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 battery 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 BATTERY 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.

CHECKING FOR A DISCONNECT BETWEEN THE BATTERIES:  Besides an open cable or poor 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 de-energized and closed 99% of the time. It is only opened by the PCM during the starter in-rush at initial engine cranking.
• On some 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.

1. This step is checking for a disconnect between the batteries at the power control relay.  Measure the voltage at both cable end terminals of the power control relay. This can be done with the engine running, with the ignition on or off. The voltage should be the same at both terminals.
   1. If the voltage is not the same on both terminals, the normally closed relay is stuck open. The power control relay will 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 if the control circuit is shorted to voltage. Continue to step 2.
   2. If the voltage is the same at both terminals, the relay is not stuck open. Continue to step 3.
2. Disconnect the power control relay harness connector. This should cause the relay to de-energize and close if it is being electrically held on (open). Check for voltage on the control circuit.
   1. If voltage is present, the PCR control relay inside the PDC is stuck on, or the control circuit between the PCR control relay and the power control relay is shorted to voltage.
   2. If voltage is NOT present, and the relay is still open with the harness connector unplugged, replace the faulty power control relay.
3. Measure the voltage across the terminals of the main battery. Compare the main battery voltage to the voltage at the power control relay terminals. If there are no disconnects between the main battery and power control relay, the voltage readings will be the same.
   1. If the voltage reading at the power control relay is lower than the main battery voltage, there is a disconnect. Check the fuse in the system between the main battery and power control relay. If the fuse is open, verify the cables are not shorted to ground and replace the fuse or fuse array depending on vehicle configuration. If the fuse to good, check the positive cables and connections on the main battery side of the system for opens or poor connections.
      NOTE:

      It is very important to torque the nut holding the cables to the correct specification. A loose torque on a cable nut can cause excessive current draw on the system and damage the fuse.

   2. If the main battery voltage matches the power control relay, continue to the CHECKING FOR A DEPLETING OR DEPLETED AUXILIARY BATTERY service information below.

CHECKING FOR A DEPLETING OR DEPLETED AUXILIARY BATTERY:  On some vehicles the auxiliary battery can be difficult to access for testing with the GR8 battery tester. This service information describes an alternative way of to perform a State Of Charge (SOC) check of the auxiliary battery to determine if the GR8 battery tester should be used. This should be done after testing for and determining there is not a disconnect between the main battery and power control relay.

TECH TIPS:

• If the auxiliary battery requires testing with the GR8 battery tester, the GR8 battery tester must be connected directly to the battery posts. 
• After either battery is charged or replaced, an IBS reset should be performed. If the IBS reset is not performed, it can take several days of run time and sleep cycles for the IBS to learn the battery SOC after a battery is blind charge or replaced. The IBS reset allows the IBS to start with a default 80% SOC, and will detect that the battery has been charged or replaced. This can allow many of the vehicle features to operate normally. The IBS also initiates a quick learning curve which allows the IBS to update the actual battery SOC after a 4 hour sleep cycle.

1. Turn the ignition off. To check the auxiliary battery SOC, measure the voltage as close to the auxiliary battery as possible (recommend at the power control relay). Disconnect the main battery positive cable. Use caution  when disconnecting the positive cable since the electrical system is still connected to and powered by the auxiliary battery. The auxiliary battery voltage should not drop off drastically. Typically it should still be above 12v if the battery is charged properly.
   1. If the voltage drops sharply when the main battery is disconnected, verify a good auxiliary battery ground cable connection at the main battery negative terminal. If the connection is good, the auxiliary battery should be isolated and tested with the GR8 battery tester. Refer to the CHECKING FOR A DEPLETING OR DEPLETED BATTERY WITH THE GR8 TESTER service information below.
      • Perform an IBS reset by removing the IBS from the battery cable end and disconnecting the IBS harness connector for 30 seconds after an auxiliary battery is charged or replaced. This will allow the IBS to default to an 80% SOC and initiate the quick learning curve.
   2. If the voltage is near or above 12v, continue to step 2.
2. To load test the auxiliary battery without the GR8 battery tester, turn the ignition on, and turn on several loads (headlights, HVAC blower, rear defrost, etc.) for approximately 1 1/2 minutes while monitoring the auxiliary battery voltage at the power control relay. DO NOT EXCEED 2 MINUTES. The voltage should be near or above 10v after approximately 1 1/2 minutes. Next turn the loads and ignition off. Monitor the voltage for another 1 1/2 minutes at the power control relay. The voltage should recover back to 12v.
   1. If the auxiliary battery does not appear to be charged or functioning as described, isolate and test the auxiliary battery at the battery posts with the GR8 battery tester.
      • Perform an IBS reset by removing the IBS from the battery cable end and disconnecting the IBS harness connector for 30 seconds after an auxiliary battery is charged or replaced. This will allow the IBS to default to an 80% SOC and initiate the quick learning curve.
   2. If the auxiliary battery appears to be charged and functioning properly, isolate and test the main battery with the GR8 battery tester. Refer to the TESTING A BATTERY WITH THE GR8 TESTER service information below.

TESTING A BATTERY WITH THE GR8 TESTER:  Always use the Midtronics GR8 Instruction Manual that was supplied with the tester as a reference. If the Instruction Manual is not available the following procedure can be used:

1. Disconnect the battery positive and negative cables to isolate the battery. 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  .

CHECKING FOR THE POWER CONTROL RELAY NOT DISCONNECTING PROPERLY WHEN COMMANDED DURING CRANKING:  It can be difficult to test the power control relay for properly disconnecting during an engine cranking event without using a lab scope. This is due to the relay only being energized (opened) for approximately 20-40ms.

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.
• A severely depleted auxiliary battery could set a fault due to the voltage difference between the batteries being less than the calibrated threshold during a cranking event when the batteries are separated.

1. Disconnect the power control relay harness connector. Load test the power control relay coil ground circuit.
   1. If the ground circuit fails the load test, repair the ground circuit for an open or high resistance.
   2. If the ground circuit passes the load test, reconnect the power control relay harness connector.
      • Continue to step 2 to test without a lab scope.
      • Continue to step 4 to test with a lab scope.
2. The relay should energize and open when 12v is supplied to the relay on the control circuit, which comes from the output of the PCR control relay inside the PDC. The PCR control relay is typically a Printed Circuit Board (PCB) relay which cannot be removed and jumped across. Turn the ignition on and perform one of the following to energize the power control relay:
   1. If there is an actuator available in the scan tool, command the power control relay on.
   2. Using a test light connected to ground, back probe the PCR control relay low side driver control circuit at the PDC connector to energize the relay.
   3. Using a fused jumper connected to B+, back probe the power control relay control circuit at the power control relay harness connector to energize the relay.

   Continue to step 3.

3. With 12v provided to the power control relay, measure the voltage at both cable end terminals of the power control relay. If the relay is disconnected, the voltage on the auxiliary battery terminal should start to drop below the voltage on the main battery terminal due to the load on the auxiliary battery.
   1. If the voltage starts to drop on the terminal that leads to the auxiliary battery, the relay is functioning properly.
   2. If the voltage drops drastically below approximately 8v on the terminal connected to the auxiliary battery, isolate and test the auxiliary battery with the GR8 battery tester.
   3. If the voltage at both terminals remains the same, replace the power control relay and retest.
      • Perform an IBS reset by removing the IBS from the battery cable end and disconnecting the IBS harness connector for 30 seconds after an auxiliary battery is charged or replaced. This will allow the IBS to default to an 80% SOC and initiate the quick learning curve.

   Courtesy of CHRYSLER GROUP, LLC

4. To test with a lab scope, connect channel A to the main battery side terminal of the power control relay. Connect channel B to the auxiliary battery side terminal of the power control relay. Connect channel C to the control circuit at the power control relay. Set the channels to the 20v scale. Crank the engine and record the voltage reads. The voltage on the main battery (channel A) side should drop considerably during cranking. At initial starter in-rush the voltage can drop to as low as 7.0 volts. If the power control relay is operating correctly, you should simultaneously see 12v present on the control circuit (channel C) and the auxiliary battery side voltage (channel B) should stay near 12v during the initial 20-40ms of starter engagement. After this brief period, channel C should drop back to 0v and the relay will de-energize (close), and the voltages should equalize on channel A and channel B.
   1. If the auxiliary battery voltage (channel B) stays near 12v as the main battery voltage (channel A) drops at initial cranking, the power control relay and system are functioning properly.
   2. If the auxiliary battery voltage (channel B) stays the same as the main battery voltage (channel A) when the voltage drops at initial cranking, the power control relay likely did not open.
      • If 12v was present on the control circuit (channel C), the relay is faulty. Replace the relay and retest.
      • If 12v was NOT present on the control circuit (channel C), check the control circuit and fuse for an open. If the fuse is open, check the circuit for a short to ground. If the circuit and fuse check good, check the operation of the PCR Control Relay inside the PDC.
   3. If the auxiliary battery voltage (channel B) drops severely (below approximately 8.0 volts) but is not the same as the main battery voltage (channel A) at initial cranking, the auxiliary battery is likely faulty or severely undercharged. Test the auxiliary battery using the GR8 Battery Tester.