Test Description

The numbers below refer to the step numbers on the diagnostic table.

2: 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.
4: The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
- U1300
- U1301
6: A State of Health DTC with a history status may be present along with a U1000 with a current status. This indicates that the malfunction occurred when the ignition was ON.
10: This step will isolate a wiring problem or a module malfunction.
12: This step analyzes the impact of each connected module to class 2 bus.
18: If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.

Scan Tool Does Not Communicate with Class 2 Device

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	Turn ON the ignition, with the engine OFF. Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the Class 2 Message Monitor feature. Does the scan tool communicate with any module on the class 2 serial data circuit?	Go to Step 3	Go to Step 8
3	Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set. Record all of the displayed DTCs, the DTC status, and the module which set the DTC. Did you record any DTCs in the range of U1000 to U1255?	Go to Step 4	Go to Step 7
4	Are history DTCs U1300 or U1301 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: Testing for Intermittent Conditions and Poor Connections Circuit Testing Connector Repairs Wiring Repairs Did you find and correct the condition?	Go to Step 17	Go to Step 6
6	Is U1000 the only DTC displayed in the previously specified range?	Go to DTC U1000	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. Refer to DTC U1001-U1254 . Did you complete the action?	Go to Diagnostic System Check - Vehicle	-
8	Turn OFF the ignition. Disconnect the scan tool from the data link connector (DLC). Inspect for poor connections and terminal tension at the DLC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	Go to Diagnostic System Check - Vehicle	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 . Did you find and correct the condition?	Go to Diagnostic System Check - Vehicle	Go to Step 10
10	Disconnect all modules on the class 2 serial data circuit. Test the class 2 serial data circuits between DLC and body control module (BCM), and between all disconnected modules for an open, a short to ground, or a short to voltage. Turn ON the ignition leaving the engine OFF when testing for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition?	Go to Step 17	Go to Step 11
11	Turn OFF the ignition. Reconnect the BCM. Install the scan tool. Turn ON the ignition, with the engine OFF. Attempt to communicate with the BCM. Does the scan tool communicate with the BCM?	Go to Step Step 12	Go to Step Step 13
12	Continue connecting the disconnected modules one by one and attempt to communicate with BCM after each connection until communication can not be established or all modules are reconnected. When a module is connected, is communication lost with the class 2 serial data devices?	Go to Step 14	Go to Diagnostic Aids
13	Inspect for poor connections and terminal tension at the class 2 serial data circuit of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	Go to Step 17	Go to Step 15
14	Inspect for poor connections and terminal tension at the class 2 serial data circuit of the most recently reconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition?	Go to Step 17	Go to Step 16
15	Replace the BCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement?	Go to Step 17	-
16	Replace the most recently reconnected module. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement?	Go to Step 17	-
17	Connect all of the modules. Connect all the connectors. Install a scan tool. Turn ON the ignition, leaving the engine OFF. Wait for 10 seconds. Select the display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules do have DTCs set. Record all of the displayed DTCs and the DTC status. Did your record any DTCs which begin with a letter "U" and with a current status?	Go to Diagnostic Trouble Code (DTC) List - Vehicle	Go to Step 18
18	Did you record any DTCs which do not begin with a letter "U"?	Go to Diagnostic Trouble Code (DTC) List - Vehicle	Go to Step 19
19	Clear the DTCs using the scan tool. Did you complete the action?	System OK	-