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Phantom Headlights

Posted by suzie_ca (My Page) on
Sat, Mar 3, 07 at 15:54

2004 Jeep Grand Cherokee: headlights go off intermittantly while driving. . . stepping on break causes them to usually go back on. Had car to dealer 3 times -- can't find problem as it is intermittant and refuses to try any remedies until it malfunctions for them. Very scary on dark two lane roads.


Follow-Up Postings:

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RE: Phantom Headlights

had a s-10 that did that. turned out to be a bad headlight switch


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RE: Phantom Headlights

Unfortunately that's not much to go on. The way your headlights work is the switch sends a signal to the BCM (Body Computer Module) and the BCM closes the appropriate relay(s) to turn on the lamps. You did not specify if you have DRL's (Daytime running lights), or Fog lamps or not.

This could be something as strange as the BCM simply going to sleep on you while you are driving. Hitting the brake pedal at first look on the schematic does not seem to be directly involved except for possibly that since the brake lamp signal also goes to the ABS (Anti Lock Brake) module, the ABS module may be communicating on the PCI data bus and waking the BCM back up.

By chance does this seem to happen in a specific amount of driving time? Does there seem to be a related lapse in other operater inputs to the vehicle required for this to occur? Case in point. If you leave your headlights on and go into the house. Your car essentially recognizes that they are probably left on inadvertently and after ten to twenty minutes the car will shut the lamps off. Now whats really happening is that the BCM see's everthing else not communicating for a given period of time, and it goes to sleep turning the lamps off with it. If the details of when the problem occurs can be measured and then repeated, then the shop will have a better chance of catching the problem and diagnosing and solving it.

BTW the shop is correct in not just throwing parts at this in an attempt to fix it. This could be a corroded/breaking wire in almost any part of the circuit. Can you tell me what else happens? Does the dash go full brite like the car thinks it's daylight out? Or does the dash illumination remain where it's set? Does anything else stop working, or perform a reset? I realize when you suddenly find yourself driving at night without lights your concentration would be on trying to see where you are going, but if you can notice anything it just might be a clue that would allow you to re-create the failure during the day. Your automatic headlight sensor is at the top left of the dash. Try covering it with several layers of black electrical tape and get the headlights on during the day, and then drive and try to see if the system starts to act up, that will allow you to figure out what is actually letting the headlights come back on, just in case steppping on the brake isn't really turning them back on and they happen to just be coming back on themselves. But if as you say stepping on the brake does bring the headlights back, see if something else will, say like a power window switch, door lock switch, Heater/AC control, even a cruise conrol button. What I am looking for is to see if the system is reacting to a PCI data bus input or not when the lamps come back on.

What can make diagnostics like this difficult is that adding the scan tool to the car could keep the communication ocuring on the data bus and mask the problem while the tech has the car. Of course this may not be a data bus/BCM issue at all and simply something in the headlight circuit. If this helps and you do get the car to act up, call the shop and explain what you have done and that they are acting up right now. They will in all likelyhood have you bring it right in. If the do, do NOT shut the car off, or change anything. This will give the tech the best chance to see the problem continue.


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RE: Phantom Headlights

John_G has provided a great tip - Again!


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RE: Phantom Headlights

**BTW the shop is correct in not just throwing parts at this in an attempt to fix it. This could be a corroded/breaking wire in almost any part of the circuit.**

I agree with John g's entire post. This one sentence bugs me a bit though. What the shop is doing in this case is releasing the vehicle back to the owner for use in an unsafe condition. That's not a good thing. Assuming it was either new or still under warranty when the poster purchased it, this sounds like a safety issue and therefore a lemon law candidate to me.


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RE: Phantom Headlights

What other choice does the shop have Gary? Send an employee out at night to drive the car around and hope it acts up and he/she might then get to diagnose the problem? That could take weeks of driving the car, who pays for that? If the shop guesses and gets it right the problem is no one knows for certain that the car is fixed. So the driver ultimately gets in the car each time not knowing if this trip will be the one that the problem surfaces again. I can see it now, three years later the lights go out and "It's doing the same thing" If the shop throws a part at the car, and it's a wrong guess now they are open to litigation from just having to return the money for the failed attempted repair to the potential of damages due to potential vehicle damage/personal injury.

As far as lemon the law goes, now your putting the cost of this problem back onto the manufacturer, who ultimately must pass the cost back onto all of the other customers. This is difficult work, and there are no easy answers.


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RE: Phantom Headlights

**As far as lemon the law goes, now your putting the cost of this problem back onto the manufacturer,**

If this problem showed up under warranty, that's exactly where it should go. A manufacturer couldn't even legally sell a vehicle without functioning headlights along with host of other things. You John as an independent don't deal with warranty issues. From that perspective, you are 100% correct. A person brings in a car with any issue, if you can't confirm the complaint, you can't fix it. Not your car, you didn't sell it, buy it, or warranty it. Therefore it's not your problem, and you shouldn't make it your problem. If it's a warranty deal involving a safety issue, the manufacturer needs to fix it, replace it, or pay reasonable compensation.


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RE: Phantom Headlights

"who ultimately must pass the cost back onto all of the other customers"

The only warranty issues I have to deal with are when a repair that I perform fails within my warranty period, fortunately that is a very rare occurance. Although in a few cases legitamet work that I could have performed the first time has turned into warranty so the the customer takes the vehicle back to the dealer, and I lose the repair. The 150,000 mile, 15 year emission warranty wil be a significant burden for shops like mine to overcome. It's possible that warranty could thin the workload to the point that we may not survive as a business at all.


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RE: Phantom Headlights

**The 150,000 mile, 15 year emission warranty will be a significant burden for shops like mine to overcome. It's possible that warranty could thin the workload to the point that we may not survive as a business at all.**

Little bit off the defective safety equipment on a new car track, but the 150k 15 yr deal might not affect you at all. For one, I believe that's a California deal. Second, as long as I can remember emissions stuff has always had a significant warranty period. Don't know what specifically the legislation calls for, but if it's just an extension of what was covered in the past, it would only mean that things like the catalytic converter, air pump, and related sensors, modules, and valves would be covered. Filters, ignition parts, fuel system parts, mechanical failures such as vacuum leaks ect, wouldn't be covered even if the result of any of those problems was higher emissions. It wouldn't be a 15 year 150k bumper to bumper warranty. If people think they're going to get the car fixed for free under the emissions warranty every time there's a mis or the check engine light comes on, they're going to be in for a shock when they get the bill. Third, typical owners of 10+ year old cars don't have a lot of money to begin with and aren't likely to pay someone $$$ to repair a car now if it's running ok, check engine light or no. Those are my thoughts on the subject anyway.


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RE: Phantom Headlights

"Little bit off the defective safety equipment on a new car track, but the 150k 15 yr deal might not affect you at all."

It will affect us in a very significant way. I'll explain as we go point to point.

"For one, I believe that's a California deal.

Pa. has signed into law that we will follow California's lead.

"Second, as long as I can remember emissions stuff has always had a significant warranty period."

The advent of OBDII did have specific parts go for 8yr,80,000mile, specifically the convertor and the computer. They actually reduced the warranty period on some other components to help reduce the impact of this warranty on the aftermarket. The 15yr-150K makes no concessions and is a complete emissions warranty.

"Don't know what specifically the legislation calls for, but if it's just an extension of what was covered in the past, it would only mean that things like the catalytic converter, air pump, and related sensors, modules, and valves would be covered."

To work on todays cars completely, a shop like mine cannot get by with aftermarket scan tools. I have to buy the factory tools to have 100% vehicle coverage. The emissions warranty effectively cancels 60% to 70% of a tools usefullness by taking the bread and butter work the tool would be used for and making it now under warranty.

"Filters, ignition parts, fuel system parts, mechanical failures such as vacuum leaks ect, wouldn't be covered even if the result of any of those problems was higher emissions."

That's not correct. OBDII by design means if the vehicles emissions are impacted by a failure, it turns on the MIL, and it is an emissions failure which would be warrantable under the new regulation.

"It wouldn't be a 15 year 150k bumper to bumper warranty."

No but it's broad enough to make it prohibitive for me to buy the equipment to only be able to do the 30% to 40% of the work that would otherwise be avilable to me.

"If people think they're going to get the car fixed for free under the emissions warranty every time there's a mis or the check engine light comes on, they're going to be in for a shock when they get the bill."

Again, that's exactly the idea. The legislators feel that the best way to make sure the cars get fixed is force the manufactures to do it.

"Third, typical owners of 10+ year old cars don't have a lot of money to begin with and aren't likely to pay someone $$$ to repair a car now if it's running ok, check engine light or no."

But if they could get if for free they would, and that's the argument used by the legislators in support of the warranty.


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RE: Phantom Headlights

**No but it's broad enough to make it prohibitive for me to buy the equipment to only be able to do the 30% to 40% of the work that would otherwise be avilable to me.**

If you're trying to be a one man show, I don't know how you do it now without specializing. Most mechanics who don't own the business have their own hand and air tools, that's about it. Diagnostic tools, machine tools, cutting and welding equipment, current shop manuals, ect, are usually purchased by the shop and are shared by everyone working there. Pretty hard for an individual to purchase all that stuff and use it enough to make it worth buying in the first place. Probably always was.

Have to wait and see on that California deal. I have a hard time believing even they would try to require warranty repair for normal maintainence/wear items, including mechanical failures that would result in conditions that would simply overwelm the emissions system.


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RE: Phantom Headlights

man i would think the private garage and mechanic would almost be a lost thing. in this day of leases and 100k warrantys. the guy i used to go to 20 yrs ago, has moved into the aftermarket parts installation gig. says the profits higher and the frustration level is lower puttin a lift kit on a jeep, compaired to tuning one up. all he does now suspension kits, brake kits etc etc.


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RE: Phantom Headlights

Jumping in late, and "half-cocked" ( I suppose) but I assume the 100K Mile warranty doesn't cover everything, just the main running gear (engine/transmission/differential), there should still be a lot of work for independent garages: brakes, clutch, alternators, starters, gee someone stop me.

I have run my past three cars over 100K and one to 200K and the only work I had done at any shop (dealer or independent) that I paid for was "stuff" that I'm pretty sure isn't covered by the new 100K warranties. If the cars are not strong enough to go the distance without major repairs the dealers/mfgs would go broke fixing them. Warranties are written to cover stuff that lasts longer, in most cases, than the warranty.

Hi John G, I haven't visited this forum for a while, and it is good to see you're still giving a lot of valuable inputs.


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