Chevrolet Silverado / GMC Sierra. Service manual — part 2914

Circuit/System Description

The neutral indicator circuit consists of an ignition 1 voltage circuit and a neutral indicator
control circuit. When the neutral mode has been selected, current is supplied to the neutral
indicator by the ignition 1 voltage circuit, traveling through the neutral indicator LED, at which
time the transfer case shift control module supplies the ground through the neutral indicator
control circuit.

Conditions for Running the DTC

The ignition is ON.

System voltage is 10-18 volts.

Conditions for Setting the DTC

The system monitors the voltage on the neutral indicator control circuit.

If the system detects a voltage of 2 volts or less for 1.5 seconds when the 2 high indicator is
not commanded, the DTC is logged.

If the system detects a voltage of 4.5 volts or more when the 2 high indicator is commanded,
the DTC is logged.

Action Taken When the DTC Sets

The SERVICE 4WD indicator is commanded on for this DTC for the remainder of the 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 40 consecutive warm up 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

06

06

01

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Component Connector End Views

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Scan Tool Data Definitions

Diagnostic Aids

A short to ground on the neutral indicator control circuit will cause the neutral indicator to
remain on at all times. An open or high resistance will cause the neutral indicator to be
inoperative during the 2 second bulb check.

Circuit/System Testing

Check the ignition 12 voltage reference circuit pin 2 at the transfer case shift control switch for
voltage with the ignition on.

If less than battery voltage check the 12 volt reference circuit pin 14 at the BCM and pin 2
on the transfer case mode switch for an open or high resistance. If the voltage is low or non
existent and the circuit tests good replace the BCM. If the BCM test good go to the next
step.

If the neutral indicator is on at all times check the neutral indicator control circuit for a
short to ground. If the neutral indicator is inoperative during bulb check, check the neutral
indicator control circuit for an open or high resistance or short to voltage. If the circuit
checks good continue to the next step.

With the ignition on shift the transmission to neutral and using transfer case output controls
attempt to command the neutral indicator off and on. If the neutral indicator is still
inoperative short to neutral indicator control to ground, if the neutral indicator lights
replace the module, program, and complete the motor learn procedure. If the neutral
indicator is still inoperative replace the switch.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Transfer Case Shift Control Switch Replacement (Without SLT) or Transfer Case
Shift Control Switch Replacement (With SLT)

Control Module References for TCSCM replacement, setup, and programming

Transfer Case High/Low Clutch Reset

DTC B2725

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 B2725 08

Active Transfer Case Mode Switch Circuit

Diagnostic Fault Information

Circuit/System Description

The active transfer case mode switch circuit consists of 5 modes. The transfer case shift control
module supplies 5 volts to the switch through the 5-volt reference circuit. The current travel
through the resistor of the currently active mode. The current is then returned to the transfer case
shift control module through the switch signal circuit. The transfer case shift control module
constantly monitors this signal voltage to determine the condition of the mode switch circuit.
When each of the modes are selected they complete a circuit through their own specific resistor.
The transfer case shift control module continuously monitors the switch input to determine
whether the Neutral, AWD, 2HI, 4HI, or 4LO mode was selected by the driver.

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Invalid

Active Transfer Case Mode
Switch Circuit

DTC B2725

08

DTC B2725

08

DTC B2725
08

DTC B2725

08

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Conditions for Running the DTC

The ignition is ON.

System voltage is 10.5-18 volts.

Conditions for Setting the DTC

The system constantly monitors the voltage on switch signal circuit.

If the system detects a voltage level under 0.38 volts or greater than 4.86 volts for 60
seconds, the DTC is logged.

Action Taken When the DTC Sets

All shifting is disabled.

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 40 consecutive warm up 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

Electrical Information Reference

Circuit Testing

Connector Repairs

Testing for Intermittent Conditions and Poor Connections

Wiring Repairs

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 3023/3024-NQH - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado