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Test Description

WARNING: This page is about a different car, the 2004 Cadillac Seville. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  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.
  2. 4:  The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
    • U1300
    • U1301
    • U1305
  3. 6:  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.
  4. 10:  Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
  5. 12:  An open between the DLC and the class 2 serial data circuit will prevent the scan tool from communicating with any module. This condition will not set a DTC.
  6. 13:  Splitting the class 2 serial data circuit will help isolate the location of the malfunction. If communication can be established, the malfunction is located in the wiring or one of the modules that is no longer connected to the DLC. If communication cannot be established, the malfunction is located in the wiring or one of the modules that is still connected to the DLC.
  7. 21:  If there are no current DTCs that begin with the letter "U", the communication malfunction has been repaired.
  8. 22:  The communication malfunction may have prevented diagnosis of the customer complaint.
Scan Tool Does Not Communicate with Class 2 Device

Step Action Yes No
Schematic Reference:  Data Link Connector (DLC) 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  Go to Scan Tool Does Not Power Up 
2 
  1. Turn ON the ignition, with the engine OFF.
  2. 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
  1. 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.
  2. 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 U1305?		 Go to Step 4  Go to Step 7 
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 18  Go to Step 6 
6  Are DTCs U1000 and 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 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 Control Module References for the applicable Diagnostic System Check -
8
  1. Turn OFF the ignition.
  2. Disconnect the scan tool from the data link connector (DLC).
  3. Inspect for poor connections and terminal tension at the DLC. Refer to the following:
Did you find and correct the condition?		 Go to Control Module References for the applicable Diagnostic System Check Go to Step 9 
9 Test the ground circuits of the DLC for an open or high resistance. Refer to the following:
Did you find and correct the condition?		 Go to Control Module References for the applicable Diagnostic System Check Go to Step 10 
10  Test the class 2 serial data circuit between the DLC and first 2 modules on the class 2 serial data circuit for the following conditions:
  • A high resistance
  • An open
  • A short to ground
  • A short to voltage

Refer to the following:
Did you find and correct the condition?		 Go to Control Module References for the applicable Diagnostic System Check Go to Step 11 
11
  1. Turn OFF the ignition.
  2. Split the class 2 serial data circuit in half by disconnecting 2 modules in order to help isolate the location of the fault within the class 2 serial data circuit. The DLC must remain connected to at least 1 module. Refer to Diagnostic Aids for suggested disconnection locations.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with modules still connected to the DLC through the class 2 serial data circuit.
Does the scan tool communicate with any module still connected to the class 2 serial data circuit?		 Go to Step 13  Go to Step 12 
12  The fault is located within the 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.
  1. Turn OFF the ignition.
  2. Disconnect the furthest module from the DLC still connected to the class 2 serial data circuit.
  3. Turn ON the ignition, with the engine OFF.
  4. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.
  5. Repeat steps 1 through 4 above, until communication is restored.

Does the scan tool communicate with modules on the class 2 serial data circuit?		 Go to Step 15  Go to Step 14 
13  The fault is located within the portion of the class 2 serial data circuit that is not connected to the DLC.
  1. Connect one of the modules that was disconnected to split the serial data circuit.
  2. 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.
    1. Turn OFF the ignition.
    2. Disconnect the furthest module from the DLC still connected to the class 2 serial data circuit.
    3. Turn ON the ignition, with the engine OFF.
    4. Attempt to communicate with any module still connected to the DLC through the class 2 serial data circuit.
    5. Repeat steps 2.1 through 2.4 until communication is restored.

Does the scan tool communicate with any module on the class 2 serial data circuit?		 Go to Step 15  Go to Step 14 
14 Repair the class 2 serial data circuits and in-line connectors to the last module connected in the branch being diagnosed.
Did you complete the repair?		 Go to Step 18  -
15 Test the class 2 serial data circuits connected to the last module disconnected for the following conditions:
  • A short to ground
  • A short to voltage

Turn ON the ignition with the engine OFF when testing for a short to voltage.
Refer to the following:
Did you find and correct the condition?		 Go to Step 18  Go to Step 16 
16 Inspect for poor connections and terminal tension at the harness connector of the last module disconnected. Refer to the following:
Did you find and correct the condition?		 Go to Step 18  Go to Step 17 
17
IMPORTANT: Perform the module setup procedure if required.
Replace the last module disconnected. Refer to Control Module References in Body Control System for the appropriate repair instructions for module replacement.Did you complete the replacement?		 Go to Step 18  -
18
  1. Connect all of the modules.
  2. Connect all the connectors.
  3. Install a scan tool.
  4. Turn ON the ignition leaving the engine OFF.
    5. 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.
  5. Wait for 10 seconds.
  6. 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.
  7. 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 Step 20  Go to Step 19 
19 Did you record any DTCs which do not begin with a letter "U"? Go to Step 20  Go to Step 21 
20 Diagnose the DTCs as directed by the diagnostic procedures for the particular module or malfunction.
Did you complete the action?		 Go to Step 21  -
21  Did you diagnose all of the DTCs? Go to Step 22  Go to Step 20 
22  Clear the DTCs using the scan tool.
Did you complete the action?		 System OK -
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