Battery & Alternator Tips

Your Honda's engine will not turn over.
You put the key in the ignition, rotate it, and all you hear are clicking noises. The car does not start. These are strong indications that the battery system has failed. The engine's pistons and crankshaft will not start moving simply because air, fuel, and spark are present. Something has to initially "crank" the engine at a sufficiently high speed to compress the air and fuel mixture so a spark will ignite it. This something is the starter motor, driven by the battery. If the battery is not properly connected or is holding too low a charge (or maybe is flat-out dead), then the car will not start. First, check that the electrical cables connected to the two battery terminals are free of corrosion. Baking soda dissolved in water is an excellent cleaning solution for the terminals. Make sure the two clamps affixing the cables to the terminals are secure by tightening their respective bolts. Now use a multimeter to check the battery voltage. If the battery voltage is under 12 volts, then the battery is essentially dead and is not likely to start your car. Note that the battery might still have enough energy left in it to power your headlights, so a headlight check is not sufficient to identify a dead battery.

So your battery is dead. How did it get this way?
Batteries do wear with time, and yours may simply have reached the end of its useful life. If your battery is more than four years old, strongly consider replacing it. Alternatively, regardless of age, if your battery has been jump-started many times, replace it. The more times a battery has been permitted to empty its charge, the shorter its life will be. One internet site indicates the relationship is exponential. Suppose your battery is less than four years old, and you do not recall doing many jumpstarts on it. Then you need to consider whether the root of the problem here is the car's alternator. Your Honda has been starting, but the instrument panel's red warning lamp with the battery icon on it has also been lighting. Contrary to what the icon on the red warning lamp suggests, this lamp does not light when the battery charge is low. It lights when the alternator for some reason is not charging the battery properly. If this continues, your battery is likely losing charge and will need to be either replaced or recharged soon. But first, you need to determine why the alternator is not working correctly. Factory Service manuals offer in-depth diagnosis. These are available for many Hondas at the sites linked at Maintenance & Repair Resources. On the other hand, auto internet site and newsgroup reports suggest the most likely cause of alternator failure is worn brushes. To assist with a quick diagnosis, connect a multimeter's leads to the battery terminals; set the multimeter to "DC Voltage"; and perform the following voltage checks:

  1. With the engine off, should be at least 12 volts.
  2. With the engine idling over 1000 RPM (and so warming up), should be around 13.9 to 15.1 volts.
  3. With the engine idling and warmed up and the headlights, cabin blower, and defogger on, should drop below about 13.5 volts. If more loads need to be added to get the voltage to go below 13.5 volts, then this is fine.
  4. With the engine idling at a steady speed and so warmed up, voltage should not oscillate by more than maybe 0.1 volt. Oscillations of a full volt or more are a concern.
  5. Should never go over 16 volts.

If the alternator fails checks 1, 2, 3, or 4 , then the alternator's brushes might be worn, but there are other possible causes, too. If the alternator fails check 5, this suggests the alternator's voltage regulator is not working.

Brush failures are much more common than voltage regulator failures. Internet sites suggest brushes are likely to start failing after about 100k miles.

I strongly suspect the brushes. Can I replace them myself?
If you are handy or are an advanced beginner in your Honda repair experience, then yes, you probably can. Depending on the Honda year and model, you will either leave the alternator in place and unfasten the brush assembly, or you will have to remove the alternator in its entirety.

Maintenance & Repair Resources provides a link to a UK site that has factory service manuals for a number of Honda models. Several of these manuals have the steps for removing just the brush assembly. See also Alternator Brushes. To remove the alternator in its entirety, use any of the online Honda manuals (including Autozone's), supplemented by hints. Notice especially the hints about getting that extra inch or two of clearance needed to pull the alternator out: You will need to support and push against the engine via a jack, pressing against a block of wood, which presses against the oil pan. After this an engine mount is removed, and the engine is jacked higher. A similar method is used during timing belt removal, only the manuals are explicit about providing support at the oil pan.

Below is a drawing of a Denso alternator brush assembly. Click on the drawing to go to an alternator factory service manual site.

Here is a factory service manual drawing depicting a check of the Denso brushes' lengths:
Miscellaneous Notes:
  1. Other malfunctions that may cause the dashboard red warning lamp to light are a loose alternator belt, loose alternator cable connections, or bad bearings.
  2. Along with the red warning lamp, one may see other clues that the alternator system is amiss. For example, the headlights may dim intermittently while driving steadily and applying no additional electrical loads.
  3. Alternators were designed primarily to provide a "trickle charge" to a well-maintained battery. They are not supposed to routinely charge a near-dead battery to full charge. Commercial automotive sites are more emphatic about this: Avoid ever jumpstarting your car and then using your car's alternator to charge a dead battery. Charge the battery inside the house with a charger made for this job. Using the alternator to charge a near-dead battery is putting a strain on the alternator that will reduce its life.
  4. Discussion at suggests that a remanufactured alternator is one that has new bearings, new brushes, and maybe a new rectifier. If you remove your old alternator, check the bearings for play and consider replacing them.
  5. Many amateurs report that one can buy (very cheaply) alternator brushes at local electrical shops or hardware stores and put these into the brush holder of one's Honda alternator. But the consensus seems to be that buying the full, genuine Honda brush assembly is easier and guarantees the new brushes are secure in their holder.
  6. Many internet sites urge using only OEM parts for the alternator. Anecdotal reports are that aftermarket alternator parts do not last nearly as long.
My 91 Civic's alternator failed in 1999 at 106k miles. I did not know any better and took it to the dealer. The dealer installed a new alternator for $330. From my reading, this was likely more than was necessary. But remember, neither dealers nor customers like comebacks. Plus, the labor cost of an in-depth diagnosis might very well exceed the cost of just slapping a new alternator in place.
My 91 Civic LX uses a Nippon Denso alternator. The end cover (= the non-belt side cover) distinguishes it from the Mitsubishi alternator also used on this model. Benchmark data for my 1991 Civic LX, 1.5 year old, 75-month Interstate battery and alternator system, February 2006:
  • engine off voltage = 12.7 volts
  • engine idling, warming, over 1000 RPM voltage = 14.4 volts
  • engine idling, headlights, cabin blower, defogger on voltage = 13.5 volts

Battery log for 91 Civic:

  • July 1991-February 1996, Civic was driven in northern U.S. for about 95% of this time. The OEM battery had a few jumpstarts. Several days after a jumpstart, the OEM battery died enough so that it would not start the car. Charged it with old motorcycle battery charger and drove it to Sears. Replaced with Sears battery.
  • 1996-Sept 2000, northern U.S. driving continued. Civic was starting with difficulty over several days. Had a few jumpstarts. Checked voltage with all off: 10V. Replaced battery. New battery was not OEM. Poor starting ceased.
  • 2000-Sept 2004, about half the time in northern United States, rest in southern and southwest United States. Had one-to-a-few jumpstarts. Battery checked out fine, but decided to replace pre-emptively. New battery = Interstate.
  • 2004-present, driving in southwest United States. One jumpstart.
  • October 2008 voltage data: engine off = 12.5, idling = 14.3, idling with accessories on (see above) = 14.2.