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Odd problems fixed - speedometer, odometer, ABS, weird headlights, no start, more!

Discussion in 'Under the Hood' started by NewOrgnlDave, July 12, 2011.

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    1. NewOrgnlDave

      NewOrgnlDave New Member

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      You may have some or all of these symptoms, and the early and later ones may be intermittent:

      EARLY SYMPTOMS
      • headlights dim when accessories and especially both power windows are in use at the same time
      • the odometer stops working, speedometer is odd
      • rough shifting sometimes but not others under the same conditions (acceleration, temperature, etc.)

      LATER SYMPTOMS
      • sporadic ABS problems
      • speedometer stops working altogether
      • stalls
      • transmission may enter 'limp mode' and shift VERY HARD only to be fine when you turn the car off and on again

      DEAD SYMPTOMS
      • It appears the alternator has gone bad, both when tested and when driving
      • Car won't start
      • Erratic behavior of electric systems

      I had my electrical system fail yesterday; the truck wouldn't start. But it was odd.

      Oftentimes you start with trying to figure out whether it is the battery or the alternator causing the trouble.

      The standard test seems to be, use a volt meter to look at the voltage across the terminals of the battery when the car is off, then start it (even if it requires a jump start) and test it again. If the voltage rises, your battery is broken and won't charge anymore, if the voltage stays the same or dips, your alternator is having problems, be it the wiring or the regulator or the alternator itself.

      For me, with my truck off, the voltage was fine, like the battery was 100% charged, but it dipped VERY SIGNIFICANTLY, maybe below 11V, after it was jump-started. Like I said above usually this means alternator problems.

      But before you rush off to troubleshoot your alternator, possibly spending a lot of time and money by replacing it only to have the symptoms continue, read this.

      After it was jumped, no accessories could be used - just the lights (it was dark out). I actually had to pull the A/C clutch solenoid fuses and stereo fuse so they wouldn't draw any power just to get around. Otherwise my truck would stall out or start having hard clunks with erratic RPMs and the ABS light would flash briefly but repeatedly, and the clock on the radio along with it (before I pulled those fuses). The car worked much better when I went over 35mph. The speedometer would fluctuate around 14mph when I was stopped, or stay at 35mph; when I went over 35mph it would work fine and there would be much less problems. My battery didn't charge at all, not even a little.

      Very strange behavior happened when I tested it the standard way. I tried pulling every fuse one after another to see if there ws a 'leech' - a component that had short circuited and was drawing all the power. The dome light stayed on constantly and wouldn't turn off no matter what I did except for one fuse; I had to pull it out, but while I was testing the fuses (before I pulled it) it fluctuated (got brighter and dimmer and went off sometimes) a lot, and could have been a big help if I knew what I was looking for better. Anyway. Turning the key to the spot just before the ignition - when all the lights on the dash are on and you can turn on the blower, etc. (when your car is in good condition), maybe 80% of the time nothing would happen or the dash lights would come alive. When you tried a larger load - the vent fan (blower), the stereo, or the lights, usually - the voltage across the battery terminals would immediately plummit to <5 and the power would cut out. Then when you turned the lights or whatever system you tried would turn off, and there would be either a little or a LOT of clicking as relays reset themselves.

      But the other 20% of the time, you could run one or MAYBE two of those systems fine. The blower would blow for minutes on end, or the lights would turn on (dimly), or the stereo would play, louder than I was comfortable with. The voltage would drop but not as much. I still couldn't start it of course.

      That was odd, I thought. A dead battery is a dead battery. Why could it draw amperage sometimes and not others?

      A car battery usually has 6 'cells.' Each cell is a smaller battery, and they are chained together in series; if one has a problem, it effects all the others. And you can get a battery with a slightly defective cell that has passed QA testing at the factory without even knowing it.

      You may remember back in highschool or middle school, your science teacher lit up a small light bulb by sticking leads into a potato. But if he tried two lightbulbs, they would go out. This is because the potato has a (relatively) high VOLTAGE, but cannot supply very much AMPERAGE. It has a lot of electric PULL, but not much electric SUPPLY. When the SUPPLY was exceeded, all of the sudden it couldn't have much PULL anymore, because there was nothing there.

      This is why you test your battery's charge by reading a precise value when the car is off; with more amperage available (energy stored), the voltage (energy pull) will be higher. In my case my battery read 100% charged.


      As a side note the voltage is read by drawing a very, VERY insignificant current.

      When your car is on, your battery is technically a load on the alternator - the alternator is doing all the electrical work, including charging the battery. The battery acts like any other load, such as power windows, your A/C, headlights, etc. But that faulty cell has strange chemistry. Sometimes it will place a larger load on the alternator, as the alternator tries to charge the broken cell; sometimes the chemistry will change and it will be fine. The bad times, it will cause minor undervoltage to several systems that are sensitive to it, such as ABS, speedometer, etc. As it gets worse, you *may* get later symptoms, such as stalls, etc, as the battery sucks up more and more of the voltage, dipping it below what the running components require.

      However, usually it will just fail. And when it fails, you'll get that inconsistent behavior I had - as you keep applying loads to it, the chemistry in the cell will change, sometimes allowing a small current through it, sometimes not allowing any. When it is jump-started it will have a very low voltage like your alternator is on its last legs and it will have a LOT of problems driving.

      If you are having any of the symptoms and can't troubleshoot them, or especially if your electrical system fails, I urge you to test for a faulty battery cell. If the car is running, a good way to do this is to put both power windows all the way up, and keep holding the buttons, and look at the headlights. They would dim noticeably, because the alternator is struggling to charge the battery correctly AND put out enough power for other things. This can also be an early sign of alternator failure too, though, so it doesn't rules the alternator out.

      But when it dies, check the battery as I did. It will probably read 100% charged, but be unable to carry *any* load 80% of the time, and 20% of the time the lights will work. When jump started it will have a lot of problems and the voltage will be very low.

      I didn't know all this for sure until I replaced my battery, it was mostly a theory based on the erratic behavior. With all this supposition in my head, I went against conventional wisdom (diagnose the alternator) and just called AAA. I didn't have a ride for a battery and they have great battery service here. They came, tested the battery, found out it was putting out 0 amps sometimes and ~.5 other times. The alternator checked out fine, so they replaced the battery and wala, the truck is doing better than before, all the symptoms are gone, it is even shifting smoother (after it re-learned how to shift, of course), the alternator is working great, speedometer/odometer/etc., all fixed!

      You can test this pretty easily, even at the early stages, without spending ANY money if you have a friend who's willing to let you 'borrow' their battery for just a few minutes (take the proper precautions of course!!!)

      And all against conventional wisdom that told me it should be the alternator I should go after. I don't even know how much time, energy, and money I saved by figuring this out, and I wanted to share it with you all as you have shared with and helped me.
       
      Last edited: July 12, 2011
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    3. albi1cnobi1

      albi1cnobi1 Elite Mountaineer Elite Explorer

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      You're right on with the potato battery analogy. Your battery is probably good, but if it is not being charged it wont last long with the accessories on. There are 3 possible causes. The 1st being a bad alternator. 2nd a bad cable. And 3rd being the mega fuse next to the power distribution box. If that fuse is bad the alternator gets no B+ and cannot generate a charge.
       
    4. NewOrgnlDave

      NewOrgnlDave New Member

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      I'm sorry, I don't know if I didn't make myself clear, or if you didn't read the whole thing. I'll reiterate that it turned out that despite the fact that all signs pointed toward my alternator, as you pointed out, it was my battery that was damaged. The alternator is in tip-top condition, putting out great voltage/current, despite having just over 160k miles on the truck.
       
    5. albi1cnobi1

      albi1cnobi1 Elite Mountaineer Elite Explorer

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      Sorry, guess I missed that.
       
    6. matt0248

      matt0248 Active Member

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      A bad cell in a battery will do what you describe, look good, 12.6V when no load is on the battery. That is why the best way to test a battery is a load test, drawing significant amps from the battery to see if it can handle the load. My guess is that if you had the battery load tested that you would have come to the same conclusion of a bad battery. just maybe sooner.
       

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