Diagnostic Test

CHECKING FOR THE DBSM NOT DISCONNECTING PROPERLY WHEN COMMANDED (P2AF6): 

It can be difficult to test the DBSM 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 DBSM 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 this 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. The DBSM is located in the PDC. Disconnect the DBSM  connector. Disconnect the DBSM harness connector. Load test the DBSM 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 DBSM connector for the next step. 
      • Continue to step 2 to test without a lab scope  .
      • Continue to step 3 to test with a lab scope  .
2. Verify that the ignition is on to provide a load on the auxiliary battery. With ground provided to the DBSM control, measure the voltage at the C3-1 and C8-1 cable end terminals at the PDC. If the DBSM 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 DBSM is functioning properly. Check each of the following:
      • Check the fuses between the positive battery cable connections at the PDC and batteries.
      • Check both battery ground cables for poor ground connections.
      • Check both battery positive cable connections at the PDC and batteries for poor connections.
   2. If the voltage drops drastically below approximately 8V on the terminal connected to the main battery, isolate and test the main battery with the approved battery tester.
   3. If the voltage at both terminals remains the same, replace the DBSM in accordance with the service information 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.
3. To test with a lab scope:
   • Connect channel A to the C8-1 terminal of the PDC (Auxiliary battery connection)
   • Connect channel B to the C3-1 terminal of the PDC (Main battery connection)

   Set the channels to the 20V scale. Crank the engine and record the voltage reads. The voltage on the main battery (channel B) side should drop considerably during cranking. At initial starter in-rush the voltage can drop as low as 7.0V. If the DBSM is operating correctly the auxiliary battery side voltage (channel A) should stay near 12V during the initial 20-40ms of starter engagement. After this brief period, the DBSM will de-energize (close) causing the voltages to equalize on channel A and channel B.

   1. If the auxiliary battery voltage (channel A) stays near 12V as the main battery voltage (channel B) drops at initial cranking, the DBSM is functioning properly. Check each of the following:
      • Check the fuses between the positive battery cable connections at the PDC and batteries.
      • Check both battery ground cables for poor ground connections.
      • Check both battery positive cable connections at the PDC and batteries for poor connections.
   2. If the auxiliary battery voltage (channel A) stays the same as the main battery voltage (channel B) when the voltage drops at initial cranking, the DBSM likely did not open. Isolate and check the DBSM LSD control circuit for a low signal during a cranking event. A DVOM connected between battery voltage and the control circuit may be able to detect this during initial cranking.
      • If the DBSM LSD control circuit is pulled low at initial cranking, the relay is faulty. Replace the DBSM in accordance with the service information and retest.
      • If the DBSM LSD control circuit is not  pulled low at initial cranking, the DBSM is not the issue. Check the control circuit for the DBSM for an open. This should typically be accompanied with another DTC.
   3. If the auxiliary battery voltage (channel A) drops severely (below approximately 8.0V) but is not the same as the main battery voltage (channel B) at initial cranking, the auxiliary battery is likely faulty or severely undercharged. Continue to the CHECKING FOR A DEPLETING OR DEPLETED BATTERY information below to test the auxiliary battery using the approved Battery Tester.

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 approved Mopar® battery tester has improved how the battery is tested. However, this requires the approved Mopar® 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 approved battery tester directly to the battery posts and select the battery charging and testing procedure on the screen.
2. Follow the prompts on the approved Mopar® 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 .