Modules connected to the class 2 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. 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 circuit is shorted to battery negative voltage, U1300 will be set. Refer to DTC U1300 . |
• | When the class 2 circuit is shorted to battery positive voltage U1301 will be set. Refer to DTC U1301 . |
The numbers below refer to the step numbers on the diagnostic table.
A partial malfunction in the class 2 circuit uses a different procedure from a total malfunction of the class 2 circuit. The following modules communicate on the class 2 circuit:
• | Electronic climate control module (ECCM) |
• | Transfer case shift control module (TCSCM) |
• | Electronic brake control module (EBCM) |
• | Powertrain control module (PCM) |
• | Vehicle interface unit (VIU) |
• | Body control module (BCM) |
• | Instrument panel cluster (IPC) |
• | Driver information center (DIC) |
• | Memory seat module (MSM) |
• | Inflatable restraint sensing and diagnostic module (SDM) |
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.
DLC 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 circuit between the DLC and SP201 will prevent the scan tool from communicating with a module. This condition will not set a DTC.
The class 2 circuit is shorted to battery positive voltage or battery negative voltage. 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 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 class 2 circuit.
This test isolates the TCSCM class 2 circuit.
This test isolates the VIU class 2 circuit.
This test isolates the EBCM class 2 circuit.
This test isolates the SDM class 2 circuit.
This test isolates the IPC class 2 circuit.
This test isolates the MSM class 2 circuit.
This test isolates the DIC class 2 circuit.
This test isolates the ECCM class 2 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 | Yes | No |
---|---|---|---|
Schematic Reference: Data Link Connector Schematics | |||
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 6 | 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 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 U1255 | Go to DTC U1001-U1254 | |
Did you find and correct the condition? | Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check | Go to Step 8 | |
8 | Test the DLC signal return circuit 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 in Body Control Systems for the applicable Diagnostic System Check | Go to Step 9 |
Did you find and correct the condition? | Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check | Go to Step 10 | |
Test the DLC class 2 circuit for an open or a short. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Control Module References in Body Control Systems 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? | 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 TCSCM? | 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 IPC. Does the scan tool communicate with the IPC? | 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 MSM? | 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 DIC? | 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 ECCM? | 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 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 in Body Control Systems 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 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 in Body Control Systems 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 | -- |