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HOMESERVICE MANUALSCHEVROLET1999MONTE CARLO LS, 3.8 KREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0352-P0452DTC P0401DTC P0401: EGR SYSTEM-INSUFFICIENT FLOW (4.3L "L", "M", "S" & "T" SERIES)DIAGNOSTIC PROCEDURES
1999 Chevrolet Monte Carlo LS, 3.8 K

Diagnostic Procedures

1999 Chevrolet Monte Carlo LS, 3.8 KSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
  2. Start and warm engine to normal operating temperature. Operate engine at greater than 1500 RPM. Using scan tool, command EGR duty cycle through 25, 50, 75 and 100 percent positions. If engine runs rough as EGR is cycled, go to step  5. If engine does not run rough, go to next step.
  3. Turn engine off. Turn ignition on, engine off. Disconnect EGR valve harness connector. Connect a test light between EGR valve harness connector ignition feed and control circuits. If test light does not illuminate, go to next step. If test light illuminates, go to step  7.
  4. Start engine. Using scan tool, select MISCELLANEOUS TESTS, EGR CONTROL. With test light still connected, command EGR duty cycle increase to 100 percent. If test light illuminates as EGR is cycled, go to step  8. If test light does not illuminate, go to step  11.
  5. Remove EGR valve and inspect valve and passages for damage. Inspect valve pintle to ensure it is not sticking partially open. If a problem is found, go to step  10. If no problem is found, go to next step.
  6. DTC is intermittent. Check if additional DTCs are present. Diagnose affected DTCs. If no additional DTCs are present, see DIAGNOSTIC AIDS .
  7. Check for short to ground in EGR valve control circuit. If circuit is shorted, go to step  14. If circuit is okay, go to step  15.
  8. Check for restriction in EGR tube or passage. If restriction is found, go to step  10. If no restriction is found, go to next step.
  9. Check for faulty electrical connection at EGR valve. If faulty connection is found, go to step  14. If connection is okay, go to next step.
  10. Replace faulty EGR valve. After replacing EGR valve, go to step  16.
  11. Check for an open in EGR control circuit. If circuit is open, go to step  14. If circuit is okay, go to next step.
  12. Check for an open in EGR ignition feed circuit. If circuit is open, go to step  14. If circuit is okay, go to next step.
  13. Check for faulty connection at VCM. If connection is faulty, go to next step. If connection is okay, go to step  15.
  14. Repair circuit as necessary. After repairs, go to step  16.
  15. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
  16. Using scan tool, select DTC, CLEAR INFO function. Start engine and allow it to reach operating temperature. Using scan tool, select DTC, SPECIFIC function and enter this DTC. Operate vehicle within conditions required to set DTC. If scan tool indicates that this DTC RAN AND PASSED, go to next step. If scan tool does not display that this DTC RAN AND PASSED, repeat step  2.
  17. Using scan tool, select Read and Record INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no DTCs are displayed, 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.