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.
Diagnostic Procedures
1999 Chevrolet Suburban C2500, 6.5 FSECTION 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.
- Start engine. Load engine by turning on several accessories (A/C, headlights, rear defogger, etc.). If actual engine speed is not greater than 200 RPM or less than 100 RPM of desired idle speed, fault is not present. See DIAGNOSTIC AIDS . If actual engine speed is greater than 200 RPM or not less than 100 RPM of desired idle speed, go to next step.
- If engine RPM is too high, go to next step. If engine RPM is not too high, go to step 5.
- Check for vacuum leaks, throttle blade not closing properly, faulty PCV system or mechanical IAC valve failure. Repair component as necessary. After repairs, go to step 6.
- Check for excessive deposits in throttle body or IAC valve passages. Check for kinked or obstructed IAC air supply hose. Inspect for IAC valve mechanical failure. Check for parasitic load on engine (transmission problem, belt driven accessory problem, etc.). Check for mechanical engine problem. Repair as necessary. After repairs, go to next step.
- Using scan tool, clear DTCs. Turn ignition off for 15 seconds. Start engine and operate vehicle. Check for DTCs. If DTC P0507 is set, go to step 2. If DTC P0507 is not set, go to next step.
- If other DTCs were present during OBD system check and have not been diagnosed, go to applicable DTC. If no other DTCs are present, 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.