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Home >> Chevrolet >> 2001 >> Camaro Base, 2D Convertible, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 7 (Engine Control System Self-Diagnostics - 5.7L) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference No. 2 Circuit ("Y" Body) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2000 Pontiac Firebird, 2000 Chevrolet Corvette, and 2000 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Start and operate engine for 2 minutes. Using scan tool, monitor DTCs. If both DTCs P1635 and P1639 failed in this ignition cycle, diagnose affected DTC(s). If only DTC P1635 failed in this ignition cycle, go to next step.
  3. If DTC P1639 failed in this ignition cycle, go to step  5. If DTC P1639 did not fail in this ignition cycle, go to next step.
  4. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS DATA for this DTC and observe parameters. Turn ignition off for 15 seconds. Start engine. Operate vehicle within conditions required for this diagnostic to run, and as close to the conditions recorded in Freeze Frame/Failure Records as possible. Using scan tool, select DTCs option, SPECIFIC DTC option, then enter this DTC. If scan tool indicates that this DTC set in this ignition cycle, go to next step. If scan tool does not indicate that this DTC set in this ignition cycle, see DIAGNOSTIC AIDS .
  5. Turn ignition off. Disconnect PCM harness connector. Using a test light connected to battery voltage, probe the 5-volt reference circuits for A/C refrigerant pressure sensor and fuel tank pressure sensor. If test light illuminates on any of the circuits, go to step  7. If test light does not illuminate on any of the circuits, go to next step.
  6. Check resistance from each 5-volt reference circuit to all other PCM circuits at PCM harness connector. If resistance on any of the circuits is 0-2 ohms, go to step  8. If resistance on any of the circuits is not 0-2 ohms, go to step  9.
  7. Repair short to ground on appropriate 5-volt reference circuit. After repairs, go to step  10.
  8. Repair short between appropriate 5-volt reference circuit and PCM circuit that had continuity. After repairs, go to step  10.
  9. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  10. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter this DTC. Operate vehicle within 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.
  11. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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