SCFriend

My friend with a 2007 SC430 has been having weird electrical issues for the past few years. He's owned the car about 6 years now, and probably 3 or 4 years ago things seem to have started acting up:
- the car burns out headlight and foglight bulbs very often, usually after less than a year since they are replaced. It hasn't mattered if the replacements he tries are OEM Lexus or aftermarket, they burn out within a year or so - sometimes within only a few months. He previously owned a 2002 SC430 for about 4 years and never had to replace any bulbs. On the 07, it's usually always one of the driver's side bulbs that will go first, and then within a month or two the passenger's side goes. Sometimes a headlight goes, then the foglight on the same or opposite side goes. Other times a fog goes out and a short time later the headlight on that side goes out.
- his driver's seat heated seat stopped working earlier last year. First the "bottom" stopped working, then a few weeks later the "back" section stopped too. Lexus diagnosed blown heating elements, which can't be replaced without replacing the entire section of the seat. So he found a complete seat from a wrecker and swapped it in. Everything worked fine for about 3 months, and now he is back to no heated seat again (this time both the back and bottom sections stopped working at the same time)

A Lexus dealer spent 4 hours "diagnosing" the car and came back saying all electrical systems are normal, so they can't say why the bulbs are always burning out or why two different seats have stopped working. The car is getting up there in mileage (closing in on 200K miles) but has always been properly maintained.

Retroplay

I know Lexus says everything checks out fine, but this spells out large voltage spikes to me. Perhaps it is intermittent and they just haven't caught it yet.

I would pick up a voltage meter that plugs in to the cigarette lighter socket and keep an eye on it, especially during car starting.

Plugs in to the cigarette lighter:
http://www.ebay.com/itm/12V-24V-Moto...9UtOqg&vxp=mtr

A better method to do long term datalogging (recommended) that wouldn't cost too much is by using an OBD scanner and a laptop with software capable of datalogging. You would set it up to record the voltage it reads from the OBD port. The Toyota techstream cable and software can do this, I believe.

If you find spikes, I would look at replacing the alternator. There might be spots in the coil where it is shorting out.

In the meantime, a question:

Has your friend ever noticed the lights getting brighter/dimmer while driving?

Harold57

+1 on what Retroplay said.

There is definitely a voltage problem somewhere in the system. Bad diodes in the alternator or a sick regulator, bad spots in the coil (like Retroplay said) or bad/dirty/loose/corroded connections to the battery or alternator.

Have him tune into a weak AM station and listen for the type of noise. Sometimes that can narrow down the culprit also. Listen for pops or general noise that changes with engine speed.

Any chance that this car has been in a flood?

SCFriend

I will ask about the dimming/brightening

We did take the car for a drive with a cheap little DMM connected on the cigarette lighter socket, there weren't any spikes but there were some split second "dips" dropping to down to like the +10V range. One issue of course could be that some spikes/dips can happen too quickly for a digital meter to catch them, which is where you really need an oscilloscope to see what's going on. I guess it stands to reason that if there are dips happening (that the meter we used was able to catch) there could very well be spikes occurring as well.

SCFriend

No dimming/brightening that he has noticed. Typically just before a headlight burns out, he has seen some "flickering" from the dying bulb which Lexus told him is normal behavior for a bulb on its way out just before it's toast.

Retroplay

Yeah, my first recommendation was an Oscope, but I know many people don't have one or know how to use it. If you do and can, definitely recommended.

However, an Oscope just measures voltage over time, so a real datalogger (not the OBD kind) with a high enough sample rate should catch it.

An analog meter (with a dial) would be better than the digital, if those are impossible.

The dips might be a concern, but most likely not what you are looking for. That's well within the range of operation and the voltage will vary a bit based on the load on the engine such as the A/C compressor coming on.

The spikes would need to be pretty fast to prevent a fuse from blowing. You are right, a digital meter probably wouldn't catch it unless you were lucky.