Ghosts in the machine

Today a college professor of mine was talking about his Hyundai Sonata and telling us how last night when it was really cold out (2 degrees Fahrenheit) he parked his car at a restaurant and shut it off only to realize that he’d left the blower fan still set on high, so he switched it off after the car had been shut off.

Later, when he restarted the vehicle, the blower as well as the headlights were nonfunctional. He had the car towed home and then this morning everything works fine. The dealership’s explanation, which I think is bogus, is that there was dust in the sensor that activates the automatic headlights, but there’s no way that should affect the blower or affect turning on the headlights manual (he tried switching them on).

Anyone here have any ideas as to what may have caused this?

I would guess that there is a sticky relay somewhere. Cold can make some relays get sticky. It should not, normally, but it can happen. Without seeing a schematic of that particular car it would be hard to tell which relay(s) to suspect. I doubt switching the fan switch off had any effect.

I vote “relay” also. The blower switch is not energized with the engine off. Dust in the sensor is way, way out in left field.

What year of car and how many miles?
It’s quite possible for an auto lamp module to screw up and fail to turn the lighting off.
(It happened to me one time on my old Lincoln Mark about 6 or 7 years ago. Went into a restuarant one evening, assumed the lights would turn off on their own, they didn’t, and I came out to a badly run down battery. So much for turning your back on electronics.)

However, in this case when the car was restarted the blower and lamps were not working. In my opinion this could point to a failing fuse or a heavier duty fuse link. Not having a wiring diagram for this car and not being terribly familiar with Hyundais, I’m guessing the car has an underhood fuse/relay box that should contain the heavy duty stuff.

Many of these fuse links have a clear plastic cover through which a small wire element can be seen. Over time it so happens that the solder used on high current applications such as blower motors and lighting may soften and even melt a bit due to current heat. This in turn can cause an intermittent fault in the electrical circuit. Often, a tiny solder flaw can be seen with the naked eye through the clear cover.

Was this car presented to the dealer as a warranty repair and the warrany status of the concern was denied and placed into the “customer pay” field? Then you recieved a basic diagnostic charge and told the problem was “dust on the sensor”? If I have the senario correct the Dealer did not find a cause for the headlight issue and did not want to start the clock running on a repair they know may end up with a buy back. since they have not acknowledged a problem the clock is not running but I do think there is an issue with the electrical system.

This is a “pay the bill presented” situation and keep a record of it, when the problem happens again you will have grounds to request the basic diagnostic fee you were charged be returned.

A search by you for Technical Service Bulletins related to this problem on the same year vehicle or previous year vechicles (even different models of Hyundai’s) may get you in the Prof’s good graces, espically if you find one.

My professor didn’t reveal the year or mileage so I don’t have that information. I was just asking this question out of my own curiosity being an auto enthusiast who really had no idea what could be causing it.

He said he just called and asked them what they thought might have caused it, I don’t know the year or mileage but the way he talked about it I got the feeling it’s not a brand new Hyundai so I doubt it was warranty related. I am going to try and find some technical service bulletins both because of my own interest and because I might get the chance to help him out.