* Weak Starter Motor: The starter motor's brushes are likely worn down, the commutator is pitted, or the windings are failing. This explains the slow cranking initially, and now the complete failure to turn over. The solenoid is clicking because it's engaging, but the motor itself lacks the power to turn the engine.
* Bad Battery Connections: Loose, corroded, or damaged battery terminals or cables can prevent sufficient current from reaching the starter. Check the terminals for corrosion (clean them with a wire brush and baking soda if needed) and ensure they are tightly connected. Also, inspect the cables for damage (breaks in the insulation, fraying, etc.).
* Failing Battery: While less likely given the initial slow cranking, a weak battery might not have enough juice to overcome the increased resistance from a failing starter motor. Test the battery voltage with a multimeter.
* Solenoid Issues (Less Likely): Although the solenoid is clicking, it might be failing internally. This is less probable given that it's likely engaging, just not providing sufficient power. It's still worth investigating if other components check out.
* Wiring Problems: There could be a broken or damaged wire in the circuit between the battery, solenoid, and starter. Inspect all wiring carefully for breaks or corrosion.
Troubleshooting Steps:
1. Check Battery Voltage: Use a multimeter to test the battery voltage. It should be around 12.6 volts when fully charged. A low voltage indicates a weak battery.
2. Inspect Battery Cables and Terminals: Clean and tighten all connections at the battery, starter, and solenoid.
3. Tap the Starter: Carefully tap the starter motor with a hammer or wrench (while someone tries to crank the engine). If it starts, it's almost certainly a failing starter motor. Caution: Do this with the battery disconnected for safety.
4. Test the Starter Motor (Advanced): This requires removing the starter and testing its voltage and current draw. A multimeter and some electrical knowledge are needed for this step.
5. Inspect Wiring: Carefully examine all wiring related to the starter motor and solenoid. Look for any broken or damaged wires.
In most cases, a worn-out starter motor is the culprit given the progression of symptoms. Replacing the starter is likely the most effective solution. It's best to have this diagnosis and repair performed by a qualified mechanic if you lack the experience or tools to diagnose and repair electrical systems.
