B1370

DTC B1370

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC B1370
- Device Ignition 1 (ON and START) Circuit




Diagnostic Fault Information






Circuit Description

The body control module (BCM), monitors the ignition 3, crank voltage, and ignition 1 circuits from the ignition switch. The BCM uses the sequence that the signals appear and their voltage levels to determine the power mode called for by the vehicle operator using the ignition switch. A 12 volt reference voltage is supplied by the BCM to the ignition switch over a discrete circuit. The ignition switch uses this voltage for power mode signal discrimination. When the operator places the ignition switch in the Run or Start position, the ignition 1 circuit is delivers the signal to the BCM.


Conditions for Running the DTC

* The BCM must be powered and must detect a change in the ignition switch circuit states.
* The vehicles battery must be fully charged.



Conditions for Setting the DTC

The BCM detects that the ignition 1 signal is shorted to ground, voltage, or open for more than 10 seconds in the current ignition cycle.


Action Taken When the DTC Sets

* The BCM stores DTC to memory.
* 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 class 2 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 class 2 serial data communications circuits.



Conditions for Clearing the DTC

* A current DTC clears on the next malfunction free cycle.
* A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.



Reference Information
Schematic Reference

Power Moding Schematics (Power Moding Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Power Mode Description and Operation (Power Mode Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for Scan Tool Information


Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X1 of the ignition switch.
2. Verify that a test lamp illuminates between the 12 volt reference circuit terminal A and ground.

• If the test lamp does not illuminate, test the 12 volt reference circuit for a short to ground or an open/high resistance, and test the ignition 1 voltage circuit for a short to ground. If the circuits test normal, replace the BCM.

3. Disconnect the harness connector X1 of the BCM. Connect the harness connector X1 of the ignition switch.
4. Test for less then 1 ohm of resistance between the 12 volt reference circuit terminal 25 and ignition 1 voltage circuit terminal 22 with the ignition switch in the RUN and START positions.

• If greater than the specified range in either position, test the ignition 1 voltage circuit for open/high resistance. If the circuit tests normal, test or replace the ignition switch.

5. Connect a 3 amp fused jumper between B+ and the 12 volt reference circuit terminal 25 of BCM harness connector X1.
6. With the ignition switch in the OFF and ACCY positions, test for less than 1 volt between ignition 1 voltage circuit terminal 22 of BCM connector X1 and ground.

• If greater than the specified range, test the ignition 1 voltage circuit for a short to voltage. If the circuit tests normal, test or replace the ignition switch.

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



Component Testing
Ignition Switch

Using the Resistance Test below, check the resistance between the terminals of the ignition switch listed in each switch position listed.

If any reading is other than specified, replace the ignition switch.







Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Control Module References (Programming and Relearning) for module replacement, setup, and programming
* Ignition and Start Switch Replacement (Service and Repair)