For 1990-2009 cars

### Circuit Description

The accessory switch circuit consists of 4 modes. The transfer case shift control module supplies 5 volts to the switch through the switch signal circuit. The current travels through the resistor of the currently active mode. The current on the switch signal circuit is monitored by the transfer case shift control module. The voltage on the switch signal circuit will vary depending on which mode button is pressed by the driver.

The transfer case shift control module constantly monitors the switch signal circuit to determine the condition of the accessory switch circuit.

When each of the modes are selected they 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 driver.

### 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 5 volt reference circuit.

• | If the system detects a voltage level that is out of range for 10 seconds, 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.

• | 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

• | Check the inline connector C200 for proper connection, bent pins, damage, or corrosion. Refer to Harness Routing Views and Delphi Connectors .

• | Check the transfer case shift control module connectors C1 and C2 for proper connection and bent or corroded pins or terminals. Refer to Repairing Connector Terminals .

• | Check for water leaks at doors and bulkhead areas. Refer to Waterleak Test Preparation .

### Test Description

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

1. This step tests the accessory switch for proper resistance values in all accessory switch states.

2. This step tests the switch signal circuit for proper voltage.

3. This step tests the switch signal circuit for a short to ground, short to voltage, open, or high resistance.

4. This step test the switch signal low circuit for an open, or high resistance.

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? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. With the accessory switch disconnected, connect a DMM between the low reference signal circuit and the 5-volt reference circuit at the switch.
2. Measure the resistance through the accessory switch while pressing and holding each of the mode buttons and comparing values.

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

4 HI: 656.2-669.4 ohms

2 HI: 1.50-1.53 K ohms

Neutral: 1.010-1.031 K ohms

4 LO: 2.32-2.36 K ohms

Normal: 9.00-9.18 K ohms

Go to Step 3

Go to Step 6

3 |

1. Disconnect the accessory switch from the wiring harness.
2. Turn ON the ignition.
3. With a DMM, probe the 5-volt reference circuit.

Was the voltage reading within the specified values?

4.8-5.2 V

Go to Step 5

Go to Step 4

4 | Test the 5-volt reference circuit for a short to voltage, a short to ground, an open, or a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7
5 | Test the switch signal low circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? |  | Go to Step 8 | Go to Step 7
6 | Replace the accessory switch. Refer to Accessory Switch Replacement . Did you complete the repair? | -- | Go to Step 8 | --
7 | Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming. Did you complete the repair? | -- | Go to Step 8 | --
8 |

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