GM Service Manual Online
For 1990-2009 cars only

Important: Ensure that the scan tool you are using is functioning properly and has the latest software. Use of a malfunctioning scan tool or one that has old software can result in misdiagnosis and unnecessary parts replacement. The transfer case Scan Tool Data List contains all the automatic transfer case (ATC) related parameters that are available on the scan tool. The Scan Tool Data List is arranged in alphanumeric order.

Use the transfer case Scan Tool Data List only after the following is determined:

    • The Diagnostic System Check - Vehicle has been completed.
    • There are no diagnostic trouble codes (DTCs) set.
    • Transfer case diagnostic tables indicate the system is functioning properly.

Scan tool values from a properly operating system may be used for comparison with the transfer case system you are diagnosing. The transfer case Scan Tool Data List represents values recorded under the following conditions:

    • The engine is at idle.
    • The throttle is closed.
    • The transmission is in PARK or NEUTRAL.
    • The accessories are OFF.
    • The ATC is in 2WD HI.

Only the parameters listed below are referenced in this service manual for use in diagnosis. If all values are within the typical range described below, refer to Testing for Intermittent Conditions and Poor Connections for further diagnosis.

Scan Tool Parameter

Data List

Units Displayed

Typical Data Value

2WD High Indicator Light

Data Display

On/Off

On

4WD High Indicator Light

Data Display

On/Off

Off

4WD Low Active

Data Display

Yes/No

No

4WD Low Indicator Light

Data Display

On/Off

Off

Battery Voltage

Data Display

Volts

Battery Voltage

Clutch Pedal Engaged

Data Display

Yes/No

No

Encoder Gear Position

Data Display

2WD/Neutral/4WD HI/4WD LO

2WD

Encoder Return Voltage

Data Display

Volts

0-5 V

Encoder Supply Voltage

Data Display

Volts

0-7.5 V

Front Axle Requested

Data Display

Yes/No

No

Front Axle Switch

Data Display

Locked/Unlocked

Unlocked

Ign. Cycles Since Last Current DTC

Data Display

Number

Varies

Mode Switch Return Voltage

Data Display

Volts

0-5 V

Mode Switch Selected

Data Display

On/Off

Off

Motor A Current

Data Display

mA

Varies

Motor B Current

Data Display

mA

Varies

Neutral Indicator Light

Data Display

On/Off

Off

Service 4WD Lamp

Data Display

On/Off

Off