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, with engine off. Using scan tool in ENGINE 3 mode, note A/C LOW SIDE TMP. display. If scan tool display reads -35 to 210°F (-37 to 99°C), fault is not present. Diagnose A/C-heater system. See appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. If scan tool display reads less than -35°F (-37°C) or greater than 210°F (99°C), go to next step.
- If temperature displayed is less than -35°F (-37°C), go to next step. If temperature displayed is greater than -35°F (-37°C), go to step 7.
- Turn ignition off. Disconnect sensor harness connector. Using jumper wire, jumper A/C low temperature sensor harness connector terminals. Turn ignition on. If temperature reading is greater than 210°F (99°C), go to step 12. If temperature reading is less than 210°F (99°C), go to next step.
- Remove jumper wire from sensor harness connector. Jumper sensor harness connector terminal "A" to ground. If temperature reading is greater than 210°F (99°C), go to step 9. If temperature reading is not greater than 210°F (99°C), go to next step.
- Remove jumper wire from sensor connector. Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Using DVOM, check resistance of A/C low temperature sensor signal circuit between PCM and sensor harness connector terminals. If resistance is greater than 5 ohms, go to step 10. If resistance is not greater than 5 ohms, go to step 14.
- Disconnect sensor harness connector. If temperature displayed is less than -35°F (-37°C), go to step 12. If temperature displayed is not less than -35°F (-37°C), go to next step.
- Store fluid life index as indicated on scan tool. Turn ignition off and wait 30 seconds, then disconnect PCM harness connector C1. Using DVOM, check resistance between ground and A/C low temperature sensor circuit at PCM harness connector C1 terminal. If resistance is greater than 10,000 ohms, go to step 14. If resistance is not greater than 10,000 ohms, go to next step.
- Repair open in A/C low temperature sensor ground circuit.
- Repair open in A/C low temperature sensor circuit.
- Repair short to ground in A/C low temperature sensor circuit.
- Check terminal contact at sensor harness connector. Repair as necessary. If terminal contact is okay, go to next step.
- Replace A/C low temperature sensor.
- Check terminal contact at PCM harness connector C1. Repair as necessary. If terminal contact is okay, go to next step.
- Replace PCM. Program replacement PCM using required equipment.
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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.