For 1990-2009 cars

### 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: ATC Mode Switch Circuit Malfunction

### Circuit/System Description

The automatic transfer case (ATC) accessory switch consists of 4 modes. The transfer case shift control module supplies 5 volts to the ATC accessory switch mode buttons. A signal switch low circuit completes the circuit back to the transfer case shift control module. The voltage on the switch signal circuit will vary depending on which button is pressed. When selected, each mode will complete a circuit through their own specific resistor. The transfer case shift control module continuously monitors the switch signal circuit to determine whether the Neutral, 2HI, 4HI, or 4LO mode was selected by the vehicle operator.

### Conditions for Running the DTC

• | The ignition is ON.

• | The system voltage is 9-16 volts.

### Conditions for Setting the DTC

• | The voltage detected on the switch signal circuit is not within a specified range.

• | The condition is present for more than 10 seconds.

### Action Taken When the DTC Sets

• | All transfer case shifting is disabled.

• | The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

• | The transfer case defaults to 4WD high mode.

### Conditions for Clearing the DTC

• | The transfer case shift control module will clear the current DTC if the condition for setting the DTC is not currently present.

• | A history DTC will clear after 100 consecutive ignition cycles without a fault present.

• | History DTCs can be cleared using a scan tool.

### Diagnostic Aids

A low battery condition or charging system that is faulty could set this DTC. Refer to Battery Inspection/Test and Charging System Test .

### Reference Information

#### Schematic Reference

Transfer Case Control Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transfer Case Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, engine OFF, with a scan tool command each mode function switch ON one at a time, on the instrument panel accessory switch. Each mode button indicator light should illuminate.
2. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records Data.

### Circuit/System Testing

Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.

1. Ignition OFF, disconnect the accessory switch electrical connector.
2. Verify that a test lamp illuminates between B+ and terminal H of the accessory switch electrical connector.

⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, engine OFF, verify that a test lamp illuminates between terminal A and ground.

⇒ | If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance.

4. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal M and ground.

⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the transfer case shift control module.

⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the transfer case shift control module.

5. Ignition OFF, install a 3 A fused jumper wire between the switch signal low circuit terminal N and the 5-volt reference circuit terminal M at the accessory switch.
6. Disconnect the transfer case shift control module connector C1.
7. Ignition ON, verify 4.8-5.2 volts is present at connector C1 terminal 14.

⇒ | If less than the specified range, test the switch signal low circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the transfer case shift control module.

⇒ | If greater than the specified range, test the switch signal low circuit for a short to voltage. If the circuit tests normal, replace the transfer case shift control module.

8. If all circuit tests normal, replace the accessory switch.

### Component Testing

Important: You must perform the Circuit/System Testing before proceeding to Component Testing.

1. Disconnect the accessory switch electrical connector.
2. Connect a DMM between the switch signal low circuit and the 5-volt reference circuit at the accessory switch.
3. Measure the resistance while pressing and holding each of the mode buttons. The resistance values should be within the specified ranges:

• | 4HI: 656.2-669.4 ohms

• | 2HI: 1.50-1.53 K ohms

• | Neutral: 1.010-1.031 K ohms

• | 4LO: 2.32-2.36 K ohms

• | Normal: 9.00-9.18 K ohms

⇒ | If the resistance values are not within the specified range, replace the accessory switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Accessory Switch Replacement

• | Control Module References for transfer case control module replacement, setup, and programming.