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 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 loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
The following DTCs may be retrieved with a history status. These DTCs 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 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
Disconnecting the splice packs one at a time and attempting to communicate with any module still connected to the class 2 serial data circuit, will determine whether or not the concern is in the star portion of the class 2 serial data circuit.
Connecting the class 2 serial data circuits to the suspect splice pack one at a time while attempting to communicate with any module still connected to the class 2 serial data circuit, will determine which circuit or module on the star is causing the concern.
Splitting the class 2 serial data circuit will help isolate the location of the malfunction. If communication can be established, the concern is located in the wiring or one of the modules that is no longer connected to the DLC. If communication cannot be established, the concern is located in the wiring or one of the modules that is still connected to the DLC.
If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
The communication concern may have prevented diagnosis of the customer complaint.
Step | Action | Yes | No | ||||||||||||||||||||
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Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems | |||||||||||||||||||||||
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 8 | |||||||||||||||||||||
3 |
Did you record any DTCs in the range of U1000 to U1305? | Go to Step 4 | Go to Step 7 | ||||||||||||||||||||
Are 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 in Wiring Systems: Did you find and correct the condition? | Go to Step 21 | Go to Step 6 | ||||||||||||||||||||
Are U1000 or U1255 the only DTCs displayed in the previously specified range? | Go to DTC U1000 and U1255 | Go to DTC U1001-U1254 | |||||||||||||||||||||
7 | Diagnose the non-communicating module by using the DTC U1001-U1254 Lost Communications with XXX procedure for the module which is not communicating. The DTC U1001-U1254 Lost Communications with XXX procedure will determine which module is not communicating. Refer to DTC U1001-U1254 . Did you complete the action? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | -- | ||||||||||||||||||||
8 |
Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | Go to Step 9 | ||||||||||||||||||||
9 | Test the ground circuits of the DLC for an open or high resistance. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | Go to Step 10 | ||||||||||||||||||||
Does the scan tool communicate with the PMM? | Go to Step 12 | Go to Step 11 | |||||||||||||||||||||
11 |
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 21 | Go to Step 19 | ||||||||||||||||||||
Does the scan tool communicate with any module still connected to the class 2 serial data circuit after all the splice packs have been disconnected? | Go to Step 13 | Go to Step 14 | |||||||||||||||||||||
Using the appropriate jumper at the suspect splice pack, perform the following in order to determine which class 2 serial data circuit or module is causing the concern:
Did you complete the action? | Go to Step 18 | -- | |||||||||||||||||||||
Does the scan tool communicate with any module still connected to the class 2 serial data circuit? | Go to Step 16 | Go to Step 15 | |||||||||||||||||||||
15 | The concern is located within the ring portion of the class 2 serial data circuit still connected to the DLC. Perform the following, one module at a time starting at the module furthest from the DLC, for each module on the class 2 serial data circuit now attached to the DLC.
Does the scan tool communicate with any module still connected to the class 2 serial data circuit? | Go to Step 18 | Go to Step 17 | ||||||||||||||||||||
16 | The concern is located within the ring portion of the class 2 serial data circuit that is not connected to the DLC.
Does the scan tool communicate with any module still connected to the class 2 serial data circuit? | Go to Step 18 | Go to Step 17 | ||||||||||||||||||||
17 | Repair short to ground or voltage condition in the class 2 serial data circuits or in-line connectors to the last module disconnected in the branch being diagnosed. Refer to Wiring Repairs and Connector Repairs in Wiring Systems. Did you complete the repair? | Go to Step 21 | -- | ||||||||||||||||||||
18 | Test the class 2 serial data circuits connected to the suspect module for a short to ground or a short to voltage. Turn ON the ignition with 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 21 | Go to Step 19 | ||||||||||||||||||||
19 | Inspect for poor connections and terminal tension at the harness connector of the suspect 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 21 | Go to Step 20 | ||||||||||||||||||||
20 | Replace the suspect module. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 21 | -- | ||||||||||||||||||||
21 |
Important: 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 before you display DTCs. Did your record any DTCs which begin with a letter U and with a current status? | Go to Step 23 | Go to Step 22 | ||||||||||||||||||||
Did you record any DTCs which do not begin with a letter "U"? | Go to Step 23 | Go to Step 24 | |||||||||||||||||||||
Diagnose the DTCs as directed by the diagnostic procedures for the particular module or concern. Did you complete the action? | Go to Step 24 | -- | |||||||||||||||||||||
24 | Did you diagnose all of the DTCs? | Go to Step 25 | Go to Step 23 | ||||||||||||||||||||
25 | Clear the DTCs using the scan tool. Did you complete the action? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | -- |