III. Battery Diagnosis - Vehicle Related Condition

After the battery has been charged or tested and has proven to be a good battery, the cause of the no-start or slow cranking condition must be determined and corrected to avoid comebacks. If no obvious cause is evident, the vehicle's electrical system should be diagnosed using the following steps:


Step 1 - Check Cranking System

If the battery has tested OK on a load test and the vehicle still will not start or is difficult to start, the cranking system should be checked; otherwise, proceed to Step 2.
Check the visual condition of the battery, battery cables and connections, and check for the presence of the green dot on the built-in hydrometer. If the built-in hydrometer is dark ("black eye", green dot not present), charge and test the battery as described previously in Section II before continuing the cranking system diagnosis. To check the cranking system to verify proper operation, a simple cranking test can be done as follows:

a. Prevent the car from starting during cranking by one of the following methods:

i. V6 and V8 gasoline - remove the battery lead (BAT Terminal) from the distributor. ii. Diesel - remove the pink wire at the injection
pump.
iii. 1982 Cavalier - remove and ground the secondary
coil wire at the distributor (center wire on distributor cap).

CAUTION: Coil wire must be grounded to prevent a high voltage spark which could cause a shock or fire hazard and possibly result in personal injury or property damage. iv. 1983 Cavalier, Citation and Camaro Z28 - remove
fuel pump fuse.

v. Connect a voltmeter from the positive terminal of the starter to ground.

c. Turn key to start position and read voltmeter while cranking, using care not to run the starter motor continuously for over 30 seconds. If starter is run for 30 seconds, it must be allowed to cool for at least 3 minutes before cranking to avoid possible damage.

d. If the voltage noted in Step C above is less than 9.6 volts at 21~C- (70~F) during cranking and the battery has already checked OK (greater than 9.6 volts on load test), an excessive current draw from the starter or an excessive voltage drop in the starter cables could be the cause of low cranking voltage; proceed to Step E below. If the voltage measured while cranking is greater than 9.6 volts (i.e., the starting system checks OK), proceed to Step F below.
e. Diagnose the starting system as described in the Chevrolet Service Manual, noting in particular the voltage drops in the system which would indicate either excessive resistance or poor or corroded connections. The threaded end of the battery cable screw and the lead contact faces on the battery terminals and cables should be cleaned with a wire brush if necessary, and the cables should be properly torqued to 12 N-m. (105 in.lbs.).

f. Reconnect the leads disconnected in Step 1a, Page 12.

g. If the starting system checks above reveal no abnormal conditions, but excessive cranking is required to start the car, the cause should be diagnosed and corrected to reduce battery demands. Two possible causes for excessively long cranks are the engine fuel system or the HEI distributor system. Refer to the engine diagnosis sections of the Chevrolet Shop Manual for further information concerning these causes.


Step 2 - Check For Current Drain

If a battery requires recharging and no cause is evident (i.e., headlamps left on, extended vehicle storage, etc.), the vehicle should be diagnosed for excessive current drain. Excessive current drain occurring while a car is parked (ignition switch off) can cause a discharged battery, which could be improperly diagnosed as one which will not hold a charge. Current drain can be accurately checked using digital multimeter J-29125 and two alligator clip-type jumper wires as follows:

a. Disconnect the negative battery cable (both negative cables on diesel vehicles).

b. Install a battery side terminal adapter (AC Delco ST-1201 or equivalent) in the negative terminal of the battery.

NOTE: Except as noted in Section II, Step C (page 3), a bolt should not be used for this test or any other battery testing or charging operations, as a good contact with the lead face of the terminal is essential for proper testing and charging. If side terminal adapters are not available, see Section II for the proper way to use a bolt and nut to assure good electrical contact.

c. Install a 3/8-16 nut with standard threads (16 UNC) on the negative battery cable terminal attaching screw to assure a good electrical contact with the lead face on the cable for testing.

d. Set multimeter J-29125 to DC, MA (milliamps), and the 2,000 range.

Figure 6 - Battery Drain Test Circuit:

e. With all lights, accessories and the ignition switch off, connect the multimeter in series with the battery as shown in Figure 6, below. (Note that for a diesel, one battery remains disconnected from the circuit for this test.)
Possible causes of excessive current draw are such conditions as a misadjusted trunk lamp switch, a glove box lamp which stays on due to a misadjusted door, a pinched or grounded wire, etc. A very small current draw (under 50 milliamps) is normal for the clock, the memory electronics in the radio, the voltage regulator, ECC and ECM.
Step 3 - Check Charging System

If a battery becomes discharged and no excessive current drain is found in Step 2 above, the operation of the charging system should be checked as follows:

a. Check for proper operation of the generator tell-tale instrument panel lamp. Replace the bulb or fuse or repair the wiring as necessary.

b. Check belt tension, using belt tension gage J-23600, against the specifications given in the Chevrolet Shop Manual. Be sure to check the A.I.R. pump drive belt on 1980 through 1983 models with V8 gasoline engines, as this belt drives the water pump, which in turn drives the generator.

c. Check the charging system and battery wiring, including the connectors at the generator and bulkhead and battery terminals for cleanliness and tightness.

d. Use generator tester J-26290 to differentiate between failures in the generator or the wiring harness as necessary. The use of tester J-26290 is described in the Chevrolet Shop Manual.

e. If in doubt concerning the output of the generator, check generator output as described in the Chevrolet Shop Manual. If generator output is within 10 amperes of rated output, the generator is not the cause and should not be replaced.