Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Scan Tool Data Definitions
The Automatic Transfer Case (ATC) Scan Tool Data Definitions contain a brief description of all ATC related parameters available on the scan tool. The list is in the order it appears on the scan tool.
- ATC Slip Speed
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The scan tool displays a range of 0-8192 RPM. This parameter indicates the RPM difference between the front and rear propshafts.
- Auto 4WD Indicator Light
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The scan tool displays On or Off. This parameter indicates if the Auto 4WD Indicator Light is being commanded by the transfer case shift control module.
- Commanded Mode Indicator
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The scan tool displays a range of Auto 4WD to 4WD Low. This parameter indicates the current mode in which ATC is operating.
- Encoder Circuit A
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The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit A On=<1 Volt, Off=>3 Volts.
- Encoder Circuit B
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The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit B On=<1 Volt, Off=>3 Volts.
- Encoder Circuit C
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The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit C On=<1 Volt, Off=>3 Volts.
- Encoder Circuit P
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The scan tool displays On or Off. This parameter indicates whether transfer case shift control module is sensing voltage on the Encoder Circuit P On=<1 Volt, Off=>3 Volts.
- Encoder Gear Position
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The scan tool displays a range of Auto 4WD to 4WD Low. This parameter indicates the actual transfer case sector shaft position as sensed by the encoder.
- Front Axle Switch
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The scan tool displays Locked or Unlocked. This parameter indicates the feedback states of the front axle switch.
- Front Axle Switch Requested
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The scan tool displays Yes or No. This parameter indicates if the front axle switch has been requested by the transfer case shift control module.
- Front Propshaft Speed
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The scan tool displays a range of 0-8192 RPM. This parameter indicates the rotational speed of the front propshaft.
- GM Part Number
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The scan tool displays an eight-digit number. This parameter indicates the transfer case shift control module GM software number.
- Ignition 3
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The scan tool displays a range of 0- 25.5 volts. This parameter indicates the voltage measured by the transfer case shift control module at its ignition feed.
- Last Adapt Highest PWM
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The scan tool displays a range of 0-100 percent. This parameter indicates the highest duty cycle applied to the ATC motor during the last slip event.
- Mode Switch Selected
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The scan tool displays On or Off. This parameter indicates the ATC mode switch button currently depressed by the driver.
- Neutral Indicator Light
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The scan tool displays On or Off. This parameter indicates if the Neutral Indicator Light is being commanded by the transfer case shift control module.
- Park Switch
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The scan tool displays Open or Closed. This parameter indicates the feedback states of the Park/Neutral Switch.
- Rear Propshaft Speed
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The scan tool displays a range of 0-8192 RPM. This parameter indicates the rotational speed of the rear propshaft.
- Rear Slippage
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The scan tool displays a range of 0- 8192 RPM. This parameter indicates the total slippage of the rear propshaft.
- Service 4WD Lamp
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The scan tool displays On or Off. This parameter indicates if the Service 4WD Lamp is being commanded by the transfer case shift control module.
- Slip Adapt Mode
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The scan tool displays Enabled or Disabled. This parameter indicates if the transfer case shift control module is currently attempting to prevent front to rear propshaft slip.
- Slip Adapt PWM
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The scan tool displays a range of 0-100 percent. This parameter indicates the duty cycle applied to the ATC motor.
- Software ID
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The scan tool displays a 4-digit number. This parameter indicates the transfer case shift control module calibration version number.
- Throttle Anticipation Mode
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The scan tool displays Enabled or Disabled. This parameter changes from Disabled to Enabled when the vehicle starts movement from a stop position, light to heavy throttle is applied, and is currently in AWD mode. Throttle Anticipation Mode helps eliminate the clunking sound normally associated with front axle engagement.
- Total Slippage
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The scan tool displays a range of 0-8192 RPM. This parameter indicates the total slippage of both the front and rear propshafts.
- Throttle Position (TP) Angle
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The scan tool displays a range of 0-100 percent. The TP Angle is computed by the PCM from the TP sensor voltage. The TP Angle should read 0 percent at idle and 100 percent at Wide-Open Throttle (WOT).
- Transfer Case Lock
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The scan tool displays Enabled or Disabled. This parameter indicates if the transfer case shift control module is commanding the transfer case motor brake On.
- 2WD High Indicator Light
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The scan tool displays On or Off. This parameter indicates if the 2WD High Indicator Light is being commanded by the transfer case shift control module.
- 4WD High Indicator Light
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The scan tool displays On or Off. This parameter indicates if the 4WD High Indicator Light is being commanded by the transfer case shift control module.
- 4WD Lamp Open
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The scan tool displays Yes or No. This parameter indicates if the 4WD Lamp circuit is open or shorted to ground.
- 4WD Lamp Shorted
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The scan tool displays Yes or No. This parameter indicates if the 4WD Lamp circuit is shorted to voltage.
- 4WD Low Indicator Light
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The scan tool displays On or Off. This parameter indicates if the 4WD Low Indicator Light is being commanded by the transfer case shift control module.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.