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Home >> GMC >> 1997 >> Forward Control 4.3 W, L35, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (Engine Controls - Tests W/Codes - 6.5L Diesel (P Series)) >> Diagnostic Trouble Codes >> DTC P1656 - WASTEGATE Solenoid Control Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different variant/trim than selected.
  1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING article. Then go to next step.
  2. Turn ignition on, with engine off. Using scan tool, command wastegate solenoid on and off and listen for an audible click. If solenoid turns on and off, go to next step. If solenoid does not turn on and off, go to step 5).
  3. Turn ignition off. Unplug PCM harness connector containing wastegate solenoid control circuit. Turn ignition on. Using DVOM connected to ground, set DVOM on 10-amp scale and check current from PCM connector wastegate solenoid control circuit terminal. If current draw is less than .75 amp (but not zero), go to step 8). If current is not less than .75 amp (or is zero), go to next step.
  4. Turn ignition off. With PCM harness connector still unplugged, unplug wastegate solenoid connector. Check resistance between ground and PCM connector EGR solenoid control circuit terminal. If resistance is infinite, go to step 13). If not, go to step 10).
  5. Turn ignition off. Disconnect wastegate solenoid connector. Turn ignition on, with engine off. Connect test light between control circuit and ignition feed circuit of wastegate solenoid connector. If test light illuminates, go to step 9). If test light does not illuminate, go to next step.
  6. Turn ignition on, with engine off. Using test light connected to ground, probe ignition feed circuit of wastegate solenoid connector. If test light illuminates, go to step 7). If test light does not illuminate, go to step 12).
  7. Turn ignition off. Reconnect solenoid. Unplug PCM harness connector containing wastegate solenoid control circuit. Turn ignition on. With fused jumper wire connected to ground, probe PCM connector wastegate solenoid control circuit terminal. If solenoid clicks, go to step 11). If not, go to step 10).
  8. DTC is intermittent. If additional DTC(s) are set, diagnose those DTC(s). If no DTC(s) are set, see DIAGNOSTIC AIDS.
  9. Check for poor connections at wastegate solenoid. Repair terminals as necessary. After repairs, go to step 15). If connections are okay, go to step 13).
  10. Repair wastegate solenoid control circuit. After repairs, go to step 15).
  11. Check for poor connection at wastegate solenoid control terminal of PCM. Repair as necessary. After repairs, go to step 15). If connection is okay, go to step 14).
  12. Repair open in ignition feed circuit. After repair, go to step 15).
  13. Replace wastegate solenoid. After replacing solenoid, go to step 15).
  14. Replace PCM. After replacing PCM, go to next step.
  15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1656. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
  16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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