Conditions for Setting the DTCs
- No valid messages are detected on the class 2 serial data circuit.
- The voltage level detected on the class 2 serial data circuit is in one of the following conditions: High Low
- The above conditions are met for approximately 3 seconds.
Action Taken When the DTCs Sets
The module uses default values for all parameters received on the class 2 serial data circuit.
Keyword Serial Data to DLC pin 12
Electronic brake control module (EBCM)
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Data Communication Schematics Connector End View Reference: Data Communication Connector End Views | |||
| 1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle |
| 2 | Connect the scan tool to the data link connector (DLC). Turn ON the ignition, with the engine OFF. Attempt to communicate with each module on the both keyword serial data circuits: Engine control module (ECM) Transmission control module (TCM) Electronic brake control module (EBCM) Does the scan tool communicate with all the modules on the keyword serial data circuit? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
| 3 | Disconnect the scan tool from the DLC. Turn OFF the ignition. Disconnect all non-communicating modules on the respective keyword serial data circuit. Turn ON the ignition, with the engine OFF. Test the respective keyword serial data circuit between the DLC and the modules on the keyword serial data circuit, for the following conditions: An open A short to ground A short to voltage Refer to the following: Circuit Testing Wiring Repairs Did you find and correct the condition? | Go to Step 9 | Go to Step 4 |
| 4 | IMPORTANT: Perform the following 2 steps if the scan tool didn't communicate with both ECM and TCM. Otherwise skip to step 6. Reconnect the TCM. Turn ON the ignition with the engine OFF. Attempt to communicate with TCM. Does the scan tool communicate with TCM? | Go to Step 5 | Go to Step 6 |
| 5 | Consider the ECM as non communicating module for the following steps. | Go to Step 6 | |
| 6 | Test the following circuits of the module that is not communicating for an open or high resistance: The battery positive voltage input circuits The battery positive voltage output circuits The ignition voltage input circuits The ignition voltage output circuits The switched battery positive voltage supply circuits The ground circuits Refer to the following: Control Module References for the applicable schematic Circuit Testing Wiring Repairs Did you find and correct the condition? | Go to Step 9 | Go to Step 7 |
| 7 | Inspect for poor connections and terminal tension at the following harness connector circuits of the module that is not communicating : The battery positive voltage input circuits The battery positive voltage output circuits The ignition voltage input circuits The ignition voltage output circuits The switched battery positive voltage supply circuits The ground circuits The Keyword serial data circuits Refer to the following: Control Module References for the applicable schematic Testing for Intermittent Conditions and Poor Connections Connector Repairs Did you find and correct the condition? | Go to Step 9 | Go to Step 8 |
| 8 | Replace the module that is not communicating on the Keyword serial data circuit. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 9 | |
| 9 | Connect all modules and connectors. Connect the scan tool to the DLC. Turn ON the ignition, with the engine OFF. Attempt to communicate with all modules on keyword serial data circuits. Does the scan tool communicate with all the modules on the keyword serial data circuits? | System OK | Go to Step 2 |
| IMPORTANT |
|---|
| Perform the following 2 steps if the scan tool didn't communicate with both ECM and TCM. Otherwise skip to step 6. |
Scan Tool Does Not Communicate with Keyword Data Line
Data Link References
This table identifies which serial data link that a particular module uses for in-vehicle data transmission and communication with the scan tool. Some modules may use more than one data link to communicate. Some modules may use different circuits for functional and diagnostic communication. Use the schematic reference link in the table for additional information. This table is used to assist in correcting a communication malfunction. For the description and operation of these serial data communication circuits refer to Data Link Communications Description and Operation .
| Control Module | Data Link Type | Diagnostic Procedure |
|---|---|---|
| Schematic Reference: Data Link Communications Description and Operation | ||
| Body Control Module (BCM) | Class 2 CAN | Scan Tool Does Not Communicate with Class 2 Device |
| Communication Interface Module (OnStar) | Class 2 | Scan Tool Does Not Communicate with Class 2 Device |
| Digital Radio Receiver | Low Speed GMLAN | Scan Tool Does Not Communicate with Low Speed GMLAN Device |
| Electronic Brake Control Module (EBCM) | Keyword Data Line CAN | Scan Tool Does Not Communicate with Keyword Data Line |
| Engine Control Module (ECM), with L61 | Keyword Data Line CAN | Scan Tool Does Not Communicate with Keyword Data Line |
| Inflatable Restraint Sensing and Diagnostic Module (SDM) | Class 2 | Scan Tool Does Not Communicate with Class 2 Device |
| Instrument Panel Cluster (IPC) | Class 2 | Scan Tool Does Not Communicate with Class 2 Device |
| Power Steering Control Module (PSCM) | Class 2 | Scan Tool Does Not Communicate with Class 2 Device |
| Powertrain Control Module (PCM), with L66 | Keyword Data Line CAN | Scan Tool Does Not Communicate with Keyword Data Line |
| Radio | Low Speed GMLAN | Scan Tool Does Not Communicate with Low Speed GMLAN Device |
| Transmission Control Module (TCM), with L61 | Keyword Data Line CAN | Scan Tool Does Not Communicate with Keyword Data Line |
Data Link References
Gateway
The body control module (BCM) communicates functionally on both class 2 and controller area network (CAN) serial data buses. The BCM is the gateway between the buses and transfers serial data messages from one subnet to another. Diagnostic communication of the BCM with the scan tool is through class 2 serial data circuit.
BCM Functions
The body control module (BCM) performs multiple body control functions. The BCM can control devices directly connected to its outputs based on input information. The BCM evaluates this information and controls certain body control systems by commanding outputs on or off. The BCM inputs can be
- Sensors and switches that are directly connected to the BCM
- Class 2 serial data messages received from other vehicle systems connected to the class 2 serial data link
- Controller area network (CAN) serial data messages received from other vehicles systems connected to the CAN serial data link
The BCM is also capable of controlling other vehicle systems that are not directly wired to the BCM. The BCM does this by sending specific messages on the class 2 serial data link or CAN serial data link. The system capable of performing the required function will respond to the BCM messages.
Some of the other systems functions that BCM controls or contributes to are
- Audible warnings-Refer to «Audible Warnings Description and Operation»(ref-269324-S07148734682007103000000)
- Exterior lighting control-Refer to «Exterior Lighting Systems Description and Operation»(ref-269288-S41070423952007103000000)
- Interior lighting-Refer to «Interior Lighting Systems Description and Operation»(ref-269288-S29645276122007103000000)
- Automatic door locks-Refer to «Power Door Locks Description and Operation»(ref-269297-S30687434642007103000000)
- Keyless entry-Refer to «Keyless Entry System Description and Operation»(ref-269318-S42060800522007103000000)
- Theft deterrent-Refer to «Content Theft Deterrent (CTD) Description and Operation»(ref-269372-S16819359492007103000000)
- Wipers/washers-Refer to «Wiper/Washer System Description and Operation»(ref-269292-S08913814232007103000000)
- Rear defogger-Refer to «Rear Window Defogger Description and Operation»(ref-269300-S05659516012007103000000)
- Horn-Refer to «Horns System Description and Operation»(ref-269317-S00985959402007103000000)
Power Mode
The BCM is the power mode master (PMM). Refer to Power Mode Description and Operation for more information.
Class 2 Serial Data Circuit
The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data line. This serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Once the scan tool is connected to the class 2 serial data line through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average, class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7.0 volts during normal operation. Each module can pull this lower during the transmission. The bus is not at battery positive voltage or ground potential during normal operation. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a state of health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set an internal DTC associated with the loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating, for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.
The class 2 serial data circuit on this vehicle consists of ring configuration. Each module on the ring has 2 class 2 serial data circuits connected to it. If there is one open on the ring serial data communication will still take place. If there is more than one open on the ring, the modules not connected to the class 2 serial data circuit will not communicate. The only exception from the ring configuration is the communication interface module (OnStar), with UE1, that is connected to splice S203. The following modules are connected to the class 2 serial data circuit in a ring fashion
- Body control module (BCM)
- Instrument panel cluster (IPC)
- Power steering control module (PSCM)
- The inflatable restraint sensing and diagnostic module (SDM)
CAN Serial Data Circuit
The controller area network (CAN) serial data line is used for functional messages only and does not communicate with the scan tool via the data link connector (DLC). The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.
The body control module (BCM) acts as gateway between CAN and class 2 serial data lines, transmitting messages from one subnet to another. The BCM emulates the CAN modules on the class 2, embedding the original transmitter ID in translated CAN messages to class 2. Therefore the class 2 modules can set specific non communications DTCs against CAN modules. This concept doesn't apply for class 2 to CAN transmitted messages. Therefore the CAN modules consider the BCM as being the originator of all class 2 messages that they receive. The following modules communicate on the CAN serial data line
- Electronic brake control module (EBCM)
- Transmission control module (TCM), w/L61
- Engine/powertrain control module (ECM/PCM)
Low Speed GMLAN Serial Data Circuit
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 low speed GMLAN is up to 83.33 Kbps. This high speed is used for programming purposes only. Under normal vehicle operating conditions the speed of the bus is 33.33 Kbps. This protocol produces a simple pulse train sent out over the low speed GMLAN serial data bus. To wake up the control modules connected to the low speed GMLAN serial data bus, a wake-up pulse of 10 volts is sent out over the bus.
The modules on the low speed GMLAN serial data line are
- Radio, w/U32
- Digital radio receiver (DRR), w/U2K
Keyword 2000 Serial Data Circuit
The Keyword protocols 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 2000 is used for scan tool diagnostics only. The modules do not exchange data on these systems. They are two independent Keyword serial data circuits connected to data link connector (DLC) terminals 7 and 12. The following modules communicate with scan tool through Keyword 2000 serial data circuits
Keyword serial data to DLC terminal 7
- Transmission control module (TCM), w/L61
- Engine control module (ECM)/powertrain control module (PCM)
Keyword serial data to DLC terminal 12
Electronic brake control module (EBCM)