Essential Tool J 42000 Battery Tester

Every General Motors dealer received a J 42000 battery tester during the 1998 model year. This battery tester is part of the essential tool package and is proven to speed up diagnosis time and reduce the errors associated with load testing technology. This bulletin is being sent to all dealers to help answer the most frequently asked questions and concerns about this new battery testing technology.

1. QUESTION: Why does J 42000 pass a battery before a load test, then fail the same battery after the load test?

ANSWER: Even though it does not happen often, an intermittent internal battery weld failure can cause a battery to give different test results, just as an intermittent connection in any circuit can be difficult to diagnose. A partial connection can cause the J 42000 to show that the battery appears to have adequate capacity. Under the high current of a load test, the weld may completely open or become resistive. The J 42000 can then recognize the problem. It is important to realize that this can also happen the other way around. A failed load test can temporarily "heal" a broken weld enough to make the J 42000 give a good test result. Intermittents are difficult to deal with in any electrical device.

2. QUESTION: Why does J 42000 fail a battery that passes a load test?

ANSWER: Good connections are very important to obtain consistent results with this tester. The J 42000 tester can be used at the battery cable while it is in the vehicle. If the J 42000 fails a battery test at the cables, you must re-test at the battery terminals with the lead lug adapters supplied or with the battery charging and testing adapters from GM (P/N 12303040). These adapters are designed to contact the lead face of the battery terminal, where the cable would normally contact. Battery bolts, common bolts, or bolt/nut/washer combinations cannot be used as substitutes for the proper test adapters. Bolts do not provide the adequate contact on the lead pad of the terminal and will not give accurate results. Bolt/nut/washer combinations can introduce several hidden resistances into the circuit. Tests using these substitutes often result in a good battery testing as bad. If the battery tester fails the battery with the proper adapters installed on clean terminals, replace the battery.

3. QUESTION: I do not get agreement in test results between the J 42000 and a load test. Why?

ANSWER: Both load testing and J 42000 testing require using the correct specifications. Be sure that the correct LOAD TEST specification is being used for load testing, while the correct CCA rating of the battery is being entered for testing with the J 42000. When proper connections are made and correct specifications are used, there is good agreement between the two testing methods. Load test equipment should be calibrated periodically to assure proper readings, while the electronic circuitry of the J 42000 does not need such maintenance.

4. QUESTION: The J 42000 passes battery with the result " Good Recharge", but later the car comes back (after charging) and the battery will not start the car. Why?

ANSWER: If the battery passes a second test with the result "Good Recharge", check the car carefully for a condition which may cause the battery to become discharged. Malfunctioning charging systems, parasitic drains and vehicle driving habits can all be causes of a discharged battery. These conditions may be especially difficult to identify if they are intermittent. A complete test of the charging system should be performed, as well as testing for parasitic drains on the car using the J 38758 Parasitic Draw Test Switch and J 39200 (Fluke 87) DMM. If excessive parasitic drains are present, find and repair the source of the drain. If the cause of the discharged battery is determined to be driving habits, education of the operator as to why the condition occurs, is the best course of action. A DISCHARGED BATTERY IS USUALLY THE RESULT OF A PROBLEM AND NOT THE CAUSE.

5. QUESTION: After charging a battery all day, the eye will not turn green, but it passes the J 42000 test and load test. Why?

ANSWER: The "eye" is a one-ball hydrometer used to gauge the specific gravity of the electrolyte (acid) in one cell of the battery. We can usually use this device to determine battery state of charge, since it relates directly to the overall specific gravity of the battery. During the charging process, the specific gravity of the electrolyte right next to the battery plates is changing rapidly. However, the electrolyte farther from the plates may become stratified or layered (not evenly mixed). This is particularly true in a battery that has been in a discharged state for a while. This stratification condition will delay the change of the eye from dark to green. When charging is complete, the eye will turn green once the electrolyte has had a chance to mix completely in that one cell. In these cases, the J 42000 allows a quicker diagnosis of the battery and returning the battery to use will cause the electrolyte to mix faster and the green ball to appear sooner.

6. QUESTION: The J 42000 gives me two different codes on two consecutive tests. Why?

ANSWER: The J 42000 is a sensitive device that carefully measures conductance and open circuit voltage. Small changes in open circuit voltage and conductance can change the test code, but typically will not change the overall test result.

7. QUESTION: Why does the J 42000 pass batteries that have a clear or yellow eye?

ANSWER: The "eye" in the battery turns clear or yellow when the electrolyte level drops below the end of the built-in hydrometer or a gas bubble becomes trapped in the hydrometer. To eliminate the possiblity of a gas bubble causing the clear eye, tap on the face of the hydrometer lightly to dislodge any bubbles. If the eye remains clear, the battery is low on electrolyte and should be replaced. An infrequent situation could occur where the electrolyte level has dropped below the end of the hydrometer, but is still covering enough of the plates so the battery has enough capacity to pass the J 42000 test. If this condition exists, the battery should still be replaced, as the low electrolyte condition will soon affect the battery performance. Conditions such as overcharging, leaks in the case and tipping the battery beyond 45° degrees for extended periods of time, are all causes for low electrolyte and clear eye hydrometer readings. These conditions should be corrected before installing a replacement battery.

8. QUESTION: Why do I get different results when I test batteries at the remote terminals and the battery terminals?

ANSWER: The resistance inside the battery cables (although very low) is enough to change the test result. Always perform your first test at the battery, with the cables attached (if possible). If access is restricted, testing at remote terminals is possible, but less accurate. If the battery fails the first test, ALWAYS remove the battery and test again using the proper adapters before condemning the battery.

9. QUESTION: I cannot find my lead lug adapters. Can I use a couple of 3/8 bolts or battery bolts?

ANSWER: Battery bolts, common bolts, or a combination of bolts, nuts and washers cannot be used as a substitute for the proper testing adapters. Bolts only contact the nut inside the terminal and the bolt/nut/washer combinations can have hidden resistances that will not give accurate results. If the lead lug adapters are not available, GM charge and test adapters (P/N 12303040) can be used as well. If the battery tester fails the battery with the lead lug adapters or P/N 12303040 installed on clean terminals, then replace the battery.

10. QUESTION: What do I do with the code and what does the code mean?

ANSWER: After you have performed the test, record the test code on the shop copy of the repair order. When you submit the warranty claim, enter the test code in the comments field of the claims screen. The test code contains the input CCA, results of the test, and any special conditions detected by the tester.

Parts are currently available from GMSPO.