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

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Accessory Voltage	B1370 06, B1380 06, U0100-U0299, 2	B1380 06, 1	B1380 01, P1629, 1	--
Battery Positive Voltage	B1370 06, B1380 06, U0100-U0299, 2	B1370 06, B1380 06, U0100-U0299	--	--
Ignition 1 Voltage	B1370 06, B1380 06, U0100-U0299, 2	B1370 06, 1	B1370 01, U0100-U0299, 1, 2	--
Off/Run/Crank Voltage	B1370 06, B1380 06, U0100-U0299, 2	1	1	--
Run Crank Relay Coil Control	B1428 00	B1370 06	--	--
1. Power Mode Mismatch 2. Scan Tool Does Not Communicate with High Speed GMLAN Device

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. 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 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. Several relays controlled by the BCM are switched ignition voltage outputs the are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the fuse to the ignition switch will open.

Some system functions may operate one time and not the next with a specific fault in the ignition switch circuits depending on the vehicle operating conditions when the fault occurred. Some examples are as follows:

Vehicle Conditions

System Action

Conditions for Running the DTC

B1370 01

Ignition switch is in the OFF or ACC positions.

B1370 06

Ignition switch is in the START position.

Conditions for Setting the DTC

B1370 01

Ignition 1 voltage circuit is shorted to voltage for more than 2 seconds.

B1370 06

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 the following DTCs are not set: U1814, B1428.

⇒	If either of the DTCs are set, refer to 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 (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

Circuit/System Testing

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

1. Verify the Ign Switch fuse is not open.

⇒	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

2. Disconnect the Key In Switch harness connector.
3. Ignition OFF, test for less than 5 ohms 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

Important: 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 volt between the following circuits of the BCM and ground.

•	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.

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

•	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.

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 ohms 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, check the resistance between the pins of the ignition switch listed in 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 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

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.