Diagnostic Instructions

DTC Descriptors

DTC B1370 01: Device Ignition 1 (ON and START) Circuit Short to Battery

DTC B1370 06: Device Ignition 1 (ON and START) Circuit Short to Ground or Open

DTC B1380 01: Device Ignition ACCESSORY Circuit Short to Battery

DTC B1380 06: Device Ignition ACCESSORY Circuit Short to Ground or Open

DTC B1440 00: Power Mode Master Input Circuits Mismatch

DTC B1441 01: Device Ignition OFF, RUN, and CRANK Circuit Short to Battery

DTC B1441 06: Device Ignition OFF, RUN, and CRANK Circuit Short to Ground or Open

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
B+	B1370 06, B1380 06, U0100-U0299, 2, 4	B1370 06, B1380 06, U0100-U0299	--	--
Accessory Voltage	B1370 06, B1380 06, U0100-U0299, 2, 4	B1380 06, 1	B1380 01, P1629, 1	--
Ignition 1 Voltage	B1370 06, B1380 06, U0100-U0299, 2, 4	B1370 06, 1	B1370 01, U0100-U0299, 1, 2	--
Off/Run/Crank Voltage	B1370 06, B1380 06, U0100-U0299, 2, 4	1	1	--
Run/Crank Ignition 1 Voltage	B1428, 3	B1370 06	--	--
Accessory Wakeup Serial Data	U1814, 3	U0100-U0299, P0513 00	--	--
Power Mode Mismatch Scan Tool Does Not Communicate with High Speed GMLAN Device This circuit is a pass through circuit in the BCM and will cause Ign Switch fuse to open. This circuit/condition will cause B+ fuse to open, and may cause a no start condition.

Circuit/System Description

The vehicle 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. The PMM receives the ignition switch signals, and additionally a reference voltage signal from the BCM, through the ignition switch, and back to the BCM. 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 operator's desired power mode and activate specific discrete signals, and serial data messages for the operation of 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 detect from its own connections.

The PMM will activate relays and other direct outputs of the PMM as needed according to the calculated power mode. Some relays controlled by the BCM are switched ignition voltage outputs that are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the B+ circuit fuse to the ignition switch will open.

Conditions for Running the DTC

B1370 01

Ignition switch is in the OFF or ACC positions.

B1370 06, B1380 01, B1441 01, B1441 06

Ignition switch is in the START position.

B1380 06, B1440 00

Ignition switch is in the RUN position.

Conditions for Setting the DTC

B1370 01

Ignition 1 voltage circuit is shorted to voltage.

B1370 06

B1380 01

Accessory voltage circuit is shorted to voltage.

B1380 06

B1440

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 B+ circuit to the ignition switch while the engine is running. An open on the B+ circuit can be caused by a short to ground on any of the circuits listed below:

B1441 01

Off/run/crank voltage circuit is shorted to voltage.

B1441 06

Off/run/crank voltage circuit is open.

Actions Taken When the DTC Sets

Conditions for Clearing the DTC

Diagnostic Aids

Reference Information

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Power Mode Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Verify that the following DTCs are not set: U1814, B1428.

⇒	If either of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. With a scan tool, access BCM, Power Mode data display list 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. The circuits which the individual parameters are related to are in parentheses.

PMM Power Mode Parameters

Ignition Switch Position	Current Power Mode	Ign. Off/Run/Crank (Terminal 5)	Ignition Accessory/Run (Terminal 3)	Ignition Run/Crank (Terminal 2)
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

Circuit/System Testing

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

1. Connect a test lamp between each fuse test terminal of the ignition switch B+ circuit fuse and ground. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the circuits listed below for a short to ground. If all circuits test OK, replace the BCM.

•	B+ terminal 4

•	Ignition terminal 3

•	Ignition terminal 5

•	Ignition terminal 2

•	Ignition voltage terminal BCM terminal 21, X4

2. Disconnect the harness connector at the ignition switch.
3. Connect a test lamp between the B+ circuit terminal 4 and ground. The test lamp should illuminate.

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

Important: The ignition switch component test must be performed before proceeding with this test to verify the integrity of the switch.

4. Perform the ignition switch component test. Verify the switch passes the test.

⇒	If the ignition switch does not test normal, replace the ignition switch.

5. Disconnect the X 1 harness connector at the BCM, test for less than 1.0 volt between the following circuit terminals of the BCM and ground.

•	Ignition terminal 4

•	Ignition terminal 2

•	Ignition terminal 21

•	Ignition terminal 14

⇒	If greater than specified, test the circuit for a short to voltage.

6. Test for less than 1.0 ohm between the BCM and the ignition switch on the circuits listed below:

•	Ignition terminal 4, X1 and ignition switch terminal 6

•	Ignition terminal 2, X1 and ignition switch terminal 5

•	Ignition terminal 21, X1 and ignition switch terminal 3

•	Ignition terminal 14, X1 and ignition switch terminal 2

⇒	If greater than specified, test the circuit for open/high resistance

7. If all circuits test normal, replace the BCM.

Component Testing

Ignition Switch

1. Ignition OFF, disconnect the harness connector at the ignition switch.
2. Verify the resistance between the terminals listed below match for each ignition switch position.

⇒	If not the specified value, replace the ignition switch.

Resistance Test

Ignition Switch Position	Terminals 2 and 4	Terminals 3 and 4	Terminals 4 and 5	Terminals 4 and 6	Terminals 5 and 6
Off Key Out	Infinite	Infinite	Infinite	Infinite	Infinite
Off Key IN	Infinite	Infinite	< 5.0 ohms	Infinite	Infinite
Accessory	Infinite	< 5.0 ohms	Infinite	Infinite	Infinite
Run	< 5.0 ohms	< 5.0 ohms	Infinite	Infinite	< 5.0 ohms
Start	< 5.0 ohms	Infinite	Infinite	Infinite	1275-1325 ohms

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.