Diagnosis And Testing - Dual Batteries - 12 Volt System

DIAGNOSIS AND TESTING - BATTERY SYSTEM:  The battery, starting, and charging systems are inter-related. The diagnostics covered below are testing the complete system. In order for the engine to start and the batteries to maintain a proper charge, all of the components that are used in these systems must perform within specifications. It is important that the battery, starting, and charging systems be thoroughly tested and inspected any time a battery needs to be charged or replaced. The cause of abnormal battery discharge, overcharging or early battery failure must be diagnosed and corrected before a battery is replaced and before a vehicle is returned to service. The Powertrain Control Module (PCM) monitors these systems for faults. If the PCM has a Diagnostic Trouble Code (DTC) stored against any of these systems, the DTC(s) should be diagnosed using the DTC diagnostic test procedure.

PRELIMINARY BATTERY CHECKS:  Verify each of the following before charging and testing the batteries.

1. Inspect the batteries for any physical damage to the batteries or posts.
   • If physical damage is obvious, replace the battery and retest.
2. Verify the batteries are the proper size and rating for the vehicle. Refer to TECHNICAL SPECIFICATIONS  .
   • If the either battery does not meet the required specifications, replace the battery and retest.
3. Verify the battery and cable connections are tight and clean. Check the battery cable connections at the battery posts, alternator terminal and ground locations.
   • Clean and repair any poor connections and retest.
4. Verify the charging system is operating properly.
   • If the charging system output is low, repair the inoperative charging system.
5. If the vehicle has a no crank condition but the electrical system has power check the starting system operation.
   • Repair the inoperative starting system if required.
6. If applicable, check the battery electrolyte level. Always use the necessary safety precautions when working with batteries to prevent possible serious or fatal injury.
   • If the electrolyte level is low, fill to the proper level and retest.
7. If the battery, starting and charging systems test good, but the battery discharges after sitting for a short period, check the electrical system for an ignition off draw. Refer to IGNITION OFF DRAW TEST  .

If all preliminary checks are good, continue testing the battery system below.

CHECK FOR A BATTERY DISCONNECT:  Besides an open or poor cable connection, the two components that can cause a disconnect between the batteries is the power control relay and the fuse.

TECH TIPS:

• The normally closed power control relay should be closed 99% of the time. It is only opened by the PCM during the starter in-rush at initial engine cranking.
• On vehicles with a fuse array, the nuts that connect the cables to the fuse array can loosen and lose the proper torque. This can cause an excessive current draw condition damaging the fuse and causing a disconnect between the power control relay and main battery. This can often be seen by discoloration of the cable ends at the fuse location.

CHECKING FOR A DISCONNECT BETWEEN THE BATTERIES: 

1. This step is checking for a disconnect between the batteries at the power control relay.  Measure the voltage at the C3-1 and C8-1 cable end terminals at the Power Distribution Center (PDC). This can be done with the engine running, with the ignition on or off. The voltage should be the same at both terminals except during the starter in-rush at initial engine cranking.
   1. If the voltage is not  the same at both terminals, there is a disconnect between the batteries at the power control relay or the fuse in the fuse array.  The power control relay can be stuck open if it is being energized. This can happen if there is voltage on the control circuit due to the PCR control relay in the PDC being stuck on or the control circuit is shorted to voltage. Continue to step 2.
   2. If the voltage is the same at both terminals, the fuse is not open ant the relay is not stuck open. Continue to step 4.
2. Disconnect the PDC connector for the power control relay. This should cause the relay to de-energize and close if it is being electrically held on (open). Measure the voltage at the C3-1 and C8-1 cable end terminals again.
   1. If the voltage is still not the same, the power control relay is faulty. Replace the PDC in accordance with the service information.
   2. If the voltage is now equal, check the (T760) circuit for a short to voltage. If the circuit is not shorted to voltage, replace the PDC in accordance with the service information.
   3. If the (T760) circuit is shorted to voltage, repair the circuit and retest.
3. Check fuse F11 (150A) in the fuse array for an open.
   1. If the fuse is open, replace the fuse array in accordance with the service information. Be sure to torque the nuts correctly for the cables connecting to the fuse array. Failure to torque the nut properly can cause an excessive current draw and damage the new fuse array fuses. 
   2. If the fuse is not open, replace the PDC in accordance with the service information.
4. Disconnect the C3-1 and C8-1 cable end terminals from the PDC. Be sure not to allow the cables to contact ground as they are still connected to the batteries.  Measure the voltage at each terminal end to determine which side of the system requires testing. If there is an issue with one of the batteries being depleted it will measure low voltage on that side of the system. A poor connection may not show up by measuring voltage. If they both appear OK, it may be necessary to load test each cable to determine if there is resistance in the cables between each battery and cable end at the PDC.
   1. Check the cables and cable connections for the side of the system that had low voltage or failed a load test.
      • Main battery side - Check the connections at the pass through, main battery cable ends and cables in between.
      • Auxiliary battery side - Check the connections at the pass through, auxiliary battery cable ends, rear power distribution center, and cables in between.
   2. If the cables and connections are good, continue to the CHECKING FOR A DEPLETING OR DEPLETED BATTERY below to test the suspect battery.
   3. If the cables or connections have a poor connection, repair the poor connection and retest the system.

CHECKING FOR A DEPLETING OR DEPLETED BATTERY: Previous service information reported never to blind charge the battery around the Intelligent Battery Sensor (IBS). Software changes to the GR8 battery tester have improved how the battery is tested. However, this requires the GR8 battery tester to be connected directly to the battery posts, bypassing the IBS. 

1. Disconnect the battery positive and negative cables to isolate the battery. If both batteries are not disconnected, the positive cable will still have voltage through it's connection to the other battery. Isolate the positive cable end so that it cannot touch ground or disconnect both batteries to be certain the 12 volt system is powered down. Connect the (special tool #GR8-1220KIT-CHRY, AGM Battery Tester/Charger Station) directly to the battery posts and select the battery charging and testing procedure on the screen.
2. Follow the prompts on the GR8 battery tester screen and fill in the vehicle information.
3. When the battery test has completed, the tester will display the results on the screen.
4. While viewing the battery test result, press the CODE button and the tester will prompt you for the last 4 digits of the Vehicle Identification Number (VIN). Use the UP/DOWN arrow buttons to scroll to the correct character; then press ENTER to select and move to the next digit. Then press the ENTER button to view the SERVICE CODE. Pressing the CODE button a second time will return you to the test results.
   1. If the battery fails the load testing below, record the failure code and replace the battery.
   2. If the battery DOES NOT fail the load testing below, reconnect the battery and retest the system. If the battery, starting and charging systems test good, but the battery discharges after sitting, check the electrical system for an ignition off draw. Refer to IGNITION OFF DRAW TEST  .