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. Diagnostic trouble codes (DTCs) may be set due 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.
• | The BCM detects that the ignition is ON and sends the appropriate power mode message to the other modules. Therefore, the BCM must be connected to the DLC for any other module to communicate with the scan tool. |
• | When the class 2 serial data circuit is shorted to ground, U1300 will be set. Refer to DTC U1300 Class 2 Data Link Low . |
• | When the class 2 serial data circuit is shorted to B+ U1301 will be set. Refer to DTC U1301 Class 2 Data Link High . |
The number(s) below refer to the step number(s) 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:
• | Body Control Module (BCM) |
• | Driver Information Display Module |
• | Driver Seat Adjuster Memory Module |
• | Electronic Brake Control Module (EBCM) |
• | Electronic Climate Control (ECC) Module |
• | Inflatable Restraint Sensing and Diagnostic Module (SDM) |
• | Instrument Cluster |
• | Powertrain Control Module (PCM) / Vehicle Control Module (VCM) |
• | Transfer Case Shift Control Module |
• | Vehicle Interface Unit (VIU) |
The following DTCs may be retrieved with a history status, but are not the cause of the present condition.
• | U1300 |
• | U1301 |
A State of Health DTC with a history status may be present along with a U1000 or U1255 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 terminal A would cause this condition but will not set a DTC.
An open in the class 2 serial data circuit between the DLC and splice pack SP 201 will prevent the scan tool from communicating with a module. This condition will not set a DTC.
The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the BCM class 2 serial data circuit.
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 PCM/VCM class 2 serial data circuit.
This test isolates the transfer case shift control module (w/4wd) class 2 serial data circuit.
This test isolates the VIU class 2 serial data circuit.
This test isolates the EBCM class 2 serial data circuit.
This test isolates the SDM class 2 serial data circuit.
This test isolates the Instrument Cluster class 2 serial data circuit.
This test isolates the driver seat adjuster memory module (w/memory seats) class 2 serial data circuit.
This test isolates the driver information display module class 2 serial data circuit.
This test isolates the ECC class 2 serial data circuit.
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 | Value(s) | Yes | No |
---|---|---|---|---|
1 | Does the scan tool power up? | -- | Go to Step 2 | |
Does the scan tool communicate with any module on the Class 2 serial data circuit? | -- | Go to Step 3 | Go to Step 7 | |
Did you record any DTCs in the range of U1000 to U1305? | -- | Go to Step 4 | Go to Diagnostic Aids | |
4 | Are the 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 in Wiring Systems: Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 6 |
Is U1000 or U1255 the only DTC displayed in the previously specified range? | -- | Go to DTC U1000 and DTC U1255 Class 2 Communication Malfunction | ||
Did you find and correct the condition? | -- | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 8 | |
8 | Test the DLC ground circuit terminal 5 for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 9 |
Did you find and correct the condition? | -- | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 10 | |
Test the class 2 serial data circuit for an open or a short between the DLC terminal 2 and the splice pack SP201 terminal A. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Control Module References for the applicable Diagnostic System Check | Go to Step 11 | |
Does the scan tool communicate with the BCM? | -- | Go to Step 13 | Go to Step 12 | |
12 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the PCM/VCM? | -- | Go to Step 15 | Go to Step 14 | |
14 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the transfer case shift control module? | -- | Go to Step 17 | Go to Step 16 | |
16 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the VIU? | -- | Go to Step 19 | Go to Step 18 | |
18 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the EBCM? | -- | Go to Step 21 | Go to Step 20 | |
20 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the SDM? | -- | Go to Step 23 | Go to Step 22 | |
22 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Attempt to communicate with the instrument cluster. Does the scan tool communicate with the instrument cluster? | -- | Go to Step 25 | Go to Step 24 | |
24 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the driver seat adjuster memory module? (if equipped)? | -- | Go to Step 27 | Go to Step 26 | |
26 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
Does the scan tool communicate with the driver information display module? | -- | Go to Step 33 | Go to Step 28 | |
28 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 29 |
Does the scan tool communicate with the ECC? | -- | Go to Step 33 | Go to Step 30 | |
30 |
Did you find and correct the condition? | -- | Go to Step 33 | Go to Step 31 |
31 | Inspect for poor connections at the class 2 serial data circuit of the module that is not communicating. 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 33 | Go to Step 32 |
32 | Replace the module which is not communicating. Refer to Control Module References for the appropriate repair instructions. Did you complete the replacement? | -- | Go to Step 33 | -- |
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 or disconnect the scan tool prior to performing this test. Did you record any DTCs which begin with a U and with a current status? | -- | Go to Step 35 | Go to Step 34 | |
Did you record any DTCs which do not begin with a U? | -- | Go to Step 35 | Go to Step 37 | |
35 | Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction. Refer to Control Module References for the applicable Diagnostic System Check. Did you complete the action? | -- | Go to Step 36 | -- |
36 | Did you diagnose all of the DTCs? | -- | Go to Step 37 | Go to Step 35 |
37 | Use the scan tool in order to clear the DTCs. Did you complete the action? | -- | System OK | -- |