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 Buick Regal LSSECTION 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.
- Review FAILURE RECORDS data. If other DTCs are stored, diagnose affected DTCs. If no other DTCs are present, go to next step.
- Perform CKP System Variation Learn Procedure. See appropriate BASIC DIAGNOSTIC PROCEDURES article. After performing CKP learn procedure, go to next step.
- Start and allow engine to idle. Using scan tool, monitor MAP sensor voltage. If voltage reading is greater than 4 volts, go to DTC P0108 for diagnosis. If voltage reading is not greater than 4 volts, go to next step.
- Turn ignition off, then turn ignition on, with engine off. Duplicate conditions required to set DTC. Using scan tool, read DTC PRESENT THIS IGNITION CYCLE. If the scan tool displays DTC P0300, PRESENT THIS IGN, go to next step. If the scan tool does not display DTC P0300, PRESENT THIS IGN, go to step 11.
- Using scan tool, review misfire index. If misfire index is increasing for more than one cylinder, see DIAGNOSTIC AIDS . If misfire index is not increasing for more than one cylinder, go to next step.
- Install a spark tester on No. 1 spark plug wire. Disconnect fuel injector harness at intake manifold. Crank engine and check for spark at tester. Repeat procedure for each spark plug wire. If spark is adequate on all wires, go to next step. If spark is not adequate, diagnose ignition system. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
- Remove and check spark plugs for wear, excessive gap, cracks or fouling. If spark plugs are okay, go to next step. If spark plugs are not okay, go to step 12.
- Perform cylinder compression test. If engine mechanical problem is found, repair as necessary. After repairs, go to step 14. If no mechanical problem is found, go to next step.
- Perform injector circuit test. See appropriate BASIC DIAGNOSTIC PROCEDURES article. If fuel system is okay, go to next step. If fuel system is not okay, go to step 13.
- DTC is intermittent. Check if additional DTCs are present. Diagnose affected DTCs. If no additional DTCs are present, see DIAGNOSTIC AIDS .
- Replace spark plugs. After replacing spark plugs, go to step 14.
- Repair as necessary. After repairs, go to next step.
- Using scan tool, select DTC, CLEAR INFO function. Start engine and allow it to reach operating temperature. Using scan tool, select DTC, SPECIFIC function and enter this DTC. Operate vehicle within conditions required to set 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.
- Using scan tool, select Read and Record INFO, REVIEW INFO function. Check if any undiagnosed DTCs are displayed. Diagnose affected DTCs. If no additional DTCs are displayed, 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.