Circuit Description
The body control module (BCM) monitors the inputs Off/Run/Crank, Run/Crank and the Accessory signals 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 and the ignition switch. A +5 volt regulated voltage source is supplied by the BCM to the ignition switch over a discrete circuit. The ignition switch uses this voltage for Off/Run/Crank signal discrimination and the anti theft reference voltage generation. A constant battery positive voltage is also supplied to the ignition switch to generate the Run/Crank, Accessory and Key In signals. These signals are transmitted to the BCM over discrete circuits. The Accessory signal is also routed to the vehicles electronic control unit (ECU) and is used as a digital signal reference. The Run/Crank signal in conjunction with being supplied to the BCM is sent directly to the Run/Crank relay control coil.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC B1441 Device Ignition OFF, RUN, and CRANK Circuit |
| • | DTC B1442 Device Ignition OFF, RUN, and CRANK Circuit Low |
| • | DTC B1443 Device Ignition OFF, RUN, and CRANK Circuit High |
Conditions for Running the DTC
| • | The BCM must be powered and must detect a change in the ignition switch circuit states. |
| • | The vehicle battery must be fully charged. |
Conditions for Setting the DTC
DTC B1441
The BCM does not detect the Off/Run/Crank signal for more than 10 seconds in the current ignition cycle.
DTC B1442
The BCM detects that the Off/Run/Crank signal is shorted to ground for more than 10 seconds in the current ignition cycle.
DTC B1443
The BCM detects that the Off/Run/Crank signal is shorted to B+ for more than 10 seconds in the current ignition cycle.
Action Taken When the DTC Sets
| • | The BCM stores the 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 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 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 Off/Run/Crank circuit. |
| • | The BCM supplies a +5-regulated voltage source to the ignition switch to develop the Off/Run/Crank signal. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step test for an open circuit in the wiring between the ignition switch and the BCM.
-
This tests the +5-volt regulated supply in the BCM.
-
This tests the ignition switch for a closed circuit between the +5-volt regulated supply and the Off/Run/Crank circuit.
-
This tests the wiring of the Off/Run/Crank circuit for a shot to ground or voltage. This test may be expedited using the DTC to direct the testing. DTC B1442 short to ground or DTC B1443 short to voltage.
-
This tests for an internal short to ground or voltage in the ignition switch. The key must be removed and installed as directed or a false diagnosis will occur.
Step | Action | Yes | No | ||||
|---|---|---|---|---|---|---|---|
Schematic Reference: Body Control System Schematics Connector End View Reference: Computer/Integrating Systems Connector End Views and Master Electrical Component List in Wiring Systems | |||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||
2 |
Does the scan tool display DTC B1441 as current? | Go to Step 5 | Go to Step 3 | ||||
3 | Does the scan tool display DTC B1442 as current? | Go to Step 10 | Go to Step 4 | ||||
4 | Does the scan tool display DTC B1443 as current? | Go to Step 10 | Go to Diagnostic Aids | ||||
Did you find and correct the condition? | Go to Step 14 | Go to Step 6 | |||||
Does the voltage measure +5 volts? | Go to Step 7 | Go to Step 13 | |||||
Can you measure continuity? | Go to Step 9 | Go to Step 8 | |||||
8 | Test the Off/Run/Crank and the +5-volt regulated power supply terminals of the ignition switch harness connector, for intermittent or poor connections. Did you find and repair the malfunction? | Go to Step 14 | Go to Step 12 | ||||
9 | Test the Off/Run/Crank and the +5-volt regulated power supply terminals of the BCM harness connector, for an intermittent or poor connections. Did you find and correct the condition? | Go to Step 14 | Go to Step 13 | ||||
Did you find and correct the condition? | Go to Step 14 | Go to Step 11 | |||||
Did you observe a short to ground or voltage? | Go to Step 12 | Go to Step 13 | |||||
12 | Replace the ignition switch. Refer to Ignition Lock Cylinder Case Replacement in Steering Wheel and Column. Did you complete the replacement? | Go to Step 14 | -- | ||||
13 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 14 | -- | ||||
14 |
Does the DTC reset? | Go to Step 1 | System OK | ||||
