GM S10/S15/Sonoma Pick-Ups 1982-1993 Repair Manual




All batteries, regardless of type, should be carefully secured by a battery hold-down device. If this is not done, the battery terminals or casing may crack from stress applied to the battery during vehicle operation. A battery which is not secured may allow acid to leak out, making it discharge faster; such leaking corrosive acid can also eat away components under the hood. A battery that is not sealed must be checked periodically for electrolyte level. You cannot add water to a sealed maintenance-free battery (though not all maintenance-free batteries are sealed), but a sealed battery must also be checked for proper electrolyte level as indicated by the color of the built-in hydrometer "eye.''

Keep the top of the battery clean, as a film of dirt can completely discharge a battery that is not used for long periods. A solution of baking soda and water may be used for cleaning, but be careful to flush this off with clear water. DO NOT let any of the solution into the filler holes. Baking soda neutralizes battery acid and will de-activate a battery cell.

Always use caution when working on or near the battery. Never allow a tool to bridge the gap between the negative and positive battery terminals. Also, be careful not to allow a tool to provide a ground between the positive cable/terminal and any metal component on the vehicle. Either of these conditions will cause a short circuit leading to sparks and possible personal injury.

Batteries in vehicles which are not operated on a regular basis can fall victim to parasitic loads (small current drains which are constantly drawing current from the battery). Normal parasitic loads may drain a battery on a vehicle that is in storage and not used for 6-8 weeks. Vehicles that have additional accessories such as a cellular phone, an alarm system or other devices that increase parasitic load may discharge a battery sooner. If the vehicle is to be stored for 6-8 weeks in a secure area and the alarm system, if present, is not necessary, the negative battery cable should be disconnected at the onset of storage to protect the battery charge.

Remember that constantly discharging and recharging will shorten battery life. Take care not to allow a battery to be needlessly discharged.


See Figures 1, 2 and 3

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Fig. Fig. 1: On non-maintenance free batteries, the level can be checked through the case on translucent batteries; the cell caps must be removed on other models

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Fig. Fig. 2: Check the specific gravity of the battery's electrolyte with a hydrometer

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Fig. Fig. 3: A typical sealed (maintenance-free) battery with a built-in hydrometer-NOTE that the hydrometer eye may vary between battery manufacturers; always refer to the battery's label

Battery electrolyte contains sulfuric acid. If you should splash any on your skin or in your eyes, flush the affected area with plenty of clear water. If it lands in your eyes, get medical help immediately.

The fluid (sulfuric acid solution) contained in the battery cells will tell you many things about the condition of the battery. Because the cell plates must be kept submerged below the fluid level in order to operate, maintaining the fluid level is extremely important. And, because the specific gravity of the acid is an indication of electrical charge, testing the fluid can be an aid in determining if the battery must be replaced. A battery in a vehicle with a properly operating charging system should require little maintenance, but careful, periodic inspection should reveal problems before they leave you stranded.

Fluid Level

Check the battery electrolyte level at least once a month, or more often in hot weather or during periods of extended vehicle operation. On non-sealed batteries, the level can be checked either through the case on translucent batteries or by removing the cell caps on opaque-cased types. The electrolyte level in each cell should be kept filled to the split ring inside each cell, or the line marked on the outside of the case.

If the level is low, add only distilled water through the opening until the level is correct. Each cell is separate from the others, so each must be checked and filled individually. Distilled water should be used, because the chemicals and minerals found in most drinking water are harmful to the battery and could significantly shorten its life.

If water is added in freezing weather, the vehicle should be driven several miles to allow the water to mix with the electrolyte. Otherwise, the battery could freeze.

Although some maintenance-free batteries have removable cell caps for access to the electrolyte, the electrolyte condition and level on all sealed maintenance-free batteries must be checked using the built-in hydrometer "eye.'' The exact type of eye varies between battery manufacturers, but most apply a sticker to the battery itself explaining the possible readings. When in doubt, refer to the battery manufacturer's instructions to interpret battery condition using the built-in hydrometer.

Although the readings from built-in hydrometers found in sealed batteries may vary, a green eye usually indicates a properly charged battery with sufficient fluid level. A dark eye is normally an indicator of a battery with sufficient fluid, but one which may be low in charge. And a light or yellow eye is usually an indication that electrolyte supply has dropped below the necessary level for battery (and hydrometer) operation. In this last case, sealed batteries with an insufficient electrolyte level must usually be discarded.

Specific Gravity

As stated earlier, the specific gravity of a battery's electrolyte level can be used as an indication of battery charge. At least once a year, check the specific gravity of the battery. It should be between 1.20 and 1.26 on the gravity scale. Most auto supply stores carry a variety of inexpensive battery testing hydrometers. These can be used on any non-sealed battery to test the specific gravity in each cell.

The battery testing hydrometer has a squeeze bulb at one end and a nozzle at the other. Battery electrolyte is sucked into the hydrometer until the float is lifted from its seat. The specific gravity is then read by noting the position of the float. If gravity is low in one or more cells, the battery should be slowly charged and checked again to see if the gravity has come up. Generally, if after charging, the specific gravity between any two cells varies more than 50 points (0.50), the battery should be replaced as it can no longer produce sufficient voltage to guarantee proper operation.

On sealed batteries, the built-in hydrometer is the only way of checking specific gravity. Again, check with your battery's manufacturer for proper interpretation of its built-in hydrometer readings.


See Figure 4

The sealed top battery cannot be checked for charge by checking the specific gravity using a hand-held hydrometer since there is no provision for access to the electrolyte. Instead, the built-in hydrometer must be used in order to determine the current state of charge:

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Fig. Fig. 4: Sealed maintenance free batteries contain a built-in hydrometer to help determine battery charge

  1. If the indicator eye on top of the battery is dark, the battery contains sufficient fluid. If the eye is light, the electrolyte fluid is too low and the battery must be replaced.
  3. If a green dot appears in the middle of the dark eye, the battery is sufficiently charged. Proceed to Step 4. If no green dot is visible, charge the battery as in Step 3.

Do not charge the battery for more than 50 amp/hours. If the green dot appears, or if electrolyte squirts out of the vent hole, stop the charge and proceed to Step 4.

  1. Charge the battery referring according to the proper charging rate (amps) for the necessary time span and rate of charge.

    75 amps-40 min
    50 amps-1 hr
    25 amps-2 hr
    10 amps-5 hr


It may be necessary to tip the battery from side-to-side to get the green dot to appear after charging.

When charging the battery, the electrical system and control unit can be quickly damaged by improper connections, high output battery chargers or incorrect service procedures.

  1. Connect a battery load tester and a voltmeter across the battery terminals (the battery cables should be disconnected from the battery). Apply a 300 amp load to the battery for 15 seconds to remove the surface charge. Remove the load.
  3. Wait 15 seconds to allow the battery to recover. Apply the appropriate test load, as specified on the battery label, for 15 seconds while reading the voltage, then disconnect the load. Some appropriate loads on original batteries are:

    75-60-260 amps
    78A-72-300 amps
    83-50-150 amps
    83-60-180 amps
    85A-60-170 amps
    87A-60-230 amps
    89A-60-270 amps
    1981103-200 amps
    1981104-250 amps
    1981105-270 amps
    1981577-260 amps

  5. Check the results against the appropriate minimum voltage based on the battery temperature. If the battery voltage is at or above the specified voltage for the temperature listed, the battery is good. If the voltage falls below what's listed, the battery should be replaced.

    70°F or above-9.6 volts
    60°F-9.5 volts
    50°F-9.4 volts
    40°F-9.3 volts
    30°F-9.1 volts
    20°F-8.9 volts
    10°F-8.7 volts
    0°F -8.5 volts



See Figures 5, 6, 7, 8, 9 and 10

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Fig. Fig. 5: Maintenance is performed with household items and with special tools like this post cleaner

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Fig. Fig. 6: The underside of this special battery tool has a wire brush to clean post terminals

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Fig. Fig. 7: Place the tool over the terminals and twist to clean the post

Once a year (or as necessary), the battery terminals and the cable clamps should be cleaned. Loosen the clamps and remove the cables, negative cable first. On batteries with posts on top, the use of a puller specially made for this purpose is recommended. These are inexpensive and available in most auto parts stores. Side terminal battery cables are secured with a small bolt.

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Fig. Fig. 8: A special tool is available to pull the clamp from the post

Clean the cable clamps and the battery terminal with a wire brush, until all corrosion, grease, etc., is removed and the metal is shiny. It is especially important to clean the inside of the clamp (an old knife is useful here) thoroughly, since a small deposit of foreign material or oxidation there will prevent a sound electrical connection and inhibit either starting or charging. Special tools are available for cleaning these parts, one type for conventional top post batteries and another type for side terminal batteries.

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Fig. Fig. 9: Clean the battery terminals until the metal is shiny

Before installing the cables, loosen the battery hold-down clamp or strap, remove the battery and check the battery tray. Clear it of any debris, and check it for soundness (the battery tray can be cleaned with a baking soda and water solution). Rust should be wire brushed away, and the metal given a couple coats of anti-rust paint. Install the battery and tighten the hold-down clamp or strap securely. Do not overtighten, as this can crack the battery case.

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Fig. Fig. 10: The cable ends should be cleaned as well

After the clamps and terminals are clean, reinstall the cables, negative cable last; DO NOT hammer the clamps onto post batteries. Tighten the clamps securely, but do not distort them. Give the clamps and terminals a thin external coating of grease after installation, to retard corrosion.

Check the cables at the same time that the terminals are cleaned. If the cable insulation is cracked or broken, or if the ends are frayed, the cable should be replaced with a new cable of the same length and gauge.


The chemical reaction which takes place in all batteries generates explosive hydrogen gas. A spark can cause the battery to explode and splash acid. To avoid serious personal injury, be sure there is proper ventilation and take appropriate fire safety precautions when connecting, disconnecting, or charging a battery and when using jumper cables.

A battery should be charged at a slow rate to keep the plates inside from getting too hot. However, if some maintenance-free batteries are allowed to discharge until they are almost "dead,'' they may have to be charged at a high rate to bring them back to "life.'' Always follow the charger manufacturer's instructions on charging the battery.


See Figure 11

When battery replacement becomes necessary, select a battery with a rating equal to or greater than the one which was originally installed. Deterioration and aging of the battery cables, starter motor, and associated wires makes the battery's job harder in successive years. The slow increase in electrical resistance over time makes it prudent to install a new battery with a greater capacity then the old. Details on the role the battery plays in the vehicle's electrical systems are covered in Chapter 3 of this manual.

Always use caution when working on or near the battery. Never allow a tool to bridge the gap between the negative and positive battery terminals. Also, be careful not to allow a tool to provide a ground between the positive cable and any metal component on the vehicle. Either of these conditions will cause a short leading to sparks and possibly, personal injury.

  1. Carefully disconnect the negative battery cable from the battery terminal.
  3. With the negative battery cable disconnected and out of the way, carefully disconnect the positive cable from the battery terminal.
  5. Loosen the nut and/or bolt retaining the battery retainer strap or clamp. Remove or reposition the battery retainer.
  7. Wearing an old pair of work gloves or using a battery lifting tool to protect from any remaining battery acid, carefully lift the battery out of the vehicle and place it in a safe location. Be sure to keep the battery away from open flame and to protect surrounding areas from acid.

To install:
  1. Inspect the battery tray and cables for damage or corrosion. As necessary, clean or repair the tray and cables.

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    Fig. Fig. 11: Common battery and tray installation

  3. Carefully lower the battery into position in the tray, making sure not to allow the terminals to short on any bare metal during installation.
  5. Position and secure the battery retainer strap or clamp.
  7. Connect the positive battery cable to the battery terminal.
  9. Connect the negative battery cable to the battery terminal.