Hyundai Repair: my sonata dies on me, voltage drop test, starter solenoid

Question
I've had a problem with my 2002 sonata not starting. I've taken it to the shop three times. First they thought it was the starter so they replaced it. The second time they though it was safety switch so they screwed it tighter so it would connect with the starter wire I guess. The third time they believed it was still the safety switch but fix it. Each time after I've gotten the sonata from the garage it fails to start the next day when I try to start it after having parked at a business running errands. I've had to have it towed twice. Now it's at a dealers and they couldn't find anything wrong with it. They drove around and it ran fine. The same thing happened the last time I took the sonata to the garage. It ran fine for the them but it dies on me the day after I get it back from the shop. What's the problem?

Answer
Hi, Quentin.  Unfortunately, I cannot tell you what the problem is because it can still be a significant number of things.  If we presume that the starter doesn't crank the engine when the problem occurs (since that would be the symptom if the components replaced had been the issue), we can probably safely assume this is an electrical issue of some sort.

The next step is to perform some checks while the problem is occurring.  If the problem is not occurring at the time the tests are made, all tests will return good results.

1.  What is the battery voltage when attempting to crank the engine?  Less than 10V indicates the battery is at least partially discharged and the cause will need to be investigated.  If there's nothing draining the battery it'll need to be replaced.  Less than 6V indicates the state of the battery is likely causing your issue.

2.  Perform a voltage drop test on each of the battery cables when with the headlamps on.  A voltage of more than 0.1V indicates the cable should be replaced.  More than 6V indicates the cable being tested is likely the source of the issue.

3.  Check the along the starter solenoid circuit when attempting to crank to see where proper voltage is present.  If you have proper voltage at the starter solenoid and lug, and you've verified the condition of the cables, then that leaves only a starter issue.


I've lumped some things together above without many specifics because I expect the shop will be making these tests-- they should know how to perform them and should have the information available to diagnose the circuits.  If you're going to attempt some tests yourself, follow up with what you plan on doing and request the specific additional information you'll need.  As long as you'll be sending the car back to the shop when the condition occurs again, plan on leaving the car at the shop until they can replicate the condition and make some meaningful tests.  If then cannot duplicate the problem, it'll be nearly impossible for them to guess the correct repair.