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 P0205-P0351DTC P0325DTC P0325: KNOCK SENSOR MODULE CIRCUIT (3.1L "N" & "W" BODIES & 3.4L "N" BODY & "U" SERIES)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.
- If engine knock can be heard, repair engine mechanical problem before proceeding with test. Operate vehicle within conditions required to set DTC. Using scan tool, select DTC, SPECIFIC function and enter this DTC. If scan tool display shows DTC P0325 FAILED THIS IGN, go to step 4. If scan tool display does not show DTC P0325 FAILED THIS IGN, go to next step.
- Turn ignition on, engine off. Read and record FAILURE RECORDS data for DTC P0325. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC. If scan tool displays DTC P0325 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0325 FAILED THIS IGN, see DIAGNOSTIC AIDS .
- Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
- 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 DTC P0325. Monitor scan tool until DTC P0325 test runs. If scan tool displays DTC P0325 FAILED THIS IGN, repeat step 2. If scan tool does not display DTC P0325 FAILED THIS IGN, 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.