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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 839 (DATA LINK COMMUNICATIONS)DIAGNOSTIC INFORMATION AND PROCEDURESSCAN TOOL DOES NOT COMMUNICATE WITH KEYWORD DATA LINEDIAGNOSTIC AIDS
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Aids

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Aids
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.
  • If the malfunction is intermittent, check for poor connections at the suspect module. Wiggling the harness wiring may help in locating the fault.
  • Diagnostic trouble codes (DTCs) may be set do to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.
Scan Tool Does Not Communicate with Keyword Data Line

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
  1. Connect the scan tool to the DLC.
  2. Turn ON the ignition, with the engine OFF.
  3. Attempt to communicate with each module on the keyword serial data circuit:
    • The engine control module (ECM)
    • The transmission control module (TCM)
    • The electronic brake control module (EBCM)
Does the scan tool communicate with all the modules on the keyword serial data circuit?		 Go to Testing for Intermittent Conditions and Poor Connections In Wiring Systems Go to Step 3 
3
  1. Disconnect the scan tool from the DLC.
  2. Turn OFF the ignition.
  3. Disconnect all non-communicating modules on the keyword serial data circuit.
  4. Turn the ignition ON, with the engine OFF.
  5. Test the keyword serial data circuit between the DLC and all the modules on the keyword serial data circuit, for the following conditions:
    • An open
    • A short to ground
    • A short to voltage
Refer to the following:Did you find and correct the condition?		 Go to Step 7  Go to Step 4 
4 Test the following circuits of the module that is not communicating for an open or high resistance:
  • The battery positive voltage input circuits
  • The battery positive voltage output circuits
  • The ignition voltage input circuits
  • The ignition voltage output circuits
  • The switched battery positive voltage supply circuits
  • The ground circuits

Refer to the following:
Did you find and correct the condition?		 Go to Step 7  Go to Step 5 
5 Inspect for poor connections and terminal tension at the following harness connector circuits of the module that is not communicating :
  • The battery positive voltage input circuits
  • The battery positive voltage output circuits
  • The ignition voltage input circuits
  • The ignition voltage output circuits
  • The switched battery positive voltage supply circuits
  • The ground circuits
  • The Keyword serial data circuits

Refer to the following:
Did you find and correct the condition?		 Go to Step 7  Go to Step 6 
6
IMPORTANT: Perform the programming or set up procedure for the replaced control module if required.
Replace the module that is not communicating on the Keyword serial data circuit. Refer to Control Module References in Body Control System for the applicable replacement procedure.Did you complete the replacement?		 Go to Step 7  -
7
  1. Connect all modules and connectors.
  2. Connect the scan tool to the DLC.
  3. Turn ON the ignition, with the engine OFF.
  4. Perform the Diagnostic System Check for the system exhibiting symptoms. Refer to Control Module References in Body Control System.
Did you complete the operation?		 System OK Go to Step 2 
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.