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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 544 (ENGINE CONTROLS - 3.6L (LY7) (DIAGNOSTIC INFORMATION AND PROCEDURES))DIAGNOSTIC INFORMATION AND PROCEDURESDIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLSTEST DESCRIPTION
1999 GMC Forward Control 5.7 R, Automatic

Test Description

1999 GMC Forward Control 5.7 R, AutomaticSECTION Test Description
WARNING: This page is about a different car, the 2004 Buick Rendezvous. 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. 12:  This step is for areas that have inspection and maintenance testing procedures for emissions testing. Use this step if the testing facility found one or more I/M system statuses that did not set.
A Diagnostic System Check for Engine Controls

Step Action Yes No
1 Perform the following preliminary inspections:
  • Ensure that the battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical.
  • Ensure that the battery cables are clean and tight.
  • Inspect the easily accessible systems or the visible system components for obvious damage or conditions that could cause the symptom. Refer to Strategy Based Diagnosis in General Information.
  • Ensure that the engine and control module grounds are clean, tight, and in the correct location.
  • Inspect for aftermarket devices that could affect the operation of the system. Refer to Checking Aftermarket Accessories in Wiring Systems.
  • Ensure the resistance between the ECM housing and the battery negative cable is less than 0.5 ohms.

Did you find and correct the condition?		 System OK Go to Step 2 
2
  1. Install a scan tool using the J-45289  Controller Area Network Diagnostic Interface (CANdi) Module.
  2. Turn ON the scan tool.
Does the scan tool turn ON?		 Go to Step 3  Go to Scan Tool Does Not Power Up in Data Link Communications
3
  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to establish communication with the engine control module (ECM).
Does the scan tool communicate with the ECM?		 Go to Step 4  Go to Data Link References in Data Link Communications
4
IMPORTANT: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
  1. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
  2. Rotate the ignition switch through all positions while observing the ignition switch power mode parameter. Refer to the Body Control System Description and Operation in Body Control Systems, for a list of the power mode states that correspond to each ignition switch position.
Does the ignition switch parameter reading match the ignition switch position for all switch positions?		 Go to Step 5  Go to Power Mode Mismatch in Body Control System
5 Attempt to start the engine.
Does the engine crank?		 Go to Step 6  Go to Symptoms - Engine Electrical in Engine Electrical
6 Did the engine start and idle? Go to Step 7  Go to Engine Cranks but Does Not Run
7
IMPORTANT: Do NOT clear the DTCs unless instructed by a diagnostic procedure.
  1. Select the DTC display function for the ECM and record the DTCs.
  2. If multiple powertrain DTCs are stored, diagnose the DTCs in the following order:
    1. Test for component level DTCs. For example, sensor DTCs, solenoid DTCs, and relay DTCs

      Begin with the lowest number DTC unless the diagnostic table directs you otherwise.

    2. Test for system level DTCs. For example, misfire DTCs, EVAP system DTCs and fuel trim DTCs.
  3. If there are any powertrain DTCs, Select Capture Info in order to store the Powertrain DTC information with a scan tool.
Does the scan tool display any DTCs?		 Go to Step 8  Go to Step 11 
8 Does the scan tool display DTCs which begin with a "U"? Go to Data Link References in Data Link Communications Go to Step 9 
9 Does the scan tool display DTCs P0601, P0602, P0604, or P0606? Go to DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610 Go to Step 10 
10 Does the scan tool display DTCs P0560, P0562, P0563, P0625, P0626, or P1668? Go to Diagnostic Trouble Code (DTC) List in Engine Electrical Go to Diagnostic Trouble Code (DTC) List 
11 Are there any TCM DTCs or any automatic transmission symptoms? Go to Diagnostic System Check - Automatic Transmission (3.4L) or Diagnostic System Check - Automatic Transmission (3.6L) in Automatic Transmission/Transaxle - 4T65-E Go to Step 12 
12  Is the customer's concern with Inspection and Maintenance (I/M) testing? Go to Inspection/Maintenance (I/M) System Check Go to Step 13 
13 Are there any driveability symptoms observed? Go to Symptoms - Engine Controls System OK
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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.