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 5.7 R, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0704-P1272DTC P0704DTC P0704: CLUTCH SWITCH CIRCUIT (4.8L, 5.3L & 6.0L "C" & "K" SERIES)DIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Procedures
1999 GMC Forward Control 5.7 R, AutomaticSECTION 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, read clutch switch status. Turn ignition on, with engine off. Engage and release clutch pedal several times. If scan tool display changes when clutch is engaged and released, see DIAGNOSTIC AIDS . If scan tool display does not change, go to next step.
- Check clutch switch adjustment. Adjust if necessary. After adjustment, go to step 14. If adjustment is not necessary, go to next step.
- Turn ignition off. Disconnect clutch switch connector. Using a DVOM, check voltage between ground and clutch pedal switch ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 11.
- Turn ignition off. Disconnect clutch switch connector. Connect a fused jumper wire between clutch switch connector ignition feed and signal circuits. If scan tool displays RELEASED, go to step 8. If scan tool does not display RELEASED, go to next step.
- Turn ignition off. Disconnect PCM harness connector C1. Using DVOM, check continuity of clutch pedal signal circuit. If continuity exists, go to next step. If continuity does not exist, go to step 10.
- Check continuity between ground and clutch pedal signal circuit. If continuity exists, go to step 10. If continuity does not exist, go to step 9.
- Check for poor connections/terminal tension at clutch switch connector. Repair as necessary. After repairs, go to step 14. If connection or terminal tension is okay, go to step 12.
- Check for poor connections/terminal tension at PCM connector. Repair as necessary. After repairs, to step 14. If connection or terminal tension is okay, go to step 13.
- Repair clutch switch signal feed circuit. After repairs, go to step 14.
- Repair clutch pedal switch ignition feed circuit. After repairs, go to step 14.
- Replace clutch pedal switch. After replacing switch, go to step 14.
- Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
- 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.
- 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.