Auxiliary Battery System Malfunction (9C1)

Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. Diagnostic Fault Information

Circuit Number	Circuit Function	Short to Ground	Open/High Resistance	Short to Voltage
4832	Relay Control	KR81 Auxiliary Battery Relay Will Not Turn On	KR81 Auxiliary Battery Relay Will Not Turn On	KR81 Auxiliary Battery Relay Will Always Be On
642	B+ Control	F5BA 100 Amp Fuse Will Open	C1B Battery - Auxiliary Will Not Charge	Batteries May Become Discharged
7650	Ground	KR81 Auxiliary Battery Relay Will Not Turn On	KR81 Auxiliary Battery Relay Will Not Turn On	—

Circuit/System Description The purpose of the KR81 Auxiliary Battery Relay, is to prevent the C1 Battery from being discharged when the vehicle is not running and accessories connected to the X50EA Battery Distribution Fuse Block - Auxiliary are used or left on. It also allows the C1B Battery - Auxiliary voltage to be maintained while the vehicle is running. The K9 Body Control Module (BCM) controls the KR81 Auxiliary Battery Relay by applying voltage to the relay coil control circuit 4892 and is grounded by ground circuit 7650. The ignition circuit 4892 is energized when the ignition is On in the Propulsion Mode. The C1 Battery voltage is supplied to the KR81 Auxiliary Battery Relay Terminal 3 circuit 642, when the Relay is energized and closes, battery voltage is supplied to the KR81 Auxiliary Battery Relay Terminal 5 which allows the C1B Battery - Auxiliary to be Charged. Reference Information Schematic Reference Starting and Charging Schematics Connector End View Reference Master Electrical Component List Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Charging System Test Circuit/System Verification

Ignition On Propulsion Mode (engine running).
All accessories OFF, slowly increase the engine speed to 2500 RPM.
Verify voltage measured at the C1B Battery — Auxiliary is within 1 V of voltage measured at the C1 Battery—Primary. ⇒ If not within 1 V 3.1. Cycle the ignition On and Off, between Off an Propulsion Modes multiple times. Verify the KR81 Auxiliary Battery Relay turns On and Off by feeling and/or listening for a click. ⇒ If the component does not turn On and Off Refer to: Circuit/System Testing Relay Does Not Cycle On and Off ⇓ If the component turns On and Off Refer to: Circuit/System Testing Relay Cycles On and Off ⇓ If within 1 V
The condition is currently not present and may be an intermittent fault. Circuit/System Testing KR81 Auxiliary Battery Relay Does Not Cycle On and Off
Ignition Off.
Verify a test lamp illuminates between the KR81 Auxiliary Battery Relay ground terminal 2 and B+. ⇒ If the test lamp does not illuminate 2.1. Test for open/high resistance in ground circuit 7650. ⇒ If open/high resistance is found, repair the circuit or ground connection. ⇓ If open/high resistance is not found 2.2. Replace the X50EA Battery Distribution Fuse Block - Auxiliary. ⇓ If the test lamp illuminates
Cycle the ignition ON, in Propulsion Mode,
Verify a test lamp turns illuminates between the KR81 Auxiliary Battery Relay control circuit terminal 1 and ground. ⇒ If the test lamp does not illuminate 4.1. Ignition OFF. 4.2. Disconnect the X2 connector at the K9 Body Control Module. 4.3. Test for a short to ground in control circuit 4892. ⇒ If a short is found, repair the circuit. ⇓ if a short to ground is not found 4.4. Test for open/high resistance in control circuit 4892. ⇒ If open/high resistance is found, repair the circuit. ⇓ If open/high resistance is not found. 4.5. Replace the K9 Body Control Module. ⇓ If the test lamp turns On
Verify a test lamp turns On and Off between the KR81 Auxiliary Battery Relay control circuit terminal 1 and ground while cycling the ignition On and Off, between Off an Propulsion Modes multiple times. ⇒ If the test lamp is always On 5.1. Turn the Ignition OFF. 5.2. Disconnect the X2 connector at the K9 Body Control Module. 5.3. Turn the Ignition ON, Run Mode. 5.4. Test for a short to voltage in control circuit 4892. ⇒ If a short to voltage is found, Repair the circuit. ⇓ If a short to voltage is not found. 5.5. Replace the K9 Body Control Module. ⇓ If the test lamp turns On and Off
Replace the KR81 Auxiliary Battery Relay. KR81 Auxiliary Battery Relay Cycles On and Off
Ignition Off.
Disconnect the X50EA Battery Distribution Fuse Block - Auxiliary from the C1B Battery - Auxiliary.
Verify a test lamp illuminates between the KR81 Auxiliary Battery Relay Terminal 3 and ground. ⇒ If the test lamp does not illuminate and the circuit fuse is open Replace the X50EA Battery Distribution Fuse Block - Auxiliary. ⇒ If the test lamp does not illuminate and the circuit fuse is good 3.1. Verify a test lamp illuminates between the X50EA Battery Distribution Fuse Block - Auxiliary Terminal 1 X1 and ground. ⇒ If the test lamp does not illuminate 3.2. Test circuit 642 for an open/high resistance. ⇒ if an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found. 3.3. Verify the X50B Battery Distribution Engine Compartment Fuse Block fuse F5BA is not open, and there is voltage at the fuse. ⇒ if the fuse is open repair the short to ground on circuit 642 ⇓ If the fuse is not open and there is no voltage at the fuse 3.4. Replace the X50B Battery Distribution Engine Compartment Fuse Block. ⇓ If the test lamp Illuminates
Ignition On, Run Power Mode.
Verify a Test lamp illuminates between the X50EA Battery Distribution Fuse Block - Auxiliary C1B Battery - Auxiliary battery clamp and ground. ⇒ If the test lamp does not illuminate 5.1. Verify a Test lamp Illuminates between the KR81 Auxiliary Battery Relay Terminal 5 and ground. ⇒ If the test lamp does not illuminate, replace the KR81 Auxiliary Battery Relay.
Replace the X50EA Battery Distribution Fuse Block.