LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2002 >> Escalade EXT >> Repair and Diagnosis >> External Pages >> Different car >> Section 1341 (Data Link Communications) >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Class 2 Device >> Test Description
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Test Description

WARNING: This page is about a different car, the 2003 Saturn Vue. 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. 3:  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.
  2. 5:  The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition.
    • U1300
    • U1301
  3. 7:  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.
  4. 11:  This step will isolate a wiring problem or a module malfunction.
  5. 13:  This step analyzes the specific branch circuit for a malfunction.
  6. 14:  An open circuit at this point will cause a loss of communication with the vehicle.
  7. 19:  If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
  8. 21:  The communication concern 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 (A/T)  or Data Link Connector (DLC) Schematics (M/T) 
Connector End View Reference: Master Electrical Component List in Wiring Systems
1 Did you perform the Diagnostic System Check for the system exhibiting symptom? Go to Step 2  Go to Control Module References in Body Control System for the applicable Diagnostic System Check
2 Install a scan tool.
Does the scan tool power up?		 Go to Step 3  Go to Scan Tool Does Not Power Up 
3 
  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 4  Go to Step 9 
4
  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 U1255?		 Go to Step 5  Go to Step 8 
5  Are history DTCs U1300 or U1301 retrieved from any module? Go to Step 6  Go to Step 7 
6
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 7 
7  Is U1000 the only DTC displayed in the previously specified range? Go to DTC U1000  Go to DTC U1001-U1254 
8 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 Control Module References in Body Control Systems for the applicable Diagnostic System Check -
9
  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 Testing for Intermittent Conditions and Poor Connections and Connector 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 10 
10 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 Control Module References in Body Control Systems for the applicable Diagnostic System Check Go to Step 11 
11 
  1. Disconnect all modules on the class 2 serial data circuit.
    2. IMPORTANT: Turn ON the ignition, leaving the engine OFF, when testing for a short to voltage.
  2. Test the class 2 serial data circuit for a short to ground or short to voltage between DLC terminal 2 and each module on the class 2 serial data circuit.
Did you find and correct the condition?		 Go to Step 18  Go to Step 12 
12
  1. Turn OFF the ignition.
  2. Reconnect the BCM.
  3. Install the scan tool.
  4. Turn the ignition ON, with the engine OFF.
  5. Attempt to communicate with the BCM.
Does the scan tool communicate with the BCM?		 Go to Step Step 13  Go to Step Step 14 
13  Continue connecting the disconnected modules and attempting to communicate 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 15  Refer to Diagnostic Aids
14  Inspect for poor connections and terminal tension at the class 2 serial data circuit of the BCM.
Did you find and correct the condition?		 Go to Step 18  Go to Step 16 
15 Inspect for poor connections and terminal tension at the class 2 serial data circuit of the most recently reconnected module.
Did you find and correct the condition?		 Go to Step 18  Go to Step 17 
16
IMPORTANT: Perform the programming or set up procedure for the replaced control module if required.
Replace the BCM. Refer to Body Control Module Replacement in Body Control System for the applicable replacement procedure.Did you complete the replacement?		 Go to Step 18  -
17
IMPORTANT: Perform the programming or set up procedure for the replaced control module if required.
Replace the most recently reconnected module. Refer to Control Module References in Body Control System for the appropriate replacement procedure.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 22 
20 Diagnose the DTCs as directed by the diagnostic procedures for the particular module or concern.
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?		 Go to Control Module References in Body Control Systems for the applicable Diagnostic System Check -
scientia non olet · About LEMON Manuals