• | 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. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
B+ | B1370 06, B1380 06, U0100-U0299, 2, 4 | B1370 06, B1380 06, U0100-U0299 | -- | -- |
Accessory Voltage | B1370 06, B1380 06, U0100-U0299, 2, 4 | B1380 06, 1 | B1380 01, P1629, 1 | -- |
Ignition 1 Voltage | B1370 06, B1380 06, U0100-U0299, 2, 4 | B1370 06, 1 | B1370 01, U0100-U0299, 1, 2 | -- |
Off/Run/Crank Voltage | B1370 06, B1380 06, U0100-U0299, 2, 4 | 1 | 1 | -- |
Run/Crank Ignition 1 Voltage | B1428, 3 | B1370 06 | -- | -- |
Accessory Wakeup Serial Data | U1814, 3 | U0100-U0299, P0513 00 | -- | -- |
|
The vehicle power mode master (PMM) is the body control module (BCM). The ignition switch is a low current switch with multiple discrete ignition switch signals to the PMM for determination of the power mode. The PMM receives the ignition switch signals, and additionally a reference voltage signal from the BCM, through the ignition switch, and back to the BCM. There are redundancies within the PMM system that can allow operation of certain subsystems when there are faults in the ignition switch circuits. Other information such as serial data input from other modules and DTCs is also used to determine what power mode signals and information is transmitted by the PMM. The BCM logic uses all this information to identify the operator's desired power mode and activate specific discrete signals, and serial data messages for the operation of different subsystems as necessary. Other modules which have switched voltage inputs may operate in a default mode if the PMM serial data message does not match what the individual module can detect from its own connections.
The PMM will activate relays and other direct outputs of the PMM as needed according to the calculated power mode. Some relays controlled by the BCM are switched ignition voltage outputs that are pass through circuits within the BCM directly from the ignition switch. If these circuits short to ground, the B+ circuit fuse to the ignition switch will open.
Ignition switch is in the OFF or ACC positions.
Ignition switch is in the START position.
Ignition switch is in the RUN position.
Ignition 1 voltage circuit is shorted to voltage.
• | Ignition 1 voltage circuit is open. |
• | Ignition 1 voltage, accessory voltage, or off/run/crank voltage circuit shorted to ground. |
• | B+ circuit of the ignition switch open or shorted to ground. |
• | Run crank relay coil control circuit open (including relay coil and ground). |
Accessory voltage circuit is shorted to voltage.
• | Accessory voltage circuit is open. |
• | Ignition 1 voltage, accessory voltage, or off/run/crank voltage circuit shorted to ground. |
• | B+ circuit of the ignition switch open or shorted to ground. |
BCM senses an open or short to voltage on the off/run/crank voltage circuit when both ignition accessory/run and ignition run/crank parameters are active.
BCM senses an open on the B+ circuit to the ignition switch while the engine is running. An open on the B+ circuit can be caused by a short to ground on any of the circuits listed below:
• | B+ |
• | Accessory voltage |
• | Run/crank ignition 1 voltage BCM terminal 19, X4 |
• | Off/run/crank voltage |
Off/run/crank voltage circuit is shorted to voltage.
Off/run/crank voltage circuit is open.
• | 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 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. |
• | 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. |
• | A short to ground in the run/crank ignition circuit of the run crank relay will cause an open fuse to the ignition switch. DTC B1428 should be current. |
• | A short to ground in the accessory wake-up serial data circuit will cause an open fuse to the ignition switch. DTC U1814 should be current. |
• | 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 will determine if there is a power mode fault. |
Power Mode Description and Operation
• | Circuit Testing |
• | Wiring Repairs |
Control Module References for scan tool information
⇒ | If either of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle. |
Ignition Switch Position | Current Power Mode | Ign. Off/Run/Crank (Terminal 5) | Ignition Accessory/Run (Terminal 3) | Ignition Run/Crank (Terminal 2) |
---|---|---|---|---|
Off Key Out | Off | Key Out/ACC | Inactive | Inactive |
Off Key IN | Off | Key In/Off | Inactive | Inactive |
Accessory | Accessory | Key Out/ACC | Active | Inactive |
Run | Run | Run | Active | Active |
Start | Crank Request | Crank | Inactive | Active |
Important: You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
⇒ | If the test lamp does not illuminate, test the circuits listed below for a short to ground. If all circuits test OK, replace the BCM. |
• | B+ terminal 4 |
• | Ignition terminal 3 |
• | Ignition terminal 5 |
• | Ignition terminal 2 |
• | Ignition voltage terminal BCM terminal 21, X4 |
⇒ | If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. |
Important: The ignition switch component test must be performed before proceeding with this test to verify the integrity of the switch.
⇒ | If the ignition switch does not test normal, replace the ignition switch. |
• | Ignition terminal 4 |
• | Ignition terminal 2 |
• | Ignition terminal 21 |
• | Ignition terminal 14 |
⇒ | If greater than specified, test the circuit for a short to voltage. |
• | Ignition terminal 4, X1 and ignition switch terminal 6 |
• | Ignition terminal 2, X1 and ignition switch terminal 5 |
• | Ignition terminal 21, X1 and ignition switch terminal 3 |
• | Ignition terminal 14, X1 and ignition switch terminal 2 |
⇒ | If greater than specified, test the circuit for open/high resistance |
⇒ | If not the specified value, replace the ignition switch. |
Ignition Switch Position | Terminals 2 and 4 | Terminals 3 and 4 | Terminals 4 and 5 | Terminals 4 and 6 | Terminals 5 and 6 |
---|---|---|---|---|---|
Off Key Out | Infinite | Infinite | Infinite | Infinite | Infinite |
Off Key IN | Infinite | Infinite | < 5.0 ohms | Infinite | Infinite |
Accessory | Infinite | < 5.0 ohms | Infinite | Infinite | Infinite |
Run | < 5.0 ohms | < 5.0 ohms | Infinite | Infinite | < 5.0 ohms |
Start | < 5.0 ohms | Infinite | Infinite | Infinite | 1275-1325 ohms |
Perform the Diagnostic Repair Verification after completing the repair.
• | Control Module References for BCM replacement, setup, and programming |