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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 77 (ENGINE CONTROLS SELF-DIAGNOSTICS - 6.5L)DIAGNOSTIC TESTSDTC P1656: WASTEGATE SOLENOID CONTROL CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: Ensure that both the ON and OFF states are commanded. Repeat the commands as many times as necessary. This step will determine if this DTC is a current or an intermittent.
  2. Connect the scan tool. Turn ON the ignition, with the engine OFF. With the scan tool, command the wastegate solenoid ON and OFF and listen for an audible click. Does the solenoid turn ON and OFF (audible click) with each command? If yes, go to next step. If no, go to step  5 .
  3. Turn OFF the ignition. Disconnect the PCM connector containing the wastegate solenoid control circuit. Turn ON the ignition. Use a Digital Multimeter (DMM) on a 10-amp scale in order to measure the current from the solenoid control circuit in the PCM harness connector to ground for 2 minutes. Is the current draw less than 0.75 A, but not zero? If yes, go to step  8 . If no, go to next step.
  4. Turn OFF the ignition. Leaving the PCM connector disconnected, disconnect the wastegate solenoid. Use a DMM, in order to measure the resistance from the solenoid control circuit in the PCM harness connector to ground. Does the DMM display an infinite resistance? If yes, go to step  13 . If no, go to step  10 .
  5. Disconnect the wastegate solenoid. Turn ON the ignition, with the engine OFF. Connect a Unpowered Test Lamp (J 34142-B) between the boost solenoid control circuit and the ignition feed circuit at the harness connector. Use a scan tool in order to command the solenoid ON and OFF. Does the J 34142-B turn ON and OFF with each command? If yes, go to step  9 . If no, go to next step.
  6. Turn ON the ignition, with the engine OFF. With a J 34142-B connected to ground, probe the ignition feed circuit at the wastegate solenoid harness connector. Does the test lamp illuminate? If yes, go to next step. If no, go to step  12 .
  7. Turn OFF the ignition. Reconnect the solenoid. Disconnect the PCM harness containing the solenoid control circuit. Turn ON the ignition. With a fused jumper wire connected to ground, probe the solenoid control circuit in the PCM harness connector. Does the solenoid operate? If yes, go to step  11 . If no, go to step  10 .
  8. The DTC is intermittent. If no additional DTCs are stored, see DIAGNOSTIC AIDS  . If any additional DTCs are stored, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
  9. Check for a poor connection at the wastegate solenoid and replace the terminal if necessary. Did you perform a repair? If yes, go to step  15 . If no, go to step  13 .
  10. Repair the wastegate solenoid control circuit. After repairs, go to step  15 .
  11. Check for a poor connection at the PCM wastegate control circuit. Repair as necessary. Did you perform a repair? If yes, go to step  15 . If no, go to step  14 .
  12. Repair the open in the ignition feed circuit. After repairs, go to step  15 .
  13. Replace the wastegate solenoid. After repairs, go to step  15 .
  14. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  15. Using the scan tool, clear the DTCs. Start engine and idle the engine at the normal operating temperature. Select DTC and the Specific DTC function. Enter the DTC number that was set. Operate the vehicle within the Conditions for Setting DTC until the scan tool indicates the diagnostic ran. Does the scan tool indicate the diagnostic passed? If yes, go to next step. If no, go to step  2 .
  16. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, system is okay.
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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.