Circuit Description
The body control module (BCM) monitors the Run/Crank voltage signal from the ignition switch. When the vehicle operator places the ignition switch in the RUN or CRANK position, the switch supplies B+ to the BCM Run/Crank voltage input terminal. If this circuit becomes shorted to B+, ground or the circuit opens, DTC B1370 will set.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B1370 Device Ignition 1 Circuit
DTC Symptom | DTC Symptom Descriptor |
|---|---|
01 | Short to Battery |
02 | Short to Ground |
Conditions for Running the DTC
Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
Conditions for Setting the DTC
| • | The BCM detects a short to ground in the Run/Crank voltage circuit when the ignition switch is in RUN or CRANK. |
| • | The BCM detects a short to battery or an open in the Run/Crank voltage circuit when the switch is in the OFF position. |
| • | Any of the conditions above must be present for more than 10 seconds. |
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 GMLAN 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 GMLAN serial data communications circuits. |
Conditions for Clearing the DTC
| • | A current DTC clears when the malfunction is no longer present. |
| • | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
Diagnostic Aids
A history DTC may be caused by an intermittent short or open in the ignition 1 circuit. Refer to Testing for Intermittent Conditions and Poor Connections .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This tests the ignition switch for a short circuit between the 12-volt reference supply circuit and the ignition 1 circuit in the OFF position.
-
This tests the wiring of the ignition 1 circuit for a short to ground or voltage.
-
This tests the ignition switch for a closed circuit between the ignition switch 12-volt reference supply circuit and the Run/Crank voltage circuit in the Run and Crank switch positions. Care must be taken as the engine may crank during this test.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Body Control System Schematics and Power Distribution Schematics Connector End View Reference: Master Electrical Component List | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool display DTC B1370 or DTC B1380 as current? | -- | Go to Step 3 | Go to Diagnostic Aids |
Did you find a short between the 2 circuits? | B+ | Go to Step 4 | Go to Step 5 | |
Did you find and correct the condition? | B+ | Go to Step 9 | Go to Step 7 | |
|
Important: The engine may crank during this procedure.
Can you measure continuity in both Run and Crank? | -- | Go to Step 8 | Go to Step 6 | |
6 | Test the Run/Crank voltage and the ignition switch 12-volt reference supply terminals of the ignition switch harness connector, for intermittent or poor connections, and an open condition. Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
7 | Replace the ignition switch. Refer to Ignition and Start Switch Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- |
8 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC reset? | -- | Go to Step 1 | System OK |
