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.
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HOMESERVICE MANUALSOLDSMOBILE1998ACHIEVA 3.1 M, 4T40E/MN4REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 31 (ENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0453-P0656)DTC P0620DTC P0620: GENERATOR PERFORMANCEDIAGNOSTIC PROCEDURES
1998 Oldsmobile Achieva 3.1 M, 4T40E/MN4
Diagnostic Procedures
1998 Oldsmobile Achieva 3.1 M, 4T40E/MN4SECTION Diagnostic Procedures
WARNING: This page does not describe the selected car, but rather 65 other vehicles, including the 1999 Saturn SW2, 1999 Saturn SW1, 1999 Saturn SL2, 1999 Saturn SL1, and 1999 Saturn SL. However, it is still accessible from the selected car via links, so may be relevant.
- Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
- Start and operate engine at idle. Using scan tool, monitor generator. If scan tool indicates that generator is on, go to step 4. If scan tool does not indicate that generator is on, go to next step.
- Turn ignition off. Disconnect generator harness connector. Connect a DVOM between generator "L" terminal and a known-good ground. Start engine. Using scan tool, command generator on. Monitor voltage reading on DVOM. If voltage reading changes from zero to 5 volts, diagnose charging system. See appropriate STARTING & CHARGING SYSTEMS article. If voltage reading does not change from zero to 5 volts, go to next step.
- Check generator "L" circuit for open or short to ground. Repair as necessary. After repairs, go to step 8. If circuit is okay, go to next step.
- Check generator "L" circuit for short to voltage. Repair as necessary. After repairs, go to step 8. If circuit is okay, go to next step.
- Check for poor connection at PCM. Repair as necessary. After repairs, go to step 8. 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, review and record scan tool FAIL RECORDS data. Clear DTCs. Operate vehicle within conditions for setting this DTC. Recheck DTCs. If this DTC resets, go to step 2. If this DTC does not reset, 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.