Diagnostic Procedure

The control module identification number list provides a method for determining which module is not communicating. The diagnostic procedure assumes that all modules are powered. A module with an internal Class 2 circuit malfunction or which loses power during the current ignition cycle would have a Lost Communication DTC set by the other modules. Use the control module identification number in order to determine which module is not communicating. The control module identification numbers are as follows:

• 016
  
  BCM/VCM
• 026
  
  ATC Control Module
• 041
  
  EBCM
• (No ID #)
  
  Instrument Cluster

The EBCM may set Class 2 Lost Communication DTCs when the BCM or the powertrain control module (PCM/VCM) is being reprogrammed. After reprogramming, test for DTCs in the EBCM. When only DTCs which begin with a "U" are set with a history status, clear the DTCs. If there are any current DTCs, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  under SELF-DIAGNOSTIC SYSTEM.

1. Perform the Diagnostic System Check for the module which does not communicate in order to ensure that the module is properly powered. See DIAGNOSTIC SYSTEM CHECK in appropriate BODY CONTROL MODULES article, ANTI-LOCK article in BRAKES, SELF-DIAGNOSTICS INTRODUCTION article in ENGINE PERFORMANCE, INSTRUMENT PANEL article or TRANSFER CASE article. If no fault was found and corrected, go to next step. If a fault was found and corrected, go to step  10 .
2. Turn the ignition switch to the OFF position. Disconnect the module which does not communicate. Inspect for a proper connection of the Class 2 serial data circuit to the module which does not communicate. If the connection is good, go to next step. If the connection is faulty, go to step  9 .
3. Measure the resistance of the Class 2 serial data circuit from the connector of the module which does not communicate to the data link connector terminal No. 2. If the resistance is not 0-5 ohms, go to next step. If the resistance is 0-5 ohms, go to step  7 .
4. Disconnect splice pack (SP205). Inspect for a proper connection of the Class 2 serial data circuit from the module which does not communicate to the splice pack. If the connection is good, go to next step. If the connection is faulty, go to step  9 .
5. Measure the resistance of the Class 2 serial data circuit from the connector of the module which does not communicate to the SP205. If the resistance is 0-5 ohms, go to next step. If the resistance is not 0-5 ohms, go to step  8 .
6. Repair or replace the SP205. Go to step  10 .
7. Replace the module which does not communicate.
8. Repair the open in the Class 2 serial data circuit of the module which does not communicate. Go to step  10 .
9. Repair the connection. Go to next step.
10. Turn the ignition switch to the RUN position. Wait for 10 seconds. Inspect for DTCs in the module which would not communicate. If there are no DTCs that begin with a "U" prefix, go to next step. If there are DTCs present that do not begin with a "U" prefix, go to step  14 .
11. If there are only DTCs with a "U" prefix, clear all DTCs. Go to next step.
12. Inspect for DTCs in each module which had the Class 2 Lost Communication DTCs set as a current DTC. If there are no DTCs that begin with a "U" prefix, go to next step. If there are any DTCs present that do not have a "U" prefix, go to step  14 .
13. If there are only DTCs with a "U" prefix, clear all DTCs. System should be okay.
14. Diagnose the DTCs as directed by the diagnostic procedures for the particular module. See appropriate BODY CONTROL MODULES article, ANTI-LOCK article in BRAKES, SELF-DIAGNOSTICS INTRODUCTION article in ENGINE PERFORMANCE, INSTRUMENT PANEL article or TRANSFER CASE article. Go to step  11 .

A current DTC U1xxx (where xxx is equal to the 3-digit identification number) will clear when a Node Alive message from the failed identification number is detected on the Class 2 serial data link or at the end of the current ignition cycle. A history DTC U1xxx will clear upon receipt of a scan tool Clear DTCs command.