Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC B1372: Device Ignition 1 (ON and START) Circuit LowDTC B1373: Device Ignition 1 (ON and START) Circuit High
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
B+ - Terminal 2 | 1 | 2 | -- | -- |
Ignition - Terminal 1 | B1382, 3 | B1382 | B1383 | -- |
Ignition - Terminal 3 | B1372, 3 | B1372 | B1373 | -- |
Ignition - Terminal 4 | B1442, 3 | B1442, B2957 | B1443 | -- |
Ignition Voltage - BCM Terminal B7 X1 | 3 | 5 | B1373 | -- |
Accessory Wakeup Serial Data, BCM Terminal B6 X1 | 3 | 4 | B1383 | -- |
| ||||
Circuit/System Description
The body control module (BCM) monitors the ignition inputs Ignition Off/Run/Crank, Ignition 1 Run/Crank and the Ignition Accessory signals supplied from the ignition switch. The BCM uses the sequence that the signals appear, their voltage levels and the engine run flag (ERF) status to determine the power mode. Battery voltage is supplied to the ignition switch by a fuse in the underhood fuse block. The Run/Crank voltage circuit energizes the Run/Crank relay and is a pass through circuit in the BCM.
Conditions for Running the DTC
B+ is between 9-16 V.
Conditions for Setting the DTC
B1372
The BCM detects that the Run/Crank circuit is open or shorted to ground.
B1373
The BCM detects that the Run/Crank signal is shorted to voltage.
Action Taken when the DTC Sets
| • | The BCM stores DTC B1372 or B1373 in memory. |
| • | The BCM determines a fail-safe power mode dependent on the last valid power mode detected and the state of the ERF. |
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
The power modes and controls are determined using BCM logic. Comparing the Body Control Module Power Mode data display parameters listed in Circuit/System Verification to the scan tool values of the vehicle will determine if there is a power mode fault.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Power Mode Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
With a scan tool, observe the Ignition 1 Run/Crank parameter and compare the parameter to the Correct Ignition Switch Inputs table with the corresponding ignition key position. The Correct Ignition Switch Inputs table illustrates the correct state of these input parameters (circuits) in correspondence to the ignition switch position.
Ignition Switch Position | Ignition Accessory (Terminal 1) | Ignition 1 Run/Crank (Terminal 3) | Ignition Off/Run/Crank (Terminal 4) |
|---|---|---|---|
OFF | Inactive | Inactive | Active |
ACC | Active | Inactive | Inactive |
ON | Active | Active | Active |
START | Inactive | Active | Active |
Circuit/System Testing
- Inspect for an open B+ fuse to the ignition switch. The fuse should be OK.
- Disconnect the harness connector at the ignition switch.
- Verify that a test lamp illuminates between ground and the B+ circuit terminal 2 and ground.
- Perform the ignition switch component test. The test should pass.
- Ignition OFF, disconnect the X2 harness connector at the BCM. Connect the harness connector at the ignition switch.
- Ignition in ACCY, verify that a test lamp does not illuminate between ground and the run/crank voltage circuit terminal B8.
- Ignition OFF, disconnect the harness connector at the ignition switch. Test for less than 1.0 Ω on the run/crank circuit between BCM connector terminal B8 and ignition switch connector terminal 3.
- If all circuits test normal, replace the BCM.
| ⇒ | If the fuse is open, test the following circuits for a short to ground, if all circuits test OK, replace the BCM. |
| • | B+ to the ignition switch |
| • | Accessory voltage (ignition switch output) |
| • | Run/Crank voltage (ignition switch output) |
| • | Accessory voltage (BCM output) |
| • | Run/Crank voltage (BCM output) |
| ⇒ | If the test lamp does not illuminate, test the B+ 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.
| ⇒ | If the ignition switch fails, replace the ignition switch. |
| ⇒ | If the test lamp illuminates, test the voltage circuit for a short to voltage. |
| ⇒ | If greater than the specified range, test the circuit for open/high resistance. |
Component Testing
Ignition Switch
- Ignition OFF, disconnect the harness connector at the ignition switch.
- Using the Resistance Test table below, check the resistance between the terminals of the ignition switch listed in each switch position.
Ignition Switch Position | Terminals 1 and 2 | Terminals 2 and 3 | Terminals 2 and 4 | Terminals 2 and 5 | Terminals 4 and 5 |
|---|---|---|---|---|---|
Off Key Out | Infinite | Infinite | Infinite | Infinite | Infinite |
Off Key IN | Infinite | Infinite | < 5.0 Ω | Infinite | Infinite |
Accessory | < 5.0 Ω | Infinite | Infinite | Infinite | Infinite |
Run | < 5.0 Ω | < 5.0 Ω | Infinite | Infinite | < 5.0 Ω |
Start | Infinite | < 5.0 Ω | Infinite | Infinite | 250 Ω-10 kΩ |
| ⇒ | If any reading is not as specified, replace the ignition switch. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the repair.
| • | Control Module References for BCM replacement, setup, and programming |
