1. Alternator Issues: This is the most probable cause. A failing alternator can't charge the battery adequately. This leads to:
* Battery Light: The light indicates low charging voltage.
* Check Engine Light: The PCM (Powertrain Control Module) detects the low voltage and sets a code.
* No Start: The battery is drained from insufficient charging. The car may crank slowly or not at all.
2. Battery Problems: Even if the alternator *is* working, a weak or failing battery can cause similar symptoms. Age (20 years old) is a significant factor here.
* Battery Light: A weak battery can't maintain voltage under load, triggering the light.
* Check Engine Light: Low voltage affects the PCM, possibly setting a code.
* No Start: An insufficiently charged battery simply won't provide enough power to crank the engine.
3. Wiring Issues: Corrosion, loose connections, or damaged wiring in the charging system (between the battery, alternator, and starter) can interrupt the flow of electricity. This can mimic alternator or battery problems.
4. PCM (Powertrain Control Module) Problems: Although less likely to directly cause the no-start, a faulty PCM can send incorrect signals related to charging and ignition, leading to the lights and failure to start. This is less probable than the other causes unless there are other electrical gremlins.
5. Starter Motor Issues: While a bad starter motor primarily prevents cranking, a partially faulty one could draw excessive current, depleting the battery and triggering the lights. This is more likely to show a slow crank rather than no crank at all.
Diagnosis Steps:
1. Battery Voltage Test: Check the battery voltage with a multimeter. A fully charged battery should read around 12.6 volts. A lower reading indicates a weak battery.
2. Alternator Voltage Test: With the engine running, check the alternator voltage. It should be between 13.5 and 14.5 volts. Lower voltage indicates a failing alternator.
3. Visual Inspection: Examine the battery terminals, alternator belts, and wiring for corrosion, loose connections, or damage.
4. Check Engine Code Retrieval: Use an OBD-II scanner to retrieve any stored diagnostic trouble codes (DTCs). These codes provide valuable clues about the problem.
5. Starter Test (if cranking is weak): Have a mechanic test the starter for proper operation.
In summary: The most likely scenario is a failing alternator or a weak battery, possibly exacerbated by worn wiring. Start with the simpler and less expensive tests (battery voltage and visual inspection) before moving on to more involved diagnostics like alternator testing and code retrieval. A professional mechanic can quickly diagnose the issue with the right tools and experience. Ignoring the problem could lead to being stranded with a completely dead battery.
