Circuit Description
The body control module (BCM), monitors the ignition inputs OFF, ignition 3, crank and ignition 1 supplied 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 Start position, the Crank circuit delivers the signal to the BCM.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC B1385 Device Ignition START Circuit
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 crank 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 engine will not crank. |
| • | 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. |
Diagnostic Aids
A history DTC maybe caused by an intermittent short or open in the crank 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 step tests the ignition switch for a short circuit between the 12-volt reference supply circuit and the crank circuit in the OFF position.
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This step tests the wiring of the crank circuit for a short to ground or voltage.
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This step tests the ignition switch for a closed circuit between the ignition switch 12-volt reference supply circuit and the crank circuit in the Crank switch position. Care must be taken as the engine may crank during this test.
Step | Action | 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 to DTC B1385 as current? | Go to Step 3 | Go to Diagnostic Aids |
Did you find a short between the 2 circuits? | Go to Step 4 | Go to Step 5 | |
Did you find and correct the condition? | Go to Step 9 | Go to Step 7 | |
|
Important: The engine may crank during this procedure.
Can you measure continuity in Crank? | Go to Step 8 | Go to Step 6 | |
6 | Test the crank 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 |
