin the diagnosis of the data link communications by performing the Diagnostic System Check for the system in which the customer concern is apparent. The Diagnostic System Check will direct you to the correct procedure within the Data Link Communications section when a communication malfunction is present.

Establish serial data communications with each controller. Read and record the DTCs from each controller. It is important to systematically approach serial data communications diagnostics. This vehicle has 2 separate data links with 3 different circuits to communicate to the various data links.

The high speed CAN link which supports real-time information between the ECM, TCM, EBCM, and BCM is accessible through 2 different keyword circuits.

1. Circuit 2960 supports communication (Keyword 2000) from the DLC to the ECM and TCM.
2. Circuit 5043 supports communication (Keyword 2000) from the DLC to the EBCM.

CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM. The ECM, TCM, EBCM, and BCM all communicate on the CAN serial data line.

The other modules communicate on the class 2 link which is configured in a ring, except for the OnStar® module. The ring configuration provides redundant communication paths, so that a single open does not prevent a serial communications malfunction.

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

The engine control module (ECM), electronic brake traction control module (EBTCM) and transmission control module (TCM) if applicable, communicate via a controller area network (CAN) serial data bus. The CAN serial data bus transmits over two wires at speeds high enough to ensure that the required real-time response is maintained. Modules connected to the CAN serial data circuits monitor communications. During normal vehicle operation, information and commands are exchanged among modules. A no communication condition may result from a short to voltage, short to ground, or short between the CAN high and low circuits.

Conditions for Running the DTC

1. Voltage supplied to the modules are in the normal voltage range.
2. The vehicle power mode requires serial communication to occur.

Conditions for Setting the DTC

A no communication condition is detected on CAN serial data circuits.

Action Taken When the DTC Sets

A module may use a default value for a parameter that it expected to receive via serial data.

Conditions for Clearing the MIL/DTC

1. A current DTC and MIL clear when the malfunction is no longer present.
2. A history DTC clears when requested by the scan tool or when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

The modules communicating on the CAN serial data circuits are wired parallel to each other. An open in the CAN circuits for one module will not affect other modules. A short to ground or short to voltage on either wire affects all modules no matter where the failure occurs.

Modules connected to the CAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about messages exchanged on the serial data circuits. The supervised and periodic messages are used by the receiving module as an availability indicator from the transmitter module. Each message contains the identification number of the transmitting module. When a message indicates availability of the transmitting module is not received, the receiving module sets a DTC Uxxxx; where xxxx is equal to the 4-digit transmitter module identification number.

The control module ID number list below provides a method for determining which module is not communicating. Modules with CAN serial data circuit malfunctions, or which loses power during the current ignition cycle, will set a Loss of Communication DTC by other modules requiring information from the failed module. The modules able to communicate will set a DTC Uxxxx indicating the module not communicating.

If any of the CAN circuits are shorted to battery voltage, ground or between them, no communication is possible on CAN serial data bus, and a DTC U0073 sets.

CAN ID

Conditions for Running the DTCs

1. Voltage supplied to the modules are in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

A receiving module did not detect the CAN serial data supervised periodic message from a transmitting module.

The module uses a default value for the missing parameter.

1. A current DTC and MIL clear when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. A poor connection at the inoperative module may cause this code to set.
2. A module that loses its connections to battery, ground or switched ignition may set this DTC.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the ID number of the module which sent the message for State of Health monitoring, Node Alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an ID number with at least one critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 is set. When more than one critical parameter does not have an ID number associated with it, the DTC will only be reported once. DTC U1000 will set as long as U1300 or U1301 do not have a current status.

The table below list the modules on the class 2 serial data circuit that will set a U1000 and should be actively communicating the previously described messages on the class 2 serial data circuit.

DTC U1000 Control Modules & ID Numbers

The ignition switch run power mode is selected.

The modules voltage supply is within normal operating value, approximately 9-16 volts.

At least one critical operating parameter has not been associated with a modules assigned ID number within about 5 seconds after beginning serial data communication.

The Service (Wrench) indicator illuminates.

The module will use default values for the missing parameters.

Conditions for Clearing the DTC

1. A current DTC will clear when all critical operating parameters for the module have been associated with an ID number, or at the end of the current ignition cycle.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

When a malfunction such as an open fuse to a module occurs while modules are communicating, a Loss of XXX Communication DTC is set as current. When the modules stop communicating, the ignition is turned OFF, the current Loss of XXX Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the ignition is turned ON, the module with the open fuse will not be learned by the other modules so U1000 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 is set. When this DTC sets, the module uses a default value for the missing parameter. A current DTC U1000 will clear when all of the critical operating parameters for the module have been associated with an identification number or when the current ignition cycle end. A history U1000 will clear upon executing 100 ignition RUN cycles with no recurrence of the malfunction.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring, Node Alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module's Node Alive message. Each module on the class 2 serial data circuit, which is powered and performing functions that require detection of a communications malfunction, is required to send a Node Alive message every 2-5 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx, where xxx is equal to the 3 digit identification number, is set.

The control module ID number list below provides a method for determining which module is not communicating. A module with a class 2 serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that can not communicate. As long as U1300 and U1301 are not set as current, DTC U1001-U1254 will set.

DTC U1001-U1254 Control Modules & ID Numbers

When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table
2. The DTC which is reported the most times
3. From the lowest number DTC to the highest number DTC

1. The vehicle power mode, ignition switch position, requires serial data communication to occur.
2. The module supply voltage is in the normal operating range of 9-16 volts.

A message from a learned identification number has not been detected for the past 5 seconds.

1. A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. An intermittent open of the class 2 serial data circuit to the inoperative module may cause this code to set.
2. A poor connection at the inoperative module may cause this code to set.
3. An intermittent open in the splice may cause this code to set.
4. An improperly powered module may cause this code to set.
5. A current DTC will clear when a Node Alive, State of Health, message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
6. A history DTC will clear after 100 engine running cycles with no recurrence of the malfunction.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition to this, Node Alive messages are transmitted by each module on the class 2 serial data circuit about once every 2-5 seconds. When the module detects one of the following conditions on the class 2 serial data circuit for approximately 3 seconds, the setting of all other class 2 serial communication DTCs is inhibited and a DTC will set.

DTC U1300, U1301, or U1305 Circuit Description

1. Voltage supplied to the module is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. These DTCs cannot be retrieved with a current status. Diagnosis of current DTCs is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to «Scan Tool Does Not Communicate with Class 2 Device»(ref-188767-S36706053912005090200000) .
2. An intermittent condition is likely to be caused by a short on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to «Scan Tool Does Not Communicate with Class 2 Device»(ref-188767-S36706053912005090200000) .

The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM), body control module (BCM), and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure the required real-time response is maintained. The CAN serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM.

Modules connected to the CAN serial data circuit monitors communication during normal vehicle operation, where operation information is exchanged among the modules. Each module on the CAN network maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255, the controller removes itself from the network and DTC U2100 will result.

1. Supply voltage to the modules are in the normal operating range.
2. The vehicle is in the RUN power mode.

The module setting the DTC has attempted to establish communications on the CAN circuits for more than 7 times.

1. The ECM turns ON the MIL during the second consecutive drive cycle with the error detected.
2. The ECM records the operating conditions at the time of turning ON the MIL and stores the data as Freeze Frame information.
3. The EBCM disables the traction control system.
4. The LED in the traction control system switch is turned OFF.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes after 3 consecutive drive cycles.
2. A current DTC clears and the MIL is turned OFF when the fault is no longer present.
3. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the fault, or after 40 consecutive drive cycles.

DTC U2100

The controller area network (CAN) serial data line is a high sped serial data bus used to communicate information between the engine control module (ECM), body control module (BCM), and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure the required real-time response is maintained. The CAN serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM. The CAN bus is continuously monitored by the modules on the serial data bus.

1. Supply voltage to the modules are in the normal operating range.
2. The ignition is cycled from OFF to RUN.

Each controller on the CAN serial data circuit monitors the activity or traffic on the bus. The module setting the DTC does not receive CAN formatted messages from all of the modules it expected to, or receives too many CAN formatted messages. This indicates that there may be fewer controllers or more controllers actively communicating on the bus than programmed. After the seventh attempt, the module sets on one of the following DTCs

1. DTC U2102 - More Controllers
2. DTC U2103 - Fewer Controllers

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) turns ON during the second consecutive drive cycles with the error detected in the ECM.
3. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
4. The ECM records the operating conditions at the time of turning ON the MIL and stores the data as Freeze Frame information.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes after 3 consecutive drive cycles.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.
4. The MIL turns OFF.

DTC U2102 or U2103

The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM), body control module (BCM), electronic brake control module (EBCM), and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The CAN serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM.

Each module on the CAN serial data circuit learns the identity of the other modules on the circuit. If a module stops communicating after all modules have initiated for the ignition cycle, other modules set a DTC specific for the module not communicating

1. DTC U2105, can not communicate with the ECM
2. DTC U2106, can not communicate with the TCM
3. DTC U2107, can not communicate with the BCM
4. DTC U2108, can not communicate with the EBCM

DTC U2105-U2199 Control Modules & ID Numbers

1. Supply voltage to the modules are in the normal operating range.
2. The vehicle is in the RUN power mode.

The module setting the DTC has attempted to establish communications on the CAN circuits more than 7 times.

Besides storing the DTC as both current and history and using default values for missing parameters, the modules on the CAN network each take separate actions as listed

1. Engine control module (ECM) Turn ON the MIL during the second consecutive drive cycle with the error detected. Record the operating conditions at the time of turning ON the MIL and store the data as Freeze Frame information.
2. Transaxle control module (TCM) Send a request to the ECM to turn ON the MIL during the second consecutive drive cycle with the error detected.
3. Electronic brake control module (EBCM) The traction control system (TCS) is disabled. Turn OFF the TCS LED in the TCS switch. The EBCM may also set C0236, C0241, C0276, when a U code is current in the EBCM.
4. Body control module (BCM) Turn ON the MIL during the second consecutive drive cycle with the error detected. Record the operating conditions at the time of turning ON the MIL and store the data as Freeze Frame information.

The MIL is cleared, turned OFF, and the DTC is cleared by a different strategy for each module.

1. ECM If the fault is not detected 3 consecutive drive cycles, the current DTC is cleared and the MIL is turned OFF. The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles. The history DTC is cleared if there is a KAM reset (battery disconnected).
2. TCM If the fault is not detected one consecutive drive cycle, the current DTC is cleared. The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
3. EBCM If the fault is not detected on consecutive drive cycle, the current DTC is cleared and the TCS LED is illuminated. The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
4. BCM If the fault is not detected 3 consecutive drive cycles, the current DTC is cleared and the MIL is turned OFF. The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles. The history DTC is cleared if there is a KAM reset (battery disconnected).

DTC U2105-U2199 Diagnostic Test

Symptoms - Data Link Communications

1. Perform the applicable diagnostic system check 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 line.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Data Link Communications Description and Operation»(ref-188767-S37677586442005090200000) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the vehicle systems. Refer to «Checking Aftermarket Accessories»(ref-188770-S05143345352005090200000) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Scan Tool Does Not Power Up»(ref-188767-S11665162092005090200000)
2. «Scan Tool Does Not Communicate with Class 2 Device»(ref-188767-S36706053912005090200000)
3. «Scan Tool Does Not Communicate with Keyword Data Line»(ref-188767-S03257158492005090200000) .

The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following

1. Scan tool power battery positive voltage at terminal 16.
2. Scan tool power ground at terminal 4.
3. Common signal ground at terminal 5.

The scan tool will power up with the ignition OFF.

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes.

The following conditions will cause a class 2 serial data communication malfunction

1. The BCM detects that the ignition switch is ON and sends the appropriate power mode message to the other modules connected to the class 2 serial data circuit. The BCM must be connected to the class 2 serial data circuit for many other modules to communicate with the scan tool.
2. A class 2 serial data circuit shorted to ground. A history U1300 will set in all modules. Refer to «DTC U1300, U1301, or U1305»(ref-188767-S21907629242005090200000) .
3. A class 2 serial data circuit shorted to voltage. A history U1301 will set in all modules. Refer to «DTC U1300, U1301, or U1305»(ref-188767-S21907629242005090200000) .
4. An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.
5. If the malfunction is intermittent check for poor connections at the suspect module. Wiggling the harness wiring may help in locating the fault.

Scan Tool Does Not Communicate with Low Speed GMLAN Device

Modules connected to the GMLAN serial data circuit monitor for serial data communications on the 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 U2100 will be set. This DTC can be retrieved as history only.

The engine will not start when there is a total malfunction of the GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of GMLAN data communication

1. Any of the serial data circuits shorted to ground.
2. Any of the serial data circuits shorted to voltage.
3. A short between serial data circuits.
4. An internal malfunction of a module on the GMLAN network that causes a short to voltage or ground.

Scan Tool Does Not Communicate with Low Speed GMLAN Device

The Keyword protocol utilizes a single wire bi-directional data line between the modules and the scan tool. The message structure is a request and response arrangement. Keyword serial data is used for scan tool diagnostics only. The modules do not exchange data on this circuit.

The following modules are connected to the Keyword serial data circuit

1. Electronic brake control module (EBCM)
2. Engine control module (ECM)
3. Transmission control module (TCM)

1. If the malfunction is intermittent, check for poor connections at the suspect module. Wiggling the harness wiring may help in locating the fault.
2. Diagnostic trouble codes (DTCs) may be set do to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Scan Tool Does Not Communicate with Keyword Data Line

Regulations and agreements among the automobile manufacturers have resulted in the data link connector (DLC). This connector must be used for the scan tool and programming access to all communications systems used for those purposes on the vehicle. The connector must have the following

1. A 16-pin connector configuration to which all scan tools connect
2. Scan tool battery power always available at pin 16
3. Scan tool ground always available at pin 4
4. A clean signal ground always available at pin 5

The rest of the pins are available for serial data communications to the vehicle system.

The serial data circuits are the means by which the microprocessor controlled modules in the vehicle communicate with each other and the scan tool. There are 4 different types of protocols on this vehicle.

1. Class 2
2. Controller area network (CAN)
3. Keyword 2000
4. GMLAN

Class 2 Data Line Circuit Description

Saturn utilizes class 2 communications system for most vehicle system controllers that must exchange data and commands. Class 2 data is pulse width modulated. The pulse width modulation of class 2 data allows better utilization of the data line.

The messages carried on class 2 data streams are also prioritized. This means if 2 devices try to communicate on the data line at the same time, only the higher priority message will continue. The device with the lower priority message must wait. The modules on the class 2 data line are

1. Body control module (BCM)
2. Power steering control module (PSCM)
3. Instrument panel cluster (IPC)
4. Inflatable restraint sensing and diagnostic module (SDM)
5. Vehicle communication interface module (VCIM), if equipped

GMLAN Low Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a single wire to the appropriate control modules. The transmission speed for GMLAN low speed is up to 83.33 Kb/s. Under normal vehicle operating conditions the speed of the buss is 33.33 Kb/s. This protocol produces a simple pules train sent out over the GMLAN low speed serial data bus. When a module pulls the buss high, 5 volts, this creates a dominant logic state or 0 on the buss. When the buss is pulled low 0 volts, it is translated as a recessive logic state or 1. To wake the control modules connected to the GMLAN low speed serial data buss a high voltage wake up pulse is sent out over the buss, the voltage level of the pules is +10 volts. Modules connected to the GMLAN low speed buss can be part of a virtual network as described in the previous paragraph. The modules on the GMLAN low speed serial data buss are connected to the buss in a parallel configuration.