GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 4WD 🢒 Restraints 🢒 SIR 🢒 DTC B2725

Circuit Description

The range/mode switch circuit consists of 4 normally open switches. The transfer case shift control module supplies a regulated 8 volts DC to the switch through the 8-volt reference circuit. The current travel through a 9.09 K ohms resistor located inside the switch. Then returns current 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. If no buttons are pressed, and the transfer case shift control module detects a voltage level outside the possible range approximately -0.5 to +1.0 volts for longer than 5 minutes, the transfer case shift control module will set this DTC or if a button is held down or sticks for a period longer than 5 minutes.

When each of the switches is depressed they will complete a circuit through their own specific resistor. The transfer case shift control module continuously monitors the switch input to determine whether the 4HI, AUTO 4WD, 2HI, and 4LO button selections are made by the driver. Neutral may be obtained if the following conditions are met:

    • The engine is running.
    • The automatic transmission is in Neutral or the clutch pedal is depressed on a manual transmission application.
    • The vehicle speed is below 5 km/h (3 mph).
    • The transfer case is in the 2HI mode.

Once these conditions have been met, pressing and holding both the 2HI and 4LO buttons for 10 seconds will shift the transfer case into Neutral, turning on the red Neutral indicator lamp.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2725 ATC Mode Switch Circuit Malfunction

Conditions for Running the DTC
    • The ignition is ON.
    • The system voltage is 9-16 volts.

Conditions for Setting the DTC
    • The system constantly monitors the voltage on the switch signal circuit.
    • If the system detects a voltage level outside the possible range produced when no buttons are depressed, approximately -0.5 to +1.0 volts, 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 current DTC if the condition for setting the DTC no longer exists.
    • A history DTC clears after 100 consecutive ignition cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests for proper operation of the transfer case mode select switch.

    2.

  2. This step tests for proper voltage supply to the transfer case mode select switch.

    3.

  3. This step tests the transfer case mode select switch for proper resistance values in all switch states.

    4.

  4. This step tests the switch signal circuit for a short to voltage.

    5.

  5. This step tests the switch signal circuit for an open or a short to ground.

    6.

  6. This step tests the switch signal circuit for a short to the 8 volt Reg circuit.

    7.

  7. This step determines whether the 8 volt Reg circuit is greater than or less than the specified voltage.

    8.

  8. This step tests the 8 volt Reg circuit for a short to voltage.

    9.

  9. This step tests the 8 volt Reg circuit for a short to ground.

Step

Action

Values

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important: Neutral Range is only obtained by pressing and holding both the 2 HI and the 4 LO buttons simultaneously for 10 seconds. Refer to Circuit Description.

  1. Install a scan tool.
  2. Start the engine.
  3. Place the transmission into Neutral.
  4. Set the parking brake.
  5. With a scan tool, observe the Mode Switch Selected parameter.
  6. Depress and hold each of the Mode buttons while viewing the scan tool mode switch selected parameter.

Does the scan tool indicate that the mode switch selected data parameter is indicating the correct state?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the transfer case shift control switch.
  3. Turn the ignition ON, with the engine OFF.
  4. Measure the voltage from the 8-volt reference circuit to a good ground.

Is the voltage within the specified values?

7-9 V

Go to Step 4

Go to Step 8

4

  1. Connect a DMM between the transfer case shift control switch signal circuit and the 8-volt reference circuit at the switch.
  2. Measure the resistance through the switch, while depressing the mode buttons and comparing the values.

Does the DMM indicate all resistance values within the specified ranges?

Normal: 8.63-9.54 K ohms

Auto 4 WD: 61.7-68.1 ohms

4 HI: 656-670 ohms

2 HI: 1.50-1.53 K ohms

4 LO: 2.32-2.37 K ohms

Neutral: 1.015-1.035 K ohms

Go to Step 5

Go to Step 11

5

  1. Turn the ignition OFF.
  2. Disconnect the transfer case shift control module.
  3. Turn the ignition ON, with the engine OFF.
  4. Test the switch signal circuit for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 6

6

Test the switch signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 7

7

Test the switch signal circuit for a short to the 8-volt reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

8

Was the voltage measured in Step 3 greater than the specified value?

9 V

Go to Step 9

Go to Step 10

9

  1. Turn the ignition OFF.
  2. Disconnect the transfer case shift control module.
  3. Turn the ignition ON, with the engine OFF.
  4. Test the 8-volt reference circuit for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10

  1. Turn the ignition OFF.
  2. Disconnect the transfer case shift control module.
  3. Turn the ignition ON, with the engine OFF.
  4. Test the 8-volt reference circuit for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the transfer case shift control switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you find and correct the condition?

--

Go to Step 13

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12

Replace the transfer case shift control module. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you find and correct the condition?

--

Go to Step 13

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13
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC set?

--

Go to Step 2

System OK