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 data link connector (DLC) allows communication with the modules for diagnostic purposes.
The engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication:
• | A class 2 serial data circuit shorted to ground |
• | A class 2 serial data circuit shorted to voltage |
• | 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 |
The numbers below refer to the step numbers on the diagnostic table.
A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit:
• | Audio Amplifier, w/UQ7 and Y91 |
• | Body Control Module (BCM) |
• | CD Changer (CDX), w/U1S and Y91 |
• | Digital Radio Receiver (DRR), w/U2K or U2L |
• | Driver Door Module (DDM) |
• | Driver Seat Module (DSM), w/AN3 |
• | Electronic Brake Control Module (EBCM) |
• | Electronic Suspension Control (ESC) Module, w/Z55 |
• | Front Passenger Door Module (FPDM) |
• | Generator Battery Control Module (GBCM) |
• | HVAC Control Module |
• | HVAC Control Module - Rear Auxiliary |
• | Instrument Panel Cluster (IPC) |
• | Powertrain Control Module (PCM) |
• | Radio |
• | Rear Seat Audio (RSA) Controller, w/UK8 |
• | Rear Seat Entertainment (RSE) Assembly, w/U42 |
• | Rear Wheel Steering Control Module (RWSCM) |
• | Inflatable Restraint Sensing and Diagnostic Module (SDM) |
• | Transfer Case Shift Control Module (TCSCM), w/NP1/NP8 |
• | Vehicle Communication Interface Module (OnStar), w/UE1 |
• | Vehicle Theft Deterrent (VTD) Module, w/VD1 |
The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
• | U1300 |
• | U1301 |
• | U1305 |
A state of health DTC with a history status may be present along with a U1000 code having a current status. This indicates that the malfunction occurred when the ignition was ON.
Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
A poor connection at DLC terminal of the splice pack SP205 would cause this condition but will not set a DTC.
An open or a short in the class 2 serial data circuit between the DLC and splice pack SP205 will prevent the scan tool from communicating with any module. This condition will not set a DTC.
This test isolates the BCM class 2 serial data circuits.
The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must remain connected to the DLC for any other module to communicate with the scan tool. This test isolates the splice pack SP207 serial data circuits.
This test isolates the rest of the splice pack SP207 serial data circuits.
This test isolates the rest of the splice pack SP205 serial data circuits.
If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
The communication malfunction may have prevented diagnosis of the customer complaint.
Step | Action | Yes | No | ||
---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||
Does the scan tool communicate with any module on the class 2 serial data circuit? | Go to Step 3 | Go to Step 8 | |||
Did you record any DTCs in the range of U1000 to U1305? | Go to Step 4 | Go to Step 7 | |||
4 | Are the history DTCs U1300, U1301 or U1305 retrieved from any module? | Go to Step 5 | Go to Step 6 | ||
5 |
Important:: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions. Test the class 2 serial data circuit for an intermittent short to ground or an intermittent short to voltage. Refer to the following:
Did you find and correct the condition? | Go to Step 30 | Go to Step 6 | ||
Is U1000 the only DTC displayed in the previously specified range? | Go to DTC U1000 | Go to DTC U1001-U1254 | |||
Diagnose the non-communicating module by using the DTC U1001-U1254 procedure for the module which is not communicating. Refer to DTC U1001-U1254 . Did you complete the action? | Go to Diagnostic System Check - Vehicle in DTC Vehicle Information | -- | |||
8 |
Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in DTC Vehicle Information | Go to Step 9 | ||
9 | Test the DLC ground circuit at terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in DTC Vehicle Information | Go to Step 10 | ||
Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in DTC Vehicle Information | Go to Step 11 | |||
Did you find and correct the condition? | Go to Step 30 | Go to Step 12 | |||
12 |
Does the scan tool communicate with the BCM? | Go to Step 16 | Go to Step 13 | ||
Does the scan tool communicate with the BCM? | Go to Step 14 | Go to Step 15 | |||
14 |
Did you find and correct the condition? | Go to Step 30 | Go to Step 28 | ||
15 |
Did you find and correct the condition? | Go to Step 30 | Go to Step 28 | ||
Does the scan tool communicate with the BCM? | Go to Step 21 | Go to Step 17 | |||
17 |
Does the scan tool communicate with the BCM? | Go to Step 19 | Go to Step 18 | ||
18 | Repair the class 2 serial data circuit for a short to ground or a short to voltage between the splice pack SP205 and the splice pack SP207. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 30 | -- | ||
19 | Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP207 until the concern is located:
Does the scan tool communicate with the BCM? | Go to Step 30 | Go to Step 20 | ||
20 |
Did you find and correct the condition? | Go to Step 30 | Go to Step 23 | ||
Does the scan tool communicate with the BCM? | Go to Step 26 | Go to Step 22 | |||
22 |
Does the scan tool communicate with the BCM? | Go to Step 24 | Go to Step 23 | ||
23 | Repair the class 2 serial data circuit for a short to ground or a short to voltage between the splice pack SP205 and the splice pack SP206. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 30 | -- | ||
24 | Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP206 until the concern is located:
Does the scan tool communicate with the BCM? | Go to Step 30 | Go to Step 25 | ||
25 |
Did you find and correct the condition? | Go to Step 30 | Go to Step 28 | ||
Repeat the following steps on the class 2 serial data circuits connected to the splice pack SP205 until the concern is located:
Does the scan tool communicate with the BCM? | Go to Step 30 | Go to Step 27 | |||
27 |
Did you find and correct the condition? | Go to Step 30 | Go to Step 28 | ||
28 | Inspect for poor connections at the class 2 serial data circuit of the last disconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 30 | Go to Step 29 | ||
29 | Replace the last disconnected module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 30 | -- | ||
The scan tool may require a power up reset before communication will occur due to a short on the class 2 serial data circuit. Turn OFF the scan tool prior to performing this test. Did you record any DTCs which begin with a "U" and with a current status? | Refer to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 31 | |||
Did you record any DTCs which do not begin with a "U"? | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 32 | |||
32 | Use the scan tool in order to clear the DTCs. Did you complete the action? | System OK | -- |