GM Service Manual Online
For 1990-2009 cars only

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 B0775: Four Wheel Drive High Range (4HI) Indicator Circuit Malfunction

Circuit/System Description

The 4HI indicator circuit consists of an LED dimming supply circuit and a 4HI indicator control circuit. When the 4HI mode is selected, current is supplied to the 4HI indicator by the LED dimming supply circuit, traveling through the 4HI indicator LEDs, at which time the transfer case shift control module supplies the ground through the 4HI indicator control circuit.

Conditions for Running the DTC

    • The ignition is ON.
    • System voltage is 9-18 volts.

Conditions for Setting the DTC

    • The system monitors the voltage on the 4HI indicator control circuit.
    • If the system detects a voltage of 3 volts or less for 1.5 seconds when the 4HI indicator is not commanded, the DTC is logged.
    • If the system detects a voltage of 4.5 volts or greater when the 4HI indicator is commanded, the DTC is logged.

Action Taken When the DTC Sets

The SERVICE 4WD indicator is not illuminated.

Conditions for Clearing the DTC

    • The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
    • A history DTC clears after 100 consecutive ignition cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Reference Information

Schematic Reference

Transfer Case Control Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Transfer Case 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.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.