DTC C0305. GMC Truck Envoy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2008 🢒 Envoy - 2WD 🢒 DTC 🢒 DTC C0305

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 C0305: Front Speed Sensor Malfunction

The front 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 transfer case shift control module converts the pulsating AC voltage to a propshaft RPM, which is used for the following functions:

•	Calculations

•	To monitor the difference between the front and rear propshaft speed

•	In the AUTO or the Adapt mode of operation, to determine the amount of slip and the percent of torque to apply to the front axle

The module accesses this input when the vehicle is in AUTO mode, 4HI and 4LO ranges. 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 front 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.

•	The front axle is engaged.

•	The rear propshaft speed exceeds 512 RPM.

•	Vehicle speed on Class 2 Data bus exceeds 16 km/h (10 mph).

Action Taken When the DTC Sets

•	All shifts to AUTO mode are disabled. If the current mode is AUTO, the system does not allow any further adaptive events, such as correcting the slip.

•	The SERVICE 4WD 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 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

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.