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.NOTE: If other DTC(s) are present, except for P0171, diagnose other DTC(s) first.
- Start and warm engine to normal operating temperature. Ensure system is in "closed loop". Using scan tool, select FUEL TRIM DATA LIST and monitor LT FT and ST FT for bank 2. If LT FT AVG. BN. 2 is less than 22 percent and ST FT AVG. BN. 2 is less than 10 percent, go to next step. If displayed value is not less than specification, go to step 4).
- Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within the conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function then enter DTC P0174. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see DIAGNOSTIC AIDS.
- If DTC P0171 is also present, go to next step. If DTC P0171 is not present, go to step 6).
- Check vacuum hoses for splits, kinks and proper routing. Check for vacuum leaks at throttle body, intake manifold, EGR valve or MAF sensor. Check for fuel contamination. Check for engine mechanical failure. Repair problem as necessary. After repairs, go to step 7). If problem is not found or repair was not necessary, diagnose fuel system. See SYSTEM/COMPONENT TESTS article.
- Inspect bank 2 for exhaust leaks, missing or loose hardware. Check if bank 2 HO2S is installed properly and if connectors are secured. Check vacuum leaks that will only affect bank 1. Check engine mechanical condition. Repair problem as necessary. After repairs, go to next step. If problem is not found or repair was not necessary, diagnose fuel system. See SYSTEM/COMPONENT TESTS article.
- Repair or replace affected faulty components. After repairs or replacement, 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 P0174. 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.