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HOMESERVICE MANUALSCHEVROLET1999SUBURBAN C2500, 6.5 FREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P1537-U1193DTC P1639DTC P1639: 5-VOLT REFERENCE NO. 2 CIRCUIT (5.7L "F" BODY)DIAGNOSTIC PROCEDURES
1999 Chevrolet Suburban C2500, 6.5 F

Diagnostic Procedures

1999 Chevrolet Suburban C2500, 6.5 FSECTION 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 operate engine for 2 minutes. Using scan tool, monitor DTCs. If both DTCs P1635 and P1639 failed in this ignition cycle, go to DTC P1635 test. If both DTC P1635 and P1639 did not fail in this ignition cycle, go to next step.
  3. If only 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 conditions recorded in Freeze Frame/Failure Records as possible. Select DTC option, then SPECIFIC DTC option, then enter this DTC. If scan tool indicates that this DTC failed in this ignition cycle, go to next step. If scan tool does not indicate that this DTC failed 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 the A/C refrigerant pressure sensor and fuel tank pressure sensor PCM harness connector. If test light illuminates, go to step  8. If test light does not illuminate, go to next step.
  6. Turn ignition on, with engine off. Using test light connected to ground, probe PCM harness connector signal circuit for the A/C refrigerant pressure sensor and fuel tank pressure sensor. If test light illuminates on any of the circuits, go to step  9. If test light does not illuminate on any of the circuits, go to next step.
  7. Check continuity on 5-volt reference circuit and all other circuits in disconnected PCM connector. If any of the circuits indicate 0-2 ohms resistance, go to step  10. If any of the circuit does not indicate 0-2 ohms resistance, go to step  11.
  8. Repair short to ground in appropriate 5-volt reference circuit. After repairs, go to step  14.
  9. Repair short to voltage in appropriate signal circuit. After repairs, go to step  14.
  10. Repair short between appropriate 5-volt reference circuit and PCM circuit that has continuity. After repairs, go to step  14.
  11. Reconnect PCM harness connector. Turn ignition on, engine off. Using scan tool, clear DTCs. Start and operate engine at idle. Disconnect the following components one at a time, MAP, TP, EGR, fuel level and fuel tank pressure sensors. Using scan tool, monitor DTCs. If scan tool indicates that DTC P1635/P1639 passed when components were disconnected, go to next step. If scan tool does not indicate that DTC P1635/P1639 passed when components were disconnected, go to step  13.
  12. Replace component which caused DTC to pass when it was disconnected. After replacing component(s), go to step  14.
  13. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  14. 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.
  15. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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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.