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.
- Turn ignition on. Using scan tool, review and record FAILURE RECORDS data and note parameters. Operate vehicle within FAILURE RECORDS conditions. Monitor SPECIFIC DTC INFO for this DTC until this DTC runs. If scan tool indicates that this DTC failed this ignition, go to next step. If scan tool does not indicates that this DTC failed this ignition, see DIAGNOSTIC AIDS .
- Turn ignition off. Disconnect Throttle Actuator Control (TAC) module harness connector. Check voltage between ground and TAC module ignition feed circuit. If voltage reading is zero volts, go to next step If voltage reading is not zero volts, go to step 10.
- Turn ignition on. Check voltage between ground and TAC module ignition feed circuit. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12.
- Using a test light connected to battery voltage, probe TAC module ground circuit. If test light illuminates, go to next step. If test light does not illuminate, go to step 13.
- Check voltage between ground and both TAC module serial data circuits. If voltage reading is 2-5 volts, go to step 14. If voltage reading is not 2-5 volts, go to next step.
- If voltage is greater than 2-5 volts, go to step 11. If voltage is not greater than 2-5 volts, go to next step.
- If voltage is less than 2-5 volts, go to next step.
- Check for open/short to ground in serial data circuit. Repair as necessary. After repairs, go to step 18. If circuit is okay, go to step 16.
- Repair short to voltage in ignition feed circuit. After repairs, go to step 18.
- Repair short to voltage on TAC module serial data circuit. After repairs, go to step 18.
- Repair open/short to ground in ignition feed circuit. After repairs, go to step 18.
- Repair open in TAC module ground circuit. After repairs, go to step 18.
- Check for poor serial data connections at TAC module. Repair as necessary. After repairs, go to step 18. If connections are okay, go to next step.
- Replace TAC module. After replacing module, go to step 18.
- Check for poor connections at PCM. Repair as necessary. After repairs, go to step 18. If connections are okay, go to next step.
- Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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 that set 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, diagnose affected DTCs.
NOTE:
If DTC P1120, P1220, P1221, P1515 or P1516 is set, diagnose affected DTC(s) first.
RENDER: 1.0x
NO RELATED
Recommended Tools & Savings
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
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.