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: Power Mode Master Input Circuits MismatchDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Accessory Voltage | 2* | 1* | 1* | -- |
Ignition 0 Voltage | 3* | 1* | 1* | -- |
Ignition 1 Voltage | 4* | 1* | 1* | -- |
Ignition 3 Voltage | 5* | 1* | 1* | -- |
Battery Positive Voltage (IGN A fuse) | 6* | 1* | -- | -- |
Battery Positive Voltage (IGN B fuse) | 7* | 1* | -- | -- |
Ignition switch voltage output circuits | 8* | 1** | 1** | -- |
1. Power Mode Mismatch--Different specific symptoms may occur depending on the vehicle operating conditions when the fault occurred. 2. TBC ACC fuse will open. 3. TBC IG fuse will open. 4. TBC IGN 1 fuse will open. 5. TBC RUN fuse will open. 6. IGN A fuse will open. 7. IGN B fuse will open. 8. These circuits will open either the IGN A or the IGN B fuse. * Depending on the vehicle conditions when the fault occurs a DTC B1440 may set and the vehicle may not start. ** These circuits are between the ignition switch and the fuse block prior to the BCM (TBC) fuses. | ||||
Circuit/System Description
This vehicles power mode master (PMM) is the body control module (BCM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination of the power mode. There are redundancies within the PMM system that can allow operation of certain subsystems when there are faults in the ignition switch circuits. Other information such as serial data input from other modules and DTCs is also used to determine what power mode signals and information is transmitted by the PMM. The BCM logic uses all this information to identify the operators desired power mode and activate specific discrete signals, and serial data messages for the operation of many different subsystems as necessary. Other modules which have switched voltage inputs may operate in a default mode if the PMM serial data message does not match what the individual module can see from its own connections. The PMM will activate relays and other direct outputs of the PMM as needed according to the calculated power mode.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Power Mode Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for Scan Tool Information
Circuit/System Verification
With a scan tool, access the power mode parameters and compare all parameters listed with the corresponding ignition key position. The PMM Power Mode Parameters table below illustrates the correct state of these input parameters in correspondence to the ignition switch position.
| ⇒ | If any parameter is incorrect in any key position refer to Circuit/System Testing. |
Ignition Switch Position | System Power Mode | Ignition 0 Voltage | Ignition 1 Voltage | Ignition 3 Voltage | Ignition Accessory |
|---|---|---|---|---|---|
Off | Off Awake or RAP | Off | Off | Off | Inactive |
Unlock | Unlock or RAP Unlock | On | Off | Off | Inactive |
Accessory | Accessory | On | Off | Off | Active |
Run | Run | On | On | On | Active |
Start | Crank | On | On | Off | Inactive |
Circuit/System Testing
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
If a circuit fault exists in the BCM body wiring harness extension harness it must be replaced.- Ignition OFF, disconnect the harness connector at the ignition switch.
- Verify that a test lamp illuminates between the B+ circuit terminal B and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal F and ground.
- Perform the ignition switch component test. The test should pass.
- Ignition OFF, connect the harness connector at the ignition switch, and disconnect the X 3 harness connector at the BCM.
- Verify a test lamp illuminates between ignition 1 voltage circuit terminal A19 and ground only in the RUN and START ignition switch positions.
- Verify a test lamp illuminates between accessory voltage circuit terminal B15 and ground only in the ACCY and RUN ignition switch positions.
- Verify a test lamp illuminates between ignition 0 voltage circuit terminal A18 and ground only in the UNLOCK, ACCY, RUN and START ignition switch positions.
- Verify a test lamp illuminates between ignition 3 voltage circuit terminal A20 and ground only in the RUN ignition switch position.
- If all circuits test normal, replace the BCM.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or a short to ground, and test the ignition switch ignition voltage output circuits for a short to ground. |
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or a short to ground, and test the ignition switch ignition voltage output circuits for a short to ground. |
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. |
| ⇒ | If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp illuminates when it should not, test the circuit between the BCM and the ignition switch for a short to voltage. If the circuit tests normal, test or replace the ignition switch. |
| ⇒ | If the test lamp does not illuminate, test the circuit between the BCM and the ignition switch for a short to a short to ground or an open/high resistance. If the circuit tests normal, test or replace the ignition switch. |
Component Testing
Ignition Switch
- Ignition OFF, disconnect the harness connector at the ignition switch.
- Using the Resistance Test table below, check the resistance between the terminals of the ignition switch listed in each switch position.
Ignition Switch Position | Terminals B and A | Terminals B and C | Terminals F and E | Terminals F and G | Terminals F and D |
|---|---|---|---|---|---|
Off | Infinite | Infinite | Infinite | Infinite | Infinite |
Accessory | < 5.0 Ohms | Infinite | < 5.0 Ohms | Infinite | Infinite |
Run | < 5.0 Ohms | < 5.0 Ohms | < 5.0 Ohms | < 5.0 Ohms | Infinite |
Start | Infinite | < 5.0 Ohms | < 5.0 Ohms | Infinite | < 5.0 Ohms |
| ⇒ | If any reading is not as specified, replace the ignition switch. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for module replacement, setup, and programming |
