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 Descriptor

DTC B1487: Generator L-Terminal Circuit Low

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Generator Turn On Signal | B1487 | -- | B1488 | --

### Circuit/System Description

The generator battery control module (GBCM) controls the generator through the generator turn on signal circuit, or L-Terminal circuit. The signal is a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle when the engine is running is between 5-100 percent. If the generator turn on signal circuit is in the 0-5 percent range, or pulled low to ground, then DTC B1487 will set.

### Conditions for Running the DTC

• | The engine is running.

• | This diagnostic shall run every 100 ms.

### Conditions for Setting the DTC

The generator turn on signal circuit is less than 5 percent duty cycle for 2 minutes.

### Action Taken When the DTC Sets

• | The charge indicator turns ON.

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

### Conditions for Clearing the DTC

• | The DTC will pass when the generator turn on signal circuit input is greater than 5 percent duty cycle.

• | The charge indicator and DIC message will remain ON until the ignition switch is cycled after the DTC is cleared.

### Reference Information

#### Schematic Reference

Starting and Charging Schematics

#### 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 Testing

1. Ignition OFF, disconnect the harness connector at the generator.
2. Ignition ON, GEN L-Terminal Signal Command 0%, test for less than 1 volt between the generator turn on signal circuit terminal 1 X1 and ground.

⇒ | If greater than the specified range, test the generator turn on signal circuit for a short to voltage. If the circuit tests normal, replace the GBCM.

3. Command the GEN L-Terminal Signal ON to 80% duty cycle with a scan tool. Test for 3.0 volts between the generator turn on signal circuit terminal 1 X1 and ground.

⇒ | If less than the specified value, test the generator turn on signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the GBCM.

4. If the circuit tests normal, replace the generator.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Generator Replacement

• | Control Module References for GBCM replacement, setup, and programming.