#304639 - 02/12/2007 06:28
Low beams keep burning out.
|
carpal tunnel
Registered: 20/12/1999
Posts: 31600
Loc: Seattle, WA
|
Before I call CarTalk, I'd like some brainstorming ideas.
- 1995 Oldsmobile Achieva owned by Vixy.
- Car *HAS* been taken to the local Olds dealership in an attempt to solve the problem, they just replace the burned out bulbs and don't find anything else wrong.
- Bulbs keep burning out extremely fast. Prior times it took on the order of weeks or a couple of months. But the last time, both bulbs stopped working almost immediately: Replaced bulbs, they worked long enough to look and see that they were working, then the car was moved into and out of a driveway the next day, then when we went to move it back into the driveway the third day, both bulbs were burned out again. No long-term use, and bam, they're bad again.
- Ruled out general case of bad bulbs, because they are burning out simultaneously each time. And this has gone through multiple repeats of the issue, with different amounts of time between each one.
- Bulbs are halogens. They are the kind where you have both the low and the high beam contained within the same actual bulb itself. When you look at the bulbs in a cursory fashion, they don't look particularly bad. But when you look very close, you can see the difference between the highbeam filament which looks fine, and the low beam filament which looks blobby and slightly melty (but not blackend per se).
- Vixy thinks but cannot confirm for sure that the lowbeam burnouts are somehow related to the highbeam usage. For example, they worked fine for a few months until she turned on the high beams and then she noticed they were out. However she can't be sure; she concedes that the last time she might have turned on the high beams because the low beam bulbs were already burned out and she was just trying to make it brighter.
- High beams always work fine and do not burn out. Only the low beam filaments in the same bulbs burn out.
- Clearly there is some kind of an electrical problem, but where to start looking? There are perfectly good fuses in the proper places and of the proper ratings.
Ideas?
Diagnostic questions and tests welcomed: Between me and Vixy, we'll try them out and perhaps narrow down the issue.
|
|
Top
|
|
|
|
|
#304640 - 02/12/2007 08:27
Re: Low beams keep burning out.
[Re: tfabris]
|
addict
Registered: 25/06/2002
Posts: 456
|
I wonder if one of the fuses, though of the proper rating, is a defective fuse or perhaps installed in such a way that something is shorting across the terminals. Though, if that is the case, it just means that you'll be blowing fuses all the time instead of headlights. Albeit cheaper, though equally annoying. Do you have access to a shop manual or wiring diagram of the car? I wonder if there is some sort of transformer or voltage converter feeding the headlight circuit -- though I'm fairly certain sealed beam Halogens run off straight 12V DC. Another thought is that a flaky alternator could be injecting noise spikes into the system that wouldn't trigger a slow blow fuse. Have you checked the Empeg FAQ entry about tracking down grounding problems?  Maybe an iffy contact in the headlight switch or somewhere in the wiring harness could be causing the lights to jiggle on-and-off rapidly enough that the light remains fairly constant but you get a lot of on/off transients through the filament while driving. If all else fails, maybe you could install tonyc's old breaker panel in series with your fusebox....
|
|
Top
|
|
|
|
|
#304641 - 02/12/2007 11:56
Re: Low beams keep burning out.
[Re: tfabris]
|
carpal tunnel
Registered: 29/08/2000
Posts: 14494
Loc: Canada
|
Bad/blown voltage regulator. Fortunately, that should be a simple user-replaceable part. Check the vehicle manual to find out for sure. EDIT: Hmmm.. it seems that many places overprice the regulator,
in hope that you'll just buy an entire new/refurb. alternator instead
(the regulator is usually located inside the alternator).
/EDITCheers
Edited by mlord (02/12/2007 12:13)
|
|
Top
|
|
|
|
|
#304642 - 02/12/2007 12:36
Re: Low beams keep burning out.
[Re: tfabris]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
I'm thinking this probably isn't a voltage problem. Car electrical system vary from 12 to 15 volts when operating, but volts high enough to kill the headlights would be killing other things as well.
On GM stuff, the headlights are protected by an "automatic resetting circuit breaker". I'm betting this breaker is old and corroded.
Have you tried an ohm measurement of the low beam filiment after removing the bulb? See if it's really dead, or you're just replacing bulbs while the breaker resets...
Also, connect a volt meter to the headlight socket and rev the motor. I'll bet the volts don't go over 15, but if they do, then it's the voltage regulator.
|
|
Top
|
|
|
|
|
#304643 - 02/12/2007 12:43
Re: Low beams keep burning out.
[Re: larry818]
|
carpal tunnel
Registered: 29/08/2000
Posts: 14494
Loc: Canada
|
Quote:
On GM stuff, the headlights are protected by an "automatic resetting circuit breaker". I'm betting this breaker is old and corroded.
If it were that, then high-beams wouldn't work either. But they do work.
|
|
Top
|
|
|
|
|
#304644 - 02/12/2007 12:46
Re: Low beams keep burning out.
[Re: mlord]
|
carpal tunnel
Registered: 29/08/2000
Posts: 14494
Loc: Canada
|
Quote:
Bad/blown voltage regulator.
Fortunately, that should be a simple user-replaceable part.
Check the vehicle manual to find out for sure.
EDIT: Hmmm.. it seems that many places overprice the regulator,
in hope that you'll just buy an entire new/refurb. alternator instead
(the regulator is usually located inside the alternator).
/EDIT
Cheers
Note that if the shop claims no problem, it could be a flakey thing -- where the regulator works until it hits a certain temperature or load, and then just shorts out and blows the (sensitive) halogen lamps.
An empeg would be safe, though, as it is tolerant of higher voltages (to a point).
Cheers
Edited by mlord (02/12/2007 12:46)
|
|
Top
|
|
|
|
|
#304645 - 02/12/2007 13:38
Re: Low beams keep burning out.
[Re: mlord]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Quote:
If it were that, then high-beams wouldn't work either. But they do work.
For whatever reason, the high beams are fused and lows are on a breaker.
I'll try and find a schematic on this...
I thought it was telling that the low beams burn out together... and don't look burned out when removed.
Monitoring the voltage would be useful.
Are you getting all the replacement bulbs at the same source?
|
|
Top
|
|
|
|
|
#304646 - 02/12/2007 13:49
Re: Low beams keep burning out.
[Re: larry818]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Quote:
I'll try and find a schematic on this...
I didn't find anything linkable. My '81 malibu was this way, but I did find a schematic for an '87 that was just fused.
It should be a simple thing to measure the voltage at the low beams when they are not working...
|
|
Top
|
|
|
|
|
#304647 - 02/12/2007 14:16
Re: Low beams keep burning out.
[Re: tfabris]
|
carpal tunnel
Registered: 29/08/2000
Posts: 14494
Loc: Canada
|
Quote:
- Bulbs are halogens. They are the kind where you have both the low and the high beam contained within the same actual bulb itself. When you look at the bulbs in a cursory fashion, they don't look particularly bad. But when you look very close, you can see the difference between the highbeam filament which looks fine, and the low beam filament which looks blobby and slightly melty (but not blackend per se).
Tony, dig out an ohm metre and check for continuity across the low beam filament.
(can one do this with halogen bulbs?)
If it's really burned out, there shouldn't be any conductance there at all.
-ml
|
|
Top
|
|
|
|
|
#304648 - 02/12/2007 14:26
Re: Low beams keep burning out.
[Re: mlord]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Quote:
Tony, dig out an ohm metre and check for continuity across the low beam filament.
(can one do this with halogen bulbs?)
Yes, halogens are just incandescent bulbs filled with a halogen gas rather than argon.
http://en.wikipedia.org/wiki/Halogen_bulb
You're probably thinking of the HID lights.
|
|
Top
|
|
|
|
|
#304649 - 02/12/2007 14:43
Re: Low beams keep burning out.
[Re: mlord]
|
old hand
Registered: 20/07/1999
Posts: 1102
Loc: UK
|
A couple of thoughts occur. 1) Vibration in conjunction with bad contacts. I had a car where the spring clamp mechanism that holds the base of the bulb (which is the earth) in place was worn and weak. The result was that when you drove the car, especially if you went over a bump, the bulb would bounce in the socket and momentarily flicker. After a remarkably short time, the low beam filament would burn out! It never affected the high beam. I put it down to current spikes combined with the vibration mechanically stressing the thinner filament. 2) One or more faulty diodes in the alternator. Alternators are three-phase AC generators, diode rectified to a not particularly clean DC. If one of the diodes goes out, you will get a fairly high voltage AC signal superimposed on the the nominally 12V DC line. A scope will show it instantly, a meter set to AC may well show it as an AC component to the DC voltage. If you can measure frequency with the meter, you'll see it change with engine RPM. As Mark says, if the voltage regulator in the alternator was bad you may well also get more than 12-15v out. This would make the current going through a specific resistance, ie. a bulb, increase proportionately. The high beam filament may be man enough to take it, the low beam probably wouldn't. However, I suspect you'd also have all sorts of problems with other things working oddly/not working/smoking as well. Such as tail light bulbs, interior lights, etc. Note that a bad diode in the alternator would kill the regulator fairly fast as well, so we might both be right  At least in the UK, the regulator and diode pack are integrated into the alternator. It's easier and cheaper to replace the whole thing. If it is a bad alternator, eventually it will eat the battery as well. pca
_________________________
Experience is what you get just after it would have helped...
|
|
Top
|
|
|
|
|
#304650 - 02/12/2007 16:29
Re: Low beams keep burning out.
[Re: tfabris]
|
carpal tunnel
Registered: 25/12/2000
Posts: 16706
Loc: Raleigh, NC US
|
I would say that the obvious first step would be to check the voltages at the headlight receptacles. Both low beam and high beam with the car set to low beam and high beam and during the change in each direction. While you're there, you might want to make sure there's not a short in the connectors, so try measuring impedance between the high and low beam contacts with the power off.
_________________________
Bitt Faulk
|
|
Top
|
|
|
|
|
#304651 - 02/12/2007 16:37
Re: Low beams keep burning out.
[Re: wfaulk]
|
carpal tunnel
Registered: 29/08/2000
Posts: 14494
Loc: Canada
|
Quote:
I would say that the obvious first step would be to check the voltages at the headlight receptacles.
I suspect that may be somewhat tricky to achieve at 55MPH. 
But the lighter socket inside the cabin should show pretty much the same voltage as anywhere else.
Cheers
|
|
Top
|
|
|
|
|
#304652 - 02/12/2007 17:47
Re: Low beams keep burning out.
[Re: larry818]
|
carpal tunnel
Registered: 20/12/1999
Posts: 31600
Loc: Seattle, WA
|
Quote:
For whatever reason, the high beams are fused and lows are on a breaker.
VERY interesting.
These are all good suggestions here, I'm going to try the things you're mentioning. Thanks, everyone, I'll report back.
|
|
Top
|
|
|
|
|
#304653 - 02/12/2007 17:52
Re: Low beams keep burning out.
[Re: tfabris]
|
enthusiast
Registered: 31/05/2002
Posts: 352
Loc: santa cruz,ca
|
if the bulb is really burned out, over voltage is the most likely cause.
no fuse wrong or faulty will cause this.
a short that causes another consumer to pull power through the bulbs, making the bulbs act as fuses is possible, but not very likely at all.
if the cause is over voltage, the regulator may not be at fault, but should be suspect.
the test-
with engine off, switch on lamps to make sure they're still working.
connect volt meter to bulbs (either side, but use the ground point at the bulbs for meter hook up), you should see something like 11.x volts with the bulbs on and the engine off.
start engine and rev to ~2,000 rpm.
load the electrical system by switching on things like the A/C, power windows, sound system, anything that requires a fair amount of juice.
I expect your charging system to operate within 13.2 - 13.8 volts. pushing 15 volts is not cool. in fact, at 15 volts I would say you have a problem.
if you do find higher than comfortable voltage start checking --
-voltage drop from alternator case to ground points at 1)battery negative post, 2)bare metal of engine and 3)any gang connection on the frame. half a volt (1/2) is the highest you wanna see in any case.
-as silly as it may sound, really make sure your battery connections are perfect (1/10 drop while cranking motor)
-if the alternator is mounted to the engine via vibration dampners, check the hell out of the alternator-to-engine ground strap. twice.
-check the smaller wires connected to the alternator, you should see a black plug on the rear/side of the alternator. with the engine off, remove this connector and make sure it's in good shape. a poor connection here will trick the regulator into an over charging state.
if you do find higher than normal voltage, the regulator may be the fault, but keep in mind that it's not that hard to trick a regulator into thinking it needs to go mad on the field winding in order to do its job.
there should be no more than 1/2 volt drop from the large lead on the back of the alternator (B+) to the center of the positive post on the battery with the engine running a good load on the system.
this all assumes the bulbs are realy burning out. the fact that they seem to die at the exact same time (left and right) is a little odd.but lets assume you know power is present at the bulbs when they're not working. (both the positive and negative side)
in 20 years of working on cars full time, over voltage is the only cause I have ever witnessed myself.
a few thoughts-
use 'Osram' bulbs, and never touch the glass to anything, including your fingers.
do not use high wattage bulbs (45-55 watts is normal)
make sure there is no after market alarm or fog lamps that may be wired in.
|
|
Top
|
|
|
|
|
#304654 - 02/12/2007 22:14
Re: Low beams keep burning out.
[Re: mlord]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Quote:
I suspect that may be somewhat tricky to achieve at 55MPH.
I guess I should have been more clear. Assuming the bulbs are still out when stopped, check to see if there's any voltage at all. That would indicate if something is amiss with the breaker (if any).
But yeah, the cig lighter port would tell you if you're over voltage at speed.
|
|
Top
|
|
|
|
|
#304655 - 02/12/2007 22:18
Re: Low beams keep burning out.
[Re: lastdan]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Quote:
use 'Osram' bulbs
I wanted to mention this too. At one time I got a few cheap chinese bulbs that would only last a couple of weeks. The Osrams live forever.
Quote:
do not use high wattage bulbs (45-55 watts is normal)
Thanks to the HID lights others are sporting, I've got 100/140 watt halogens in my car, just so I can maybe see what I'm about to hit...
Stock wiring is holding up to it.
|
|
Top
|
|
|
|
|
#304656 - 02/12/2007 22:31
Re: Low beams keep burning out.
[Re: larry818]
|
old hand
Registered: 16/02/2002
Posts: 867
Loc: Oxford, UK
|
Quote:
use 'Osram' bulbs
I researched this a couple of years ago and Osram Silverstar quartz halogen were highly rated. I didn't notice any drastic difference when I fitted some myself though. Be warned though, some websites offering these bulbs use HID 'after' photos.
Quote:
Thanks to the HID lights others are sporting, I've got 100/140 watt halogens in my car, just so I can maybe see what I'm about to hit...
Don't be left in the dark, you can get HID conversion kits fairly cheaply nowadays. I've been using an H7 bulb replacement kit on dip beam for 18 months now (bought from eBay/HK) and I wouldn't go back. Local legislations may prohibit this where you live, and I've also seen a lot of naysayers scaremonger folks away from installing these kits - check with your vehicle testing station. I made a point of mentioning the upgrade at my car's annual vehicle test (MOT) and the tester didn't have any objections.
|
|
Top
|
|
|
|
|
#304657 - 02/12/2007 22:44
Re: Low beams keep burning out.
[Re: AndrewT]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Quote:
Don't be left in the dark, you can get HID conversion kits fairly cheaply nowadays. I've been using an H7 bulb replacement kit on dip beam for 18 months now (bought from eBay/HK) and I wouldn't go back. Local legislations may prohibit this where you live, and I've also seen a lot of naysayers scaremonger folks away from installing these kits - check with your vehicle testing station. I made a point of mentioning the upgrade at my car's annual vehicle test (MOT) and the tester didn't have any objections.
Thankfully there's no inspection here (although there should be everywhere), so no trouble that way.
Unfortunately, my car has the dual beam bulbs, and there's a real lack of good info on dual beam HID lights. Most offer bulbs that don't move, so you lose high beam. Others it seem one can't be sure of what you're getting...
I did convert from the 2004 light to H4, so it seems converting to HID *should* be easy...
|
|
Top
|
|
|
|
#304658 - 03/12/2007 01:19
Re: Low beams keep burning out.
[Re: larry818]
|
carpal tunnel
Registered: 29/08/2000
Posts: 14494
Loc: Canada
|
Quote:
Thanks to the HID lights others are sporting, I've got 100/140 watt halogens in my car, just so I can maybe see what I'm about to hit..
What's HID ?
EDIT: Never mind..
Edited by mlord (03/12/2007 01:21)
|
|
Top
|
|
|
|
|
#304659 - 03/12/2007 01:56
Re: Low beams keep burning out.
[Re: tfabris]
|
carpal tunnel
Registered: 17/12/2000
Posts: 2665
Loc: Manteca, California
|
_________________________
Glenn
|
|
Top
|
|
|
|
|
#304660 - 03/12/2007 04:07
Re: Low beams keep burning out.
[Re: gbeer]
|
carpal tunnel
Registered: 20/12/1999
Posts: 31600
Loc: Seattle, WA
|
Thanks, Gbeer, those are useful schematics.
|
|
Top
|
|
|
|
|
#304661 - 04/12/2007 14:45
Re: Low beams keep burning out.
[Re: tfabris]
|
carpal tunnel
Registered: 20/12/1999
Posts: 31600
Loc: Seattle, WA
|
Although recent tricky weather in the area has kept us from going outside to work on the car, I do have updated diagnostic information: - The car's turn signals have recently been known to blink slowly. This is intermittent. - The power windows have been known to go up and down slowly. This is also intermittent. Combined with the other reported symptoms, what does this indicate? Voltage regulator?
|
|
Top
|
|
|
|
|
#304662 - 05/12/2007 04:49
Re: Low beams keep burning out.
[Re: larry818]
|
carpal tunnel
Registered: 20/12/1999
Posts: 31600
Loc: Seattle, WA
|
Quote:
Also, connect a volt meter to the headlight socket and rev the motor. I'll bet the volts don't go over 15, but if they do, then it's the voltage regulator.
Motor off: 12 volts.
Motor starting: 15 volts, peaking slightly higher, like 15.2 or so.
Motor idling: 14.5 volts.
Motor revving: 14.7 volts.
Does that mean anything bad, or does it mean a normally operating vehicle?
All of the above was with vehicle working normally on all axes. For instance, the turn signals worked at normal speed.
Oddly, the lights are working right now. When we moved the car the other night and the lights didn't work, we *assumed* they'd burned out again, but they don't seem to have done so. It was a very cold day, and snowing, maybe that was a factor.
Do any of these data points help?
|
|
Top
|
|
|
|
|
#304663 - 05/12/2007 06:22
Re: Low beams keep burning out.
[Re: tfabris]
|
enthusiast
Registered: 31/05/2002
Posts: 352
Loc: santa cruz,ca
|
Quote:
Do any of these data points help?
yes.
I think we can all agree the bulbs are not failing (:
http://gkb.servehttp.com/images/achevia/sch2.gif
as this image shows, both positive and ground are switched.
it would really be a good idea to find out which goes missing.
that's easy to do at the bulb.
does that car have Day Running Lights?
when the lows fail, what happens when you switch the main switch off?
seems like there's a good chance the breaker is just doing it's thing, maybe it's too sensitive, or maybe it's functioning as it should, protecting the circuit. but before you even bark up that tree, you should verify that power goes missing at the bulb on the hot side, if that's the case check to see if power is going in and out of the breaker. seems like you could just bypass it with a 20 amp fuse.
I would expect slightly lower voltage readings from your test, but if it's really cold and the test was done soon after starting the engine, it's not that far off.
|
|
Top
|
|
|
|
|
#304664 - 05/12/2007 10:25
Re: Low beams keep burning out.
[Re: tfabris]
|
old hand
Registered: 01/10/2002
Posts: 1039
Loc: Fullerton, Calif.
|
Yes, these data points indicate that the charging system is fine. Motor starting should have been 10 or 11 volts, but no biggie. Since the lights are resetting, it's gotta be an automatic breaker somewhere. Here is what it should look like: http://www.aquavolt.com.au/persistent/catalogue_images/categories_thumb/225010.jpgHunt it down and replace. The slow blinkers / windows is probably an unrelated problem. And we americans have the nerve to call Lucas the prince of darkness...
|
|
Top
|
|
|
|
|
#304665 - 05/12/2007 19:33
Re: Low beams keep burning out.
[Re: lastdan]
|
carpal tunnel
Registered: 20/12/1999
Posts: 31600
Loc: Seattle, WA
|
Quote:
I think we can all agree the bulbs are not failing (:
Well, actually, they definitely are failing, at a much higher rate than they otherwise should, it's just that this *last* time they hadn't actually failed.
Quote:
does that car have Day Running Lights?
No.
Quote:
when the lows fail, what happens when you switch the main switch off?
Define "Main Switch". Do you mean the main headlight on/off switch? And what do you mean "What happens"? Well all the lights on the car turn off like they're supposed to. What else would you expect to happen?
Quote:
seems like there's a good chance the breaker is just doing it's thing, maybe it's too sensitive, or maybe it's functioning as it should, protecting the circuit.
I'm thinking the same thing.
Doug Burnside wanted to post here with a detailed reasoning of something, but the BBS ate his post again. But he thinks there's an "open" in the hibeam/lobeam switch that is triggering that circuit breaker.
This gels with an additional statement Vixy has made (oh hey, I mentioned it earlier in the thread): Sometimes she thinks the *act* of using the hibeams is the thing that makes the lobeams fail. This didn't make any sense to me until now. But in theory, a short in the hi/low switch could easily cause that circuit breaker to pop, couldn't it?
I think our next course of action is to replace the hibeam/lobeam switch as Doug suggested.
Everyone concur?
My only concern: How much trouble is this, and does it involve working around the airbag? Is this something I can do in an evening?
|
|
Top
|
|
|
|
|
#304667 - 05/12/2007 20:57
Re: Low beams keep burning out.
[Re: tfabris]
|
enthusiast
Registered: 31/05/2002
Posts: 352
Loc: santa cruz,ca
|
>>Everyone concur?<<
with all due respect, I do not.
while it may well be the case, it may well not be.
I did mean the standard head lamp switch, and asked about the DRLs because it can help narrow things down. the DRLs work when the switch is off, so had they come on when you switched them off we would have known more about the power path... but if the car doesn't have them, it doesn't matter.
maybe I've become confused, but did you say the the first sets of bulbs that didn't work were confirmed to have 'blown out'?
working with the air bag is not that hard. to be safe, disconnect the battery first, and then make sure everything is plugged in before you hook it back up, this way it should not log any trouble codes in the SRS (airbag system).
I would bypass the breaker with a standard fuse, 20 amp.
if it snaps, you can always hook the breaker up again, but at least you have a record that a short/high load did occur.
the next time you catch them not working, unplug both bulbs and check for power at either one (tan wire at bulb for low beam).
if power is there, plug one bulb back in and check again.
if the reading drops out, check voltage drop across the switch and the breaker.
I just printed out the diagram for the "SC" model and it looks nothing like the diagram posted above. what variant is that car?
>>Well, actually, they definitely are failing, at a much higher rate than they otherwise should, it's just that this *last* time they hadn't actually failed.<<
this is the part that confuses me.
if the bulbs are actually cooking, it's not an issue with any breaker, switch, or short. you just can't kill bulbs that way.
|
|
Top
|
|
|
|
|
#304668 - 05/12/2007 22:09
Re: Low beams keep burning out.
[Re: tfabris]
|
old hand
Registered: 16/02/2002
Posts: 867
Loc: Oxford, UK
|
I can't help but think that the bulb filaments are failing because either: a) They are burning out due to an overvoltage situation. - or - b) An intermittent connection is [thermally] stressing them. For a) I'm still unconvinced that we've been able to rule out an intermittent voltage regulator at the alternator. I'd imagine the increased brightness of the lamps would probably go unnoticed while driving on busy roads with streetlighting. The dashboard lights might give a clue but OTOH, they are quite likely to be PWM driven and therefore less susceptible to voltage fluctuations. Have you had an OBD [etc] diagnostic reading taken? Taken from here, there are a number of helpful fault codes that the ECU might have snagged: Code:
P0560 System Voltage Malfunction
P0561 System Voltage Unstable
P0563 System Voltage High
Some ECUs reset the stored fault codes after a number of ignition cycles and others keep then in a pseudo FIFO buffer where new codes displace old ones. Depending upon how yours works you may have 12yr old codes stored so you will need to get the codes read/reset, go away and blow some bulbs then return for a fresh reading. I also have another hypothetical scenario: Lets say there is something inductive on the car's 12v supply, e.g. a suppressor choke, wiper motor or a blower motor. If there's a faulty (intermittent) feed to that inductor, when the power breaks there will be a back EMF when the magnetic field collapses around the inductor that will send a negative spike back onto the 12v supply. I appreciate this theory sounds a bit far fetched. I just wanted to get you thinking about (or looking for) things like big suppressor chokes, perhaps aftermarket ones the previous owner fitted to prevent 'thumps' killing speakers when the headlamps (etc) were switched on?
|
|
Top
|
|
|
|
|
|
Previous Topic
Index