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Thread: Rear Lamp Failure

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    Registered 97JGCLimited's Avatar
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    Default Rear Lamp Failure

    I have a 97 Grand Cherokee Limited with the VIC that displays warning messages. Whenever my key is in the accessory position, I get the rear lamp failure message on the VIC. Whenever the key is in the run position, I do not get the message though. I have checked all my lights many times including the 3rd brake light. I want to know what the problem is and what would make the message come up when the Jeep isn't running and not come up when it is. I do not know if this is related or not, but whenever my lights are on, my blinker blinks really fast sometimes.

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    Thats a turn signal or a relay,, go around with ur turn signals on and see what lights are flashing so that you know where all the bulbs are,, Then when its flashing really fast go around and check to make sure all the bulbs are flashing, but dont jump out if ur going down the hw to check them,he. If they are check the relay,, lol sorry i have no clue where this is but ur om should tell you.. I hate that when it flashes really fast..

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    It looks really trashy and like I don't take care of my Jeep. I have checked every bulb with the lights on and off. I even went as far as to take it to the dealership. They had no clue. All they could tell me was possibly a bad ground somewhere.

  4. #4

    Default Re: Rear Lamp Failure

    -=- originally posted by 97JGCLimited -=-
    I have checked all my lights many times including the 3rd brake light. I want to know what the problem is and what would make the message come up when the Jeep isn't running and not come up when it is. I do not know if this is related or not, but whenever my lights are on, my blinker blinks really fast sometimes.
    You have 3 bulbs in that "third" brake light. Even 1 burned out will activate the VIC warning.

    For a fast blinking turn signal ... that's a turn-signal light is burned out someplace or a bad relay. Check the side marker on the front of the ZJ ... you have 4, 2 on each side. Some flash with the signal, though they should be off when the blinker blinks on. One being burned out shouldn't cause the turn signal thing, but check anyway. Then check the signal bulbs in all 4 corners. Also, make sure you have the corect Wattage lights in place ... change any bulbs recently? And lastly check the ground conections - that could also cause problems.
    like my name says:
    97 ZJ - it's green

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    After some research last night, I read a post somewhere about the same problem. It turns out the bulbs send a certain voltage back to the computer and if the voltage is wrong(if you buy a bulb other than from the dealership)the computer gets the wrong voltage sent back to it. I replaced the relay today for on that handles a variety of voltages. It was a Tridon Stant EP27 relay from Autozone. They tried to give me the wrong thing at first as usual but I eventually found it. After installing the new relay, I turned on the lights and turned on the blinker. It didn't blink fast. It has blinked fast for the past 2 years. I hope it continues to work right.

  6. #6

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    -=- originally posted by 97JGCLimited -=-
    After some research last night, I read a post somewhere about the same problem. It turns out the bulbs send a certain voltage back to the computer and if the voltage is wrong(if you buy a bulb other than from the dealership)the computer gets the wrong voltage sent back to it. I replaced the relay today for on that handles a variety of voltages. It was a Tridon Stant EP27 relay from Autozone. They tried to give me the wrong thing at first as usual but I eventually found it. After installing the new relay, I turned on the lights and turned on the blinker. It didn't blink fast. It has blinked fast for the past 2 years. I hope it continues to work right.
    You are talking about the turn signal bulb. Yes, unfortunately that specific bul type (the 1295NA) is only carried by dealers. It is actually no longer in production, from what I hear. Maybe a specialty store might stock them ... but that's a long shot.

    One thing to note ... the 1156NA typically found in autoparts stores doesn't just draw fewer amps (it's that lower amp draw the the BCM senses ... a burned out draws none, and the 1156NA still draws too few) it is also has 35% lower light output.

    You could always by the bulb at the dealer if you want to keep the 50 candlepower output. Or you could do the turn-signal lamp mod. There are three write-ups here.
    like my name says:
    97 ZJ - it's green

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    Default Re: Re: Rear Lamp Failure

    -=- originally posted by 97greenZJ -=-
    You have 3 bulbs in that "third" brake light. Even 1 burned out will activate the VIC warning.
    Is that the case for a 95 also, I am having the same error, but I only saw 2 bulbs in there, maybe I need to look harder.

  8. #8

    Default Re: Re: Re: Rear Lamp Failure

    -=- originally posted by dnorton -=-
    Is that the case for a 95 also, I am having the same error, but I only saw 2 bulbs in there, maybe I need to look harder.
    My understadning ... for all the good that is ... is that at some point they switched the ZJ from a single-bulb CHMSL to a three bulb version ... there was never a "two-bulb" version.

    So ... putting 2 and 2 together I'd venture to guess that one of your 3 bulbs is out. It's pretty painless to check ... just unscrew the trim pieces, pull them off, and remove the brake light assy.

    BTW, when you buy the replacement bulb, there is one that's brighter (a higher cadlepower output). I upgraded all 3 bulbs while I was in there. It's my sincere hope that slightly brigter bulbs will draw better attention to the fat green ass of the ZJ looming larger and larger in the windshields of any idiots following too close. If that doesn't, my trailer hitch will.

    I'll try to dig up the p/n of the bulb that I used.
    like my name says:
    97 ZJ - it's green

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    I still get the warning rear lamp failure on my VIC when the key is in the accessory position. When the key is in the run position, I don't get the warning. Anybody have any thoughts about that one?

  10. #10

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    my best guess ...

    When you have the key in the acc. position you are getting battery voltage throughtout the system ...say 12 V or so. Remeber resistanced is constant so at that voltage, amerage draw is lower than when the engine is running and the alternator is kicking out 14.4 - 14.8 V. (I=V/R ... incrase V and you increase I.)

    Since The VBCM senses current draw/voltage drop it can see that the total resistance of the system. If the resistance is higher than spec, current draw will be too low across the circuit. The resistance might be borderline ... OK when the extra voltage from the charging system is applied, making the BCD happy (and thus the VIC does not display the error) - and not OK when the voltage is below threshold ... running of battery with the key in the acc position.

    It's just a theory, but it would explain the behavior.
    like my name says:
    97 ZJ - it's green

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    It is the best explanation I have heard of so far. Do you know of any fix for the problem? I guess I could look at every bulb in the back of the Jeep and find the ones that are not the ones that put off the certain voltage that the computer likes, but that doesn't seem worthwhile. Is there another relay or something I could change out like I did with the flasher relay? I have also read somewhere about a lamp outage module that could be the problem.

  12. #12

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    The Rear Lamp Failure message appears when either a brake lamp or tail lamp goes out. Turn signals and back-up lights aren't included in the circuit, IIRC. That means there should be 5 bulbs involved: the three 922 bulbs in the CHMSL and the two 3057 buls, one in each of the tail lights.

    The VIC resets itself on every start up ... so the warning should not fire off until you step on the brake pedal (as you would when you go to put the ZJ into gear) if the problem is a brake light. Similarly, the warning should not fire off until you turn on the lights and the rear tail lights try to light up. That's waht happened on mine - again, if I'm remembering things correctly.

    One problem I did have once was when the VIC would fire off that message when all my bulbs were working. That time the problem turned out to be a problem with my external harness for the trailer lights mounted on the hitch frame. Everything had gotton corroded in the salt air (I was living at the beach in FL then). My solution, correct of not, was to whack the wires off the harness, restrip them and reattach to a new one.

    As an aside ...

    I replaced the 922's in my CHMSL with 921K (LL) bulbs - the one's that are spec'd for the ZG (the European version of the ZJ). The 922's produce 15cp while the 921's produce 21cp. Replacing all three and the CHMSL produces 63 vs. 45 candlepower! In addition, they are Krypton filled and are rated at 1,800 hours instead of the 200 hour rating for the stock bulbs. Translation ... you'll never have to replace them again.

    I replaced my 3057's with 2357K (LL) bulbs - also spec'd for the ZG. The 3157's produce 3cp while the 3057 produce 2cp ... that a 50% increase in the light output for your tail lights! Both bulbs put out 40cp when the brake pedal is pressed. Again, these are Krypton filled and will last ~10,000 hours - twice the life of the stock bulbs.

    <rant>
    Why is it that the Euro Grands got better lighting all around: real glass headlamps with much better optics (less glare, more light on the road), brighter headlight bulbs, leveling/aiming switch inside the vehicle, and better bulbs in just about every location??
    </rant>

    So, if you're going to open up all those bulb locations to have a look-see, you may want to look at making those lighting upgrades.

    BTW, the rear turn signals and back-up bulbs are also 3057's, IIRC. I did not upgrade those yet; I'm actually looking into something even brighter for the back-up bulbs.

    For comparison purposes here's he Wattage, Amperage, and Voltage of the bulbs:

    Bulb number.....CP......Hours....Amps.....Design Volts

    922................15.......200......0.98......... .12.8
    921................21......1000......1.4.......... ..12.8
    921K (LL)........21......1800......1.4............12.8

    3057..............32......1200......2.1........... .12.8 - brake pedal depressed
    ..................... 2......5000......0.48..........14.0 - stop light, continuos on
    3357..............40.......400......2.23.......... 12.8 - brake
    ..................... 3......5000......0.59..........14.0 - stop
    3357K (LL)......40.......800......2.23.........12.8 - brake
    ..................... 3....10000......0.59..........14.0 - stop

    Note: These specs are for genuine Osram-Sylvania bulbs. Other brands will use the industry standard bulb number ... but may or may not have the same output or wattage.

    Why do Krypton filled bulbs last longer? The short explanation is that the pressure of the inert gas prevents molecules of tungsten from evaporating off of the filamnet surface as quickly as they do in non-filled bulbs, keeping the filament intact longer.
    like my name says:
    97 ZJ - it's green

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    Thanks for the info on the bulbs. The warning message doesn't come on when I press the brakes or turn on the lights, only when the key is in the accessory position. I wonder if replacing the bulbs would cause the message to go away. I am also going to check my trailer wiring harness for corrosion. I am also going to check into the lamp outage module. I think it is located in the side compartment in the rear hatch on the left.

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