Owner's Problem Description
The owner reports that when attempting to start the car, the ignition turns on but the starter only clicks once, and the interior lights dim. After replacing the battery and testing the starter (which passed), the issue persists. The starter clicks but the engine does not turn over, suggesting a possible electrical issue or engine lock-up.
Professional Technical Analysis
The 1989 Cadillac Fleetwood FWD, equipped with a 4.5L V8 engine and approximately 120,000 miles, exhibits a starting issue characterized by a single click from the starter when the ignition is turned on. This symptom often points to an insufficient power supply to the starter motor. Given the replaced battery, it indicates either a poor connection or a high resistance in the starting circuit. The dimming of interior lights suggests that the battery is under load or that there is a significant voltage drop when attempting to engage the starter. An essential first step is to inspect the battery connections, ensuring they are clean, tight, and free from corrosion. Additionally, the integrity of the starter relay and the ignition switch should be evaluated. Checking the voltage at the starter terminal while attempting to crank the engine can reveal if adequate power is reaching the starter. If the power supply is confirmed but the starter still does not engage, a mechanical failure within the starter or the engine could be suspected. The mechanic's diagnosis of a locked AC compressor should be verified; removing the drive belt temporarily can determine if the engine is seized. These complex interrelations highlight the importance of methodical testing to isolate the fault effectively.
Possible Causes
Most common causes (ordered by frequency):
- Poor battery connection or high resistance in the starting circuit: Despite a new battery installation, loose or corroded connections can lead to insufficient voltage reaching the starter, causing a single click and dimming lights. Battery terminals should be cleaned and tightened to ensure optimal contact. Voltage at the starter should be tested during crank attempt, ideally above 10V. - Dim interior lights during start attempt, voltage drop observed at the starter terminal, corrosion at battery terminals.
- Starter motor internal failure: While the starter passed a bench test, it may still have internal faults such as worn brushes or a damaged solenoid. This can prevent the starter from engaging even when power is supplied. - Single click from the starter, no rotation of the engine, normal voltage supply at starter terminal.
- Engine seizure or mechanical failure: The mechanic’s observation of a locked AC compressor implies potential engine lock-up, which needs to be verified. A seized engine will prevent the starter from turning, indicating a severe mechanical issue. - Resistance felt when manually attempting to turn the engine, AC compressor unable to rotate.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Battery Inspection: Begin by inspecting the battery terminals for corrosion and ensuring they are tight. Use a digital voltmeter to measure the battery voltage; it should read above 12.4V. If the battery is good, proceed to check the voltage at the starter terminal while attempting to crank the engine. It should remain above 10V during cranking for proper operation.
- STEP 2 - Starter Voltage Testing: With the ignition on, measure the voltage at the starter solenoid terminal while a helper turns the key to the start position. If voltage is present but the starter does not engage, further investigation into the starter's internal components is warranted. If no voltage is present, trace back to the ignition switch and starter relay.
- STEP 3 - Mechanical Inspection: If the electrical components test out well, check for engine seizure. Remove the drive belt and manually attempt to turn the crankshaft using a socket on the crankshaft bolt. If the engine turns freely, the issue is likely electrical; if it does not, a mechanical failure is indicated.
