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 C0300: Rear Speed Sensor Malfunction

Circuit/System Description

The rear propshaft speed sensor is a permanent magnet generator. The permanent magnet generator produces a pulsing AC voltage. The AC voltage level and number of pulses increase as speed increases. The module converts the pulsating AC voltage to a propshaft RPM which is used for calculations. The propshaft RPM can be displayed with a scan tool.

This DTC detects an open, short to ground, short to voltage, or faulty sensor.

Conditions for Running the DTC

    • The ignition is ON.
    • System voltage is 9-18 volts.
    • Vehicle speed exceeds 16 km/h (10 mph).

Conditions for Setting the DTC

The system logs the DTC if the rear propshaft input indicates a speed of less than 16 RPM for 30 seconds while all of the following are true:

    • The transmission is NOT in PARK/NEUTRAL.
    • The engine is running.
    • Vehicle Speed On Class 2 Data bus exceeds 16 km/h (10 mph).

Action Taken When the DTC Sets

    • All shifts to AUTO, Adapt mode are disabled. If the current mode is AUTO, the system does not allow any further adaptive events, correct slip.
    • The SERVICE AWD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC

    • The transfer case shift control module clears the DTC if the condition for setting the DTC no longer exists.
    • 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.