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
1996 Buick Roadmaster LimitedSECTION Diagnostic Procedures
- Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
- Turn ignition on, with engine off. Using scan tool, command A/C relay on and off. If relay turns on and off as commanded, go to next step. If relay does not turn on an off as commanded, go to step 5).
- Turn ignition off. Disconnect PCM containing relay control circuit. Turn ignition on. Using DVOM on 10-amp scale, measure current from relay control circuit in PCM harness connector to ground for 2 minutes. If current draw is less that .75 amps, but not zero, see DIAGNOSTIC AIDS. If current draw is not as specified, go to next step.
- Turn ignition off. Disconnect relay. Using DVOM, check resistance from relay control circuit in PCM connector to ground. If resistance is infinity, go to step 12). If resistance is not as specified, go to step 12).
- Turn ignition off. Disconnect relay. Connect test light between relay coil terminals in relay harness connector. Turn ignition on. Using scan tool, command relay on and off. If test light illuminates with each command, go to step 8). If test light does not illuminate with each command, go to next step.
- Connect test light to ground and probe battery feed circuits in relay harness connector. If test light illuminates on both terminals, go to next step. If test light does not illuminate on both terminals, go to step 11).
- Turn ignition off. Reconnect A/C relay. Disconnect PCM harness connector containing relay control circuit. Turn ignition on. Using a fused jumper wire, jumper relay control circuit in PCM harness connector to ground. If relay activates, go to step 9). If relay does not activate, go to step 10).
- Check connections at relay. Repair as necessary. After repairs, go to step 14). If connections are okay, go to step 12).
- Check connections at PCM. Repair as necessary. After repairs, go to step 14). If connections are okay, go to step 13).
- Repair faulty relay control circuit. After repairs, go to step 14).
- Repair faulty battery feed circuit. After repairs, go to step 14).
- Replace A/C relay. After replacing relay, 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 DTC P1545. 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 did not indicate that this test ran and passed, repeat step 2).
- Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) 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.