Car won't start...alternator or starter?

Question

My car will not start. A month ago it wouldn't start. At that time it was still cranking (weakly) but not starting. I bought a new battery and installed it. It still wouldn't start until I jumped it (which doesn't make sense since it's a new battery) and then it started. I took the old battery back and the worker said that the battery was fine. Keep in mind this was all a month ago and it was running fine until now.

It stopped starting up again. I did notice that the starts were getting weaker just before it stopped starting again. This time I had to get it towed. Now it will not crank at all and makes a single click and nothing more. Is this indicative of a bad starter or a bad alternator or is there something else I'm missing? All my electronics still seem to work fine, it just won't start so I'm leaning more towards the starter.

Vehicle is: 2006 Honda Civic EX 1.8L 4 Cylinder (though it shouldn't matter).

I did do a search and could not find any questions with this specific case.

UPDATE: I put in a fully charged battery (battery tested good and was charged using a battery charger) and it would not start. Like I mentioned before, a month ago it did crank (weakly) and wouldn't start. Now it doesn't crank at all and just clicks. Is this solely a problem with the starter or could this be indicative of an underlying problem?

UPDATE 2: It was the starter. It was going bad and would fail when it got hot.

Answer 1

To differentiate between the starter and the alternator you can check the battery voltage – should be about 12.6 with the engine off and 13.5-14.2 with the engine running if the alternator is doing its job.

You may have a failing starter. You can get a good take on this by taking a current reading while trying to start. Usually this is done with a specialized meter, so you may want to take it to a motor shop or a car parts store and ask them to test it. A failing motor will usually have a very high draw (or none).

However, if the car won't move… The starter should cause a large drop in battery voltage when it runs (and even more if it doesn't run, but is trying to). So if you have access to a volt meter you could also try reading the voltage before and during an attempt to start. Any significant drop in voltage indicates that the motor is trying to run. If it isn't then I'd say it's time to take the motor in for repair/replacement.

Answer 2

There's a potential third posibility, which is the positive battery cable to the starter.

In order to evaluate this, you should perform what is called a voltage drop test on the cable, using a voltmeter connected between the positive battery post, and the major cable lug on the starter.

Observe the voltage while an assistant cranks the starter. The battery does NOT have to be fully charged. Anything more than 0.4 volts displayed is an indication that this cable, or it's connections have developed a high resistance. That's voltage that went "missing" over the trip of the copper cable. It's corroded or failed to the point it can't conduct high starter currents without loss.

What's more, is this effect may not be consistent... it might vary considerably with outside temperature, or how many/how often the vehicle has been started recently. The resistance in such main cables increases with temperature.

Be sure to repeat this test with the battery ground cable or strap, as it can fail the same way. (Voltmeter between battery negative post and the metal starter frame.)

So:

@dlu advice is excellent; this will help decide if your altenator is charging your battery. Given your substitution of other charged batteries, I think the problem lies elsewhere.

"My" test will eliminate or identify the main starter cable as the problem, which although seeming silly, is actually quite common.

The only thing left at that point will be the starter.

Answer 3

If you're hearing a click, it's likely that the starter circuit is receiving electrical current, but a mechanical component inside the starter itself has failed (i.e. starting motor, solenoid etc). Since your car isn't starting, your alternator can't help maintain battery charge, and your constant attempts to start the car, likely with the accessories on, continue to drain your battery.