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+ - Terminal 1	B1370 06, B1380 06, U0100-U0299, 1, 5, 6	B1370 06, B1380 06, U0100-U0299, 1	--	--
Ignition - Terminal 2	B1370 06, B1380 06, U0100-U0299, 1, 5, 6	B1370 06, 1	B1370 01, U0100-U0299, 1, 6	--
Ignition - Terminal 4	B1370 06, B1380 06, U0100-U0299, 1, 5, 6	B1380 06, 1	B1380 01, P1629, 1	--
Ignition - Terminal 5	B1370 06, B1380 06, U0100-U0299, 1, 5, 6	1	1	--
Ignition Key Resistor Signal	1	1	1	--
Ignition Voltage -  BCM Terminal 21 X4	B1428 00, 4	2	3	--
Accessory Wakeup Serial Data, BCM Terminal 19 X4	U1814, 4	U0100-U0299, P0513 00	--	--
Power Mode Mismatch. Different specific symptoms may occur depending on the vehicle operating conditions when the fault occurred. Vehicle will not start and will set DTC B1370 06 in SIR. The engine will continue to run after ignition key is removed. This circuit is a pass through circuit in the BCM and will cause the B+ fuse to open. This circuit/condition will cause the B+ fuse to open, and may cause a no start condition. Scan Tool Does Not Communicate with High Speed GMLAN Device

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 circuits to the BCM. The BCM logic uses the ignition switch positions 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, B1380 01

Ignition switch is in the RUN or CRANK positions.

B1370 06, B1380 06

Ignition switch is in the RUN or ACCESSORY positions.

B1440 00

Ignition switch is in the RUN position.

B1441 01, B1441 06

Ignition switch is in the CRANK position.

Conditions for Setting the DTC

B1370 01

Ignition circuit is shorted to voltage.

B1370 06

B1380 01

Accessory circuit is shorted to voltage.

B1380 06

B1440 00

BCM detects an open or short to voltage on the off/run/crank signal circuit when both ignition ACCESSORY/RUN and ignition RUN/CRANK parameters are active.

BCM detects an open on the B+ circuit to the ignition switch while the engine is running.

B1441 01

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

B1441 06

Off/run/crank signal 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

Retained Accessory Power Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Verify that DTC U1814 or B1428 is not set.

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

2. 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.

PMM Power Mode Parameters

Ignition Switch Position	Current Power Mode	Ignition Off/Run/Crank (Ignition Switch, Terminal 5)	Ignition Accessory/Run (Ignition Switch, Terminal 4)	Ignition Run/Crank (Ignition Switch, 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. Verify the B+ fuse to the ignition switch is not open.

⇒	If the fuse is open, test the following circuits at the ignition switch for a short to ground, if all circuits test OK, replace the BCM.

•	B+ - Terminal 1

•	Ignition - Terminal 2

•	Ignition Switch - Terminal 4

•	Ignition Switch - Terminal 5

•	Ignition - BCM terminal 19, X4

•	Accessory Wakeup Serial Data - BCM terminal 21, X4

2. Disconnect the Key In Switch harness connector.
3. Ignition OFF, test for less than 5 Ω of resistance between the Key In Switch terminal 1 and terminal 2.

⇒	If greater than the specified range, replace the Key In Switch.

4. Ignition OFF, key out, test for infinite resistance between the Key In Switch terminal 1 and terminal 2.

⇒	If less than the specified range, replace the Key In Switch.

5. Connect the Key In Switch harness connector.
6. Disconnect the ignition switch harness connector.
7. Test for battery positive voltage between the battery positive voltage circuit of the ignition switch and ground.

⇒	If not the specified value, test the circuit for an open/high resistance.

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

8. Perform the ignition switch component test. The test should pass.

⇒	If the ignition switch fails, replace the ignition switch.

9. Ignition OFF, disconnect BCM connector X1, test for less than 1 V between the following circuits of the BCM and ground.

•	terminal 2

•	terminal 4

•	terminal 14

•	terminal 21

⇒	If not the specified range, test the circuit for a short to voltage.

10. Ignition key out, test for less than 1 V between the following circuits of the BCM and ground.

•	terminal 2

•	terminal 4

•	terminal 14

•	terminal 21

⇒	If not the specified range, test the circuit for a short to voltage.

11. Disconnect the Key In Switch harness connector.
12. Install a jumper wire between the Key In Switch terminal 1 and terminal 2.
13. Test for less than 5 Ω of resistance between the BCM and the ignition switch on the following circuits.

•	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.

14. Test for infinite resistance between the BCM ignition key resistor signal circuit terminal 4 and ground.

⇒	If not the specified value, test the signal circuit for a short to ground.

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

Component Testing

Ignition Switch

Using the Resistance Test below, verify the resistance between the pins of the ignition switch match the chart below while cycling the key to each switch position listed.

Resistance Test

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 Ω	Infinite
Accessory	< 5.0 Ω	Infinite	Infinite	Infinite
Run	< 5.0 Ω	< 5.0 Ω	Infinite	< 5.0 Ω
Start	Infinite	< 5.0 Ω	Infinite	1275-1325 Ω

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.