Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 4.3 W, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P1537-U1193DTC P1632DTC P1632: THEFT DETERRENT SYSTEM FUEL DISABLED (2.2L "S" SERIES & 2.4L "N" BODY)DIAGNOSTIC PROCEDURES
1999 GMC Forward Control 4.3 W, Standard
Diagnostic Procedures
1999 GMC Forward Control 4.3 W, StandardSECTION Diagnostic Procedures
- 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.
- Using scan tool, check if DTCs P1626, P1630 or P1631 is also set. Diagnose affected DTC(s). If DTCs are not set, go to next step.
- Perform Password Learn Procedure. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. Attempt to start engine. If engine starts and continues to run, go to step 8. If engine does not start or starts and then stalls, go to next step.
- Using scan tool, display data list for BFC or TBC (trucks). If scan tool indicates that Passlock® data is valid, go to next step. If scan tool does not indicate that Passlock® data is valid, go to step 6.
- Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to step 8.
- Check if there are any theft deterrent related DTCs set. Diagnose affected DTCs. If no theft deterrent related DTCs are set, go to next step.
- Diagnose theft deterrent system. See appropriate ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. After repairs, go to next step.
- Using scan tool, clear DTCs. Warm engine to normal operating temperature. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this DTC ran and passed, go to next step. If scan tool does not indicate that this DTC ran and passed, repeat step 2.
- Check if additional DTC are set. Diagnose affected DTCs. If no other DTCs are set, 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.