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Home >> GMC >> 1999 >> Forward Control 6.5 Y, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Tests W/Codes - Diesel >> Diagnostic Tests >> DTC P0303: Cylinder No. 3 Misfire Detected ("C", "G", "K" & "P" Series) >> Diagnostic Procedures

Diagnostic Procedures

  1. If OBD system check has been performed, go to next step. If OBD system check has not been performed, go to ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Install scan tool. Start and idle engine. Operate engine at normal operating temperature. Using scan tool, cut out (injector balance) the suspected cylinder. If RPM drops in suspected cylinder, go to next step. If RPM does not drop in suspected cylinder, go to step  4.
  3. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS . If any additional DTCs are set, go to applicable DTC test.
  4. Check for basic engine mechanical or fuel delivery problem (i.e., injection nozzle malfunction, intake manifold restriction) in suspected cylinder. Repair as necessary. After repairs, go to step  6. If repairs were not necessary, go to next step.
  5. Replace fuel injection pump. If fuel injection pump is replaced, new pump must be timed. See appropriate ON-VEHICLE ADJUSTMENTS article. After replacing injection pump, go to next step.
  6. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0303. 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.
  7. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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