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 00: Power Mode Master Input Circuits MismatchDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
B+ | B1440 00 | B1440 00 | -- | -- |
Off/Run/Crank Voltage | B1440 00 | B1440 00, B1441 06 | B1440 00, B1441 01 | -- |
Ignition 1 Voltage | B1440 00 | B1370 06 | B1370 01, B1440 00 | -- |
Accessory Voltage | B1440 00 | B1380 06 | B1380 01 | -- |
Circuit/System Description
The body control module (BCM) monitors the ignition inputs ignition off/run/crank voltage, ignition 1 voltage and the accessory voltage signals supplied from the ignition switch. The ignition key resistor signal circuit provides 5-volt reference from the BCM to the ignition switch. The BCM uses the sequence that the signals appear, their voltage levels, the engine run flag (ERF) status and the remote start status to determine the power mode.
Conditions for Running the DTC
Ignition switch is in the RUN position.
Conditions for Setting the DTC
| • | BCM senses an open or short to voltage on the off/run/crank voltage circuit when both ignition accessory/run and ignition run/crank parameters are active. |
| • | BCM senses an open on the battery positive voltage circuit while engine is running. An open on the battery voltage circuit can be caused by a short to ground on any of the following circuits: |
| - | Battery positive voltage |
| - | Accessory voltage |
| - | Ignition 1 voltage |
| - | Off/run/crank voltage |
Action Taken When the DTC Sets
| • | The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the GMLAN serial data communications circuits. |
| • | The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the GMLAN serial data communications circuits. |
| • | The vehicle may not start. |
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 of 50, without a repeat of the malfunction. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Retained Accessory Power Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information.
Circuit/System Verification
With a scan tool, verify the Power Mode data display parameters match the chart below. The PMM Power Mode Parameters table below illustrates the correct state of these input parameters (circuits) in correspondence to the ignition switch position. The circuits which the individual parameters are related to are in parentheses.
Ignition Switch Position | Current Power Mode | Ignition Off/Run/Crank (Off/Run Crank Voltage Circuit) | Ignition Accessory/Run (Accessory Voltage Circuit) | Ignition Run/Crank (Ignition 1 Voltage Circuit) |
|---|---|---|---|---|
Off Key Out | Off | Key Out/ACC | Inactive | Inactive |
Off Key IN | Off | Key In/Off | Inactive | Inactive |
Accessory | Accessory | Key Out/ACC | Active | Inactive |
Run | Run | Run | Active | Active |
Start | Crank Request | Crank | Inactive | Active |
| ⇒ | If any parameters are incorrect in any key position, proceed to the Circuit/System Testing. |
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
- Verify the Ign Switch fuse is not open.
- Disconnect the harness connector at the Key In Switch.
- Ignition OFF, test for less than 5 ohms of resistance between the Key In Switch terminal 1 and terminal 2.
- Ignition OFF, key out, test for infinite resistance between the Key In Switch terminal 1 and terminal 2.
- Connect the harness connector at the Key In Switch.
- Disconnect the harness connector at the ignition switch.
- Verify a test lamp illuminates between the battery positive voltage circuit of the ignition switch and ground.
- Perform the ignition switch component test. The test should pass.
- Ignition OFF, disconnect the X1 harness connector at the BCM.
- With a DMM, test for less than 1 volt between the following circuits of the BCM and ground.
- Ignition key out, with a DMM, test for less than 1 volt between the following circuits of the BCM and ground.
- Disconnect the harness connector at the Key In Switch.
- Install a jumper wire between the Key In Switch terminal 1 and terminal 2.
- Ignition OFF, test for less than 5 ohms of resistance between the BCM and the ignition switch on the following circuits.
- Ignition OFF, test for infinite resistance between the BCM ignition key resistor signal circuit terminal 4 and ground.
- If all circuits test normal, replace the BCM.
| ⇒ | If the fuse is open, test the following circuits for a short to ground, if all circuits test OK, replace the BCM. |
| • | Ignition Switch Battery positive voltage - Terminal 1 |
| • | Ignition Switch Ignition 1 voltage - Terminal 2 |
| • | Ignition Switch Accessory voltage - Terminal 4 |
| • | Ignition Switch Off/Run crank voltage - Terminal 5 |
| ⇒ | If greater than the specified range, replace the Key In Switch. |
| ⇒ | If less than the specified range, replace the Key In Switch. |
| ⇒ | If not the specified value, test the circuit for an open/high resistance |
Important: The ignition switch component test must be preformed before proceeding with this test to verify the integrity of the switch.
| ⇒ | If the ignition switch fails, replace the ignition switch. |
| • | Ignition key resistor signal Terminal 4 |
| • | Off/Run crank Terminal 2 |
| • | Accessory voltage Terminal 21 |
| • | Ignition 1 voltage Terminal 14 |
| ⇒ | If not the specified range, test the circuit for a short to voltage. |
| • | Ignition key resistor signal Terminal 4 |
| • | Off/Run crank Terminal 2 |
| • | Accessory voltage Terminal 21 |
| • | Ignition 1 voltage Terminal 14 |
| ⇒ | If not the specified range, test the circuit for a short to voltage. |
| • | Ignition key resistor signal Terminal 4 and Terminal 6 |
| • | Off/Run crank Terminal 2 and Terminal 5 |
| • | Off/Run crank Terminal 2 and Terminal 3 |
| • | Accessory voltage Terminal 21 and Terminal 4 |
| • | Ignition 1 voltage Terminal 14 and Terminal 2 |
| ⇒ | If not the specified range, test the circuit for open/high resistance. |
| ⇒ | If not the specified value, test the signal circuit for a short to ground. |
Component Testing
Ignition Switch
Using the Resistance Test below, check the resistance between the pins of the ignition switch listed in each switch position listed.
| ⇒ | If any reading is other than specified, replace the ignition switch. |
Ignition Switch Position | Pins 1 and 4 | Pins 1 and 2 | Pins 1 and 3 | Pins 5 and 6 |
|---|---|---|---|---|
Off Key Out | Infinite | Infinite | Infinite | Infinite |
Off Key IN | Infinite | Infinite | < 5.0 ohms | Infinite |
Accessory | < 5.0 ohms | Infinite | Infinite | Infinite |
Run | < 5.0 ohms | < 5.0 ohms | Infinite | < 5.0 ohms |
Start | Infinite | < 5.0 ohms | Infinite | 1275-1325 ohms |
Key In Switch
- Ignition OFF, disconnect the harness connector at the Key In Switch.
- Test for infinite resistance between the signal terminal 1 and the control circuit terminal 2 with the switch in the open position.
- Test for less than 1 ohm of resistance between the signal terminal 1 and the control circuit terminal 2 with the switch in the closed position.
| ⇒ | If not the specified value, replace the key in switch. |
| ⇒ | If not the specified value, replace the key in switch. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for BCM replacement, setup, and programming |
