Chevrolet Silverado / GMC Sierra. Service manual — part 2874

Diagnostic Fault Information

Circuit/System Description

The transfer case shift control module has an input from incremental sensor which shows the
speed, transfer case range, and direction of the transfer case mode or range shifts. The incremental
sensor is an integral part of the transfer case actuator and can not be replaced independently. The
incremental sensor indicates important information about the speed and direction of the transfer
case two/four wheel drive actuator position. This sensor receives an 8-volt reference signal from
the transfer case control module and gets this data back via the transfer case incremental impulse
signal, as well as the incremental direction signal in order to know the current location.

Conditions for Running the DTC

The ignition is ON.

System voltage is 10.5-18 volts.

Conditions for Setting the DTC

The transfer case control module sees a incremental 8-volt reference signal that is not
between 1.5-8.2 volts indicating a short to ground or open if low and a short to voltage if
high.

The module does not receive a incremental impulse signal voltage between 0.5-4.6 volts.

The incremental low reference circuit has an open or high resistance.

Action Taken When the DTC Sets

All shifting is disabled until the condition no longer exists.

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

Circuit

Short to

Ground

Open/High

Resistance

Short to

Voltage

Signal

Invalid

Incremental Position Sensor
Circuit

DTC C0396

02

DTC C0396

04

DTC C0396

05

DTC C0396
01
DTC C0396
05

-

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

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

Scan Tool Reference

Control Module References for scan tool information

Diagnostic Aids

An open, high resistance, or short to voltage on the incremental sensor direction signal circuit will
cause this DTC to set. If the sensor is determined to be bad the entire transfer case actuator will
have to be replaced as the incremental sensor is part of the actuator and can not be replaced
independently.

Circuit/System Testing

The incremental sensor impulse signal circuit, incremental direction signal circuit, incremental
sensor low reference circuit, and the 8-volt reference circuit will need to be check for a short to
ground, open, high resistance, and a short to voltage using the following steps:

1. Disconnect the connector at the transfer case actuator and check the 8-volt reference signal

on pin G at the transfer case actuator with a DMM, ignition on, the voltage should read 7.8-
8.2 volts.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

If the voltage does not read within the specifications then check the 8-volt reference
circuit for a short to voltage, open, high resistance, or short to ground. If the circuit
checks good and the voltage is out of range replace the transfer case control module,
program, and perform the motor learn procedure. If the circuit checks good continue
to next step.

2. At the transfer case actuator, with a jumper harness short the 8-volt reference circuit pin G

to the incremental impulse signal pin E and note the voltage on the scan tool data display.

If the voltage does not read 7.8-8.2 volts check the incremental impulse signal circuit
for and open, high resistance, short to ground, or short to voltage. If the circuit checks
good then go to the next step.

3. Check the incremental direction circuit for an open, short to ground, high resistance, or a

short to voltage by probing pin F at the transfer case actuator and pin 14 and transfer case
control module connector X2.

If all circuit test good replace the transfer case actuator and perform the motor learn
procedure.

Repair Procedures

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for TCSCM replacement, setup, and programming

Transfer Case High/Low Clutch Reset

Transfer Case Two/Four Wheel Drive Actuator Replacement

DTC C0550

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 C0550 37

Electronic Control Unit Malfunction Watchdog/Safety Failure

DTC C0550 39

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Electronic Control Unit Malfunction Internal Electronic Failure

Diagnostic Fault Information

Circuit/System Description

This DTC indicates and RAM/ROM checksum, a EEPROM failure, or an ECU malfunction due
to an internal microprocessor failure.

Conditions for Running the DTC

The ignition is ON.

System voltage is 10.5-18 volts.

Conditions for Setting the DTC

The EEPROM, RAM and ROM, and ECM Microprocessor do self checks against one another
and the data does not match causing the DTC to set.

Action Taken When the DTC Sets

Shifting is still disabled until the DTC has cleared itself.

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

Circuit

Short to

Ground

Open/High

Resistance

Watchdog/Safety

Failure

Internal

Electronic

Failure

Electronic Control Unit
Malfunction

-

-

DTC C0550 39

DTC C0550

39

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Transfer Case - MP 1625/1626-NQF - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado