Hummer H3. Manual - part 32

Typical Scan Tool Data

GEN F-Terminal Signal - ECM

Circuit/System Description

The generator battery control module (GBCM) and the engine control module (ECM) monitor
the generator through the generator field duty cycle signal circuit. The signal is a pulse width
modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is
between 5-99 percent. If the generator field duty cycle signal circuit is in the 0-5 percent range or
pulled low to ground while the engine is running, then the GBCM will set DTC B1492.

Conditions for Running the DTC

The engine is running.

The engine speed is less than 1,000 RPM.

DTC B1487 or B1488 is not set as a current DTC.

Conditions for Setting the DTC

The generator field duty cycle signal circuit is less than or equal to 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 CHARGSYS message.

Conditions for Clearing the DTC

The generator field duty cycle signal circuit input is greater than 5 percent duty cycle.

The charge indicator and the SERVICE CHARGSYS message will remain ON until the
next ignition cycle.

Generator Field Duty Cycle
Signal

B1492

Circuit

Short to

Ground

Open

Short to Voltage

Operating Conditions: Engine Running
Parameter Normal Range: 5% to 99%
Generator Field Duty Cycle Signal

99%

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

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 Verification

1. Engine running, observe the scan tool ECM GEN-F Terminal Signal parameter. The

parameter should read between 5 and 99 percent.

If not within the specified range, refer to Circuit/System Testing.

2. Verify that the GBCM does not set DTC B1492.

If the GBCM sets DTC B1492, refer to Circuit/System Testing.

Circuit/System Testing

ECM Generator Field Duty Cycle Signal Circuit Malfunction

1. Ignition OFF, disconnect the harness connectors at the generator and GBCM.

2. Ignition ON, engine OFF, connect a test lamp to B+ and repeatedly probe the generator

field duty cycle circuit terminal 2 of the generator while monitoring the ECM GEN-F

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

Terminal Signal parameter. The parameter should change from less than 5 percent to greater
than 95 percent.

If the parameter was not affected by the test lamp, test the circuit for a short to voltage,
short to ground, or an open/high resistance. If the circuit tests normal, replace the
ECM.

3. Reconnect the harness connector at the GBCM.

4. Repeatedly probe the generator field duty cycle circuit terminal 2 of the generator with the

test lamp that is connected to B+, harness side while monitoring the ECM GEN-F Terminal
Signal parameter. It should change from less than 5 percent to greater than 95 percent.

If the parameter was not affected by the test lamp, replace the GBCM.

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

GBCM Generator Field Duty Cycle Signal Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the GBCM.

2. Ignition ON, engine OFF, connect a test lamp to B+ and repeatedly probe the generator

field duty cycle circuit terminal B of the GBCM while monitoring the ECM GEN-F
Terminal Signal parameter. The parameter should change from less than 5 percent to greater
than 95 percent.

If the parameter was not affected by the test lamp, test the circuit for a short to voltage,
short to ground, or an open/high resistance.

3. If the circuit tests normal, replace the GBCM.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Generator Replacement (LH8) or Generator Replacement (LLR)

Control Module References for ECM or GBCM replacement, setup, and programming

DTC B1516

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

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

DTC B1516

Battery Current Sensor Performance - GBCM

Circuit/System Description

The generator battery control module (GBCM) monitors its internal battery current sensor for
many charging system operations, and also for diagnostic purposes. When the values of the
internal battery current sensor go out of range, DTC B1516 will set.

Conditions for Running the DTC

The engine is running.

This diagnostic shall be run every 50 ms.

Conditions for Setting the DTC

The duty cycle of the internal battery current sensor is less than 2 percent duty cycle or greater
than 98 percent duty cycle for 4 minutes.

Action Taken When the DTC Sets

The charge indicator turns ON.

The driver information center (DIC) displays the SERVICE CHARGSYS message.

The generator field control circuit duty cycle is set to 100 percent.

The filtered battery current is set to 0.1 amp.

The battery voltage parameter defaults to 13.8 volts.

Conditions for Clearing the DTC

The duty cycle of the internal battery current sensor is greater than 2 percent duty cycle or less
than 98 percent duty cycle.

Reference Information

Schematic Reference

Starting and Charging Schematics

Connector End View Reference

Component Connector End Views

2008 Hummer H3

2008 ENGINE Engine Electrical - H3

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