GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 STS 🢒 Power and Signal Distribution 🢒 Wiring Systems and Power Management 🢒 DTC B1440

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 B1440 03: Power Mode Master Input Circuits Mismatch Voltage Below Threshold

DTC B1440 08: Power Mode Master Input Circuits Mismatch Signal Invalid

Circuit/System Description

The instrument panel module (IPM) is the power mode master and the remote control door lock receiver (RCDLR) is the backup power mode master. Both modules receive information regarding ignition mode switch position from the ignition mode switch. The ignition mode switch will be monitored only with battery voltage at or above 7 volts to prevent invalid input readings during low voltages encountered during vehicle cranking.

Conditions for Running the DTC

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

Conditions for Setting the DTC
    • The RCDLR input does not match the state of the mode switch received from the IPM.
    • The RCDLR receives a message from the IPM, indicating that a switch has been pressed, without seeing the corresponding input go active.
    • The RCDLR mode data input is active for more than 60 seconds, without seeing the corresponding message from the IPM.

Action Taken When the DTC Sets

The Service Vehicle Soon (SVS) indicator will illuminate. Also, the following scenarios may take place:

    • If the RCDLR senses a change on its ignition mode data input, but does not receive the corresponding message from the IPM, the RCDLR will enable the backup power mode. The backup power mode will be the old power mode. If a second change is sensed by RCDLR on its ignition mode data input, without the corresponding message from the BCM, the backup power mode will be changed accordingly to signal sensed.
    • If the RCDLR receives a message from the IPM, indicating that a switch has been pressed, without sensing the change itself, the setting of the backup power moding will be disabled for the current ignition cycle.

Conditions for Clearing the DTC
    • A current DTC clears when the malfunction is no longer present.
    • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Reference Information

Schematic Reference

Power Distribution Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Power Mode Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification
  1. With a scan tool, verify DTC B1325, B1380, or B1385 are not set.
    2. ⇒If any of the listed DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  2. With a scan tool, verify the power mode parameter matches the each actual power mode state.
    3. ⇒If the parameter does not match, perform the RCDLR circuit testing.
    ⇒If the parameters match, perform the IPM circuit testing.

Circuit/System Testing

IPM

  1. Ignition OFF, disconnect the harness connector at the ignition switch.
  2. Test for B+ between the ignition switch reference voltage circuit terminal F and ground.
    3. ⇒If not the specified value, test the reference voltage circuit for a short to ground or an open/high resistance. If circuit tests normal, replace the IPM.
  3. Test for B+ between the ignition switch reference voltage circuit terminal F and the ignition switch ignition mode data signal circuit terminal E.
    4. ⇒If not the specified value, test the ignition mode data circuit for a short to voltage or an open/high resistance. If circuit tests normal, replace the IPM.
  4. Ignition OFF, disconnect the harness connector at the IPM.
  5. Ignition OFF, with the ignition mode switch held in the ACC position test for 270 ohms of resistance between the IPM ignition mode data signal circuit terminal E and the ignition mode switch voltage reference circuit terminal F.
    6. ⇒If not the specified value, test the circuit for an open/high resistance. If circuit tests normal, replace the ignition mode switch.
  6. Ignition OFF, While switching the ignition mode switch to START, test the ignition mode test for 450 ohms of resistance between the IPM ignition mode data signal circuit terminal E and the ignition mode switch voltage reference circuit terminal F.
    7. ⇒If all circuits test normal, replace the ignition mode switch.
  7. If all circuits test normal, replace the IPM.

RCDLR

  1. Ignition OFF, disconnect the harness connector at the ignition switch.
  2. Ignition ON, Test for B+ between the RCDLR ignition mode data signal circuit and ground.
    3. ⇒If not the specified value, test the ignition mode signal circuit for a short to ground or an open/high resistance. If circuit tests normal, replace the RCDLR.
  3. Verify a test lamp does not illuminate between the ignition mode signal circuit of the RCDLR and ground.
    4. ⇒If the test lamp illuminates, test the ignition mode signal circuit for a short to voltage. If the circuit tests normal, replace the RCDLR.
  4. Test for B+ between the RCDLR ignition mode data signal circuit and the RCDLR ignition mode ground circuit.
    5. ⇒If not the specified value, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the RCDLR.
  5. Ignition OFF, while pressing the ACC/Off button of the ignition mode switch, test for 2000 ohms between the RCDLR ignition mode data signal circuit and the RCDLR ignition mode ground circuit.
    6. ⇒If not the specified value, replace the ignition mode switch.
  6. Ignition OFF, while pressing the Start button of the ignition mode switch, test for less than 1 ohm between the RCDLR ignition mode data signal circuit and the RCDLR ignition mode ground circuit.
    7. ⇒If not within the specified range, replace the ignition mode switch.
  7. If all circuits test normal, replace the RCDLR.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for IPM and RCDLR replacement, setup, and programming