1999 GMC Forward Control 5.7 R, AutomaticFACTORY OEM SERVICE PROCEDURE

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. NOTE: If any DTCs are set (except P1153 and/or P1154), diagnose affected DTCs first.
  2. Warm engine to normal operating temperature. Operate vehicle within conditions required to set this DTC. Using scan tool, read SPECIFIC DTC. If scan tool displays that this DTC failed this ignition, go to next step. If scan tool does not display that this DTC failed this ignition, see DIAGNOSTIC AIDS .
  3. If scan tool indicates that DTC P1153 and/or P1154 failed, go to step  8. If scan tool does not indicate that DTC P1153 and/or P1154 failed, go to next step.
  4. Check exhaust system for leaks. Repair as necessary. After repairs, go to step  14. If no exhaust leak is found, go to next step.
  5. Visually inspect HO2S 1 for secure installation or corrosion on terminals. Check terminal tension at HO2S and PCM. Check for damaged wiring. Repair as necessary. After repairs, go to step  14. If no problem is found, go to next step.
  6. Disconnect HO2S harness connector. Connect a jumper wire between HO2S harness connector low (ground) circuit and chassis ground. Using scan tool, monitor HO2S voltage. If voltage reading is 350-550 mV, go to next step. If voltage reading is not 350-550 mV, go to step  10.
  7. Connect a jumper wire between chassis ground and HO2S harness connector signal and low (ground) circuits. Using scan tool, monitor HO2S voltage. If voltage reading is less than 200 mV, go to step  13. If voltage reading is not less than 200 mV, go to step  9.
  8. Repair condition causing fuel, sealant, oil or coolant contamination. Replace affected HO2S. After replacing sensor, go to step  14.
  9. Check voltage between ground and HO2S low circuit. If voltage reading is about 5 volts, go to step  12. If voltage reading is not about 5 volts, go to step  11.
  10. Repair short to ground or short to voltage in HO2S signal circuit. After repairs, go to step  14.
  11. Repair open in HO2S low circuit or faulty PCM connections. After repairs, go to step  14.
  12. Repair open in HO2S signal circuit or faulty PCM connections. After repairs, go to step  14.
  13. Replace HO2S. After replacing sensor, go to next step.
  14. Using scan tool, read and record FAILURE RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for this DTC. If scan tool displays that this DTC FAILED THIS IGN, return to step  2. If scan tool does not display that this DTC FAILED THIS IGN, go to next step.
  15. Using scan tool, select CAPTURE INFO and REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs.
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.