For 1990-2009 cars

### 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.

### DTC Descriptors

DTC B1390: Device Voltage Reference Input 1 Circuit - GBCM

### Circuit/System Description

The generator battery control module (GBCM) monitors the battery voltage for precision electrical power management. The generator battery control module monitors both the battery sense positive voltage circuit and the battery sense negative, ground, circuit to precisely determine system voltage. If there is a difference between the less precise battery voltage, battery positive voltage circuit and ground circuit, and the more precise battery sense voltage of 1.5 volts for 7 seconds, then DTC B1390 will set.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

The difference between the low precision battery voltage reading and the high precision battery voltage reading is greater than 1.5 volts for 7 seconds.

### Action Taken When the DTC Sets

• | The driver information center (DIC) displays the SERVICE CHARGE SYS message.

• | The GBCM uses the less accurate battery positive voltage circuit for voltage readings.

### Conditions for Clearing the DTC

• | During the current ignition cycle, the difference between the less precision battery positive voltage circuit reading and the high precision battery voltage sense circuit reading is less than 1.5 volts.

• | The SERVICE CHARGE SYS message will turn off 7 seconds after the voltage returns to normal.

### Diagnostic Aids

• | A possible cause of this DTC could be overcharging with a battery charger or jump starting.

• | A high voltage value in multiple modules indicates a concern in the charging system.

### Reference Information

#### Schematic Reference

Control Module References

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Charging System Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Engine running, accessories OFF, measure and record the battery voltage at the battery terminals. The voltage should be between 12.6 and 15.0 volts.

⇒ | If not within the specified range, refer to Charging System Test .

2. Observe the scan tool BCM Battery Voltage Signal parameter and the Batt. Voltage High Res. parameter. The readings for both parameters should be between 12.6 and 15.0 volts, and should be within 1.5 volts of each other.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connectors at the GBCM.
2. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 1 minute. Test for less than 5 ohms between the ground circuit terminals listed below and ground:

• | Terminal F

• | Terminal H

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Verify that a test lamp illuminates between the B+ circuit terminals listed below and ground:

• | Terminal A

• | Terminal C

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

4. If all circuits test normal, replace the GBCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for GBCM replacement, setup and programming.